Brakes

[mogul_x]

All,

I had a question or two regarding the brake setup on a Hawk - specifically, the master cylinder.

My car is a "standard" HF3000, with a bracket drilled to accept either the 3-bolt Fiat 131 1600 master cylinder and booster, or a dual master cylinder setup. I don't have either at the moment.

First question - any opinions on what would be the best setup for use with the Girling single piston calipers used on the Alfa 164? I know the Girling calipers aren't the best parts out there, but I'm on a budget, and I already have a set.

I may upgrade in the future, so if possible, a master cylinder that can cope with larger (i.e., 4-pot) calipers would be ideal. Bear in mind that the car is being built primarily for road use, but might see the occasional autotest or day at the track.

Second question - If Fiat 131 parts are OK, will parts off of a 2-litre 131 fit the same hole pattern as the 1600? 1600's were never imported here, and nobody carries spares for them.

Third question - If dual master cylinders are the better way to go, can anyone provide details regarding what parts are required, where to get them, or manufacturers' part numbers? The build manual mentions Girling .625 dual masters, but doesn't provide any details.

Lastly, any suggestions regarding the fluid reserviors would be similarly appreciated. Particularly with respect to the clutch master cylinder, which is a Fiat X1/9 unit mounted under the dash.

Thanks in advance,

[JohnB_SPY8808053]

For aftermarket pedals, I would look at Wilwood or Tilton. Both offer pedal assemblies & MC that should fit your needs. If you shop around, you should be able to get everything you need (pedals, 3 MC & remote adjuster) for around $400.

John B.


PS - Here are some links that might be useful:

http://www.wilwood.com/
http://www.tiltonracing.com/
http://www.pitstopusa.com/BRAKEPEDALS.htm
http://www.precisionbrakescompany.com/index.htm

[Jeff Davison]

Scott,

Finally decided to jump the Yahoo ship and swim over to the real UK site ;^P

Anyways, about using a dual mc Tilton....You will have to modify (cut, weld, fabricate) the front bulkhead to accept the mountings.

It was offered as an option from Hawk and that is how mine is set up.

I've attached a shot (hope it gets over hear) of the bulkead.

Jeff

[rutthenut]

My newer car has the Tilton pedal box assembly as offered by Gerry.

One thing I guess I should point out with regards this setup is that you have to be very careful with clearance between master cylinder reservoirs and the front panel - or use remote reservoirs that are mounted further back in that area.

I have used cylinders with short integral reservoirs and that will only just clear the lip on the front panel, just behind the louvres where there are inset into the fibreglass.

On my earlier car, I had a balance bar assembly welded in to the pivot bar that fits to the upright mounting panel, then fitted twin cylinders to that. This also needed short reservoirs for clearance, rather than the taller ones available.

For the hydraulic clutch, the kits uses the X1/9 master cylinder, so I also fitted the reservoir that comes from an X1/9 and put that in the under-bonnet area.

Back to brake systems, Guy Mayers has used a balance bar and twin master cylinders with a shared servo setup. This seems to be a pretty good way to get the extra pedal effort that may be needed or desired. It's also a neat installation in his car.

Me, I don't use a servo, but I do remember the massive pedal effort I used to need for maximum stopping power when the car had single-pot, sliding caliper brakes. Some form of maths can work out the ratios according to the brake pedal length and leverage, combined with the sizes of master cylinder(s) and piston areas, also affected by brake disc diameter and then the rolling diameter of the wheels. But that's far too much work and theory! Just comparing cylinder and piston sizes is enough, with the result being that smaller diameter master cylinders are what you want if you don't have a servo. With twin 0.625 master cylinders and a slightly increased brake pedal leverage from a modified brake linkage pivot bar, I am happy with the effort used to stop my car on the four-pot calipers it now uses (Wilwood rear, AP/Princess front).

[Stratos]

As my car is not a Hawk, I cannot help regarding what fits to the bulkhead, etc, but I can tell you that I converted my car to twin master cyclinders via a balance bar system that was designed to fit on a servo. It was very easy to modify to this from the single master cyclinder which was fitted to the car when I bought it.

I have attached a picture below.

I currently run Wilwood 4pots on the rear, and Hi-Spec Racing 4 pots on the front. I have 0.75 master cyclinder for the front, and 0.70 master cyclinder for the rear. I don't run a servo, and find the pedal pressure OK.

[Stratos]

Sorry, I forgot to attach the picture.

[rutthenut]

Originally posted by Stratos
I currently run Wilwood 4pots on the rear, and Hi-Spec Racing 4 pots on the front. I have 0.75 master cyclinder for the front, and 0.70 master cyclinder for the rear. I don't run a servo, and find the pedal pressure OK.

David,

I guess it would make sense for both of us to include some other figures here, as we've both left out the piston sizes ('cos I don't know those without tearing apart the brakes) and also the brake pedal leverage ratio ('cos I don't feel much like crawling around under the dash of my car).

The Tilton pedal box assemblies listed in the Demon Tweeks catalogue indicate that the pedal ratios are either 5.5:1 or 6.2:1 (may be listed for steel and ally pedals in that order, with the Hawk setup using the steel pedals).

Can I suggest that we try and measure the pedal arm lengths on our respective cars so that the ratio figures can be worked out? Need to know the length of the pedal arm from the pivot to the foot pad (centre of that, or bottom edge?) and also the length from the pivot to the point where the pushrod is connected. If there are any further levers that are not 1:1 ratio then they should also be included.

Of course, if anyone else out there wishes to take these measurements and post them, please do. I think it would make for a useful comparison point as there may be major differences between the kits.

[Stratos]

Originally posted by rutthenut


David,

I guess it would make sense for both of us to include some other figures here, as we've both left out the piston sizes ('cos I don't know those without tearing apart the brakes) and also the brake pedal leverage ratio ('cos I don't feel much like crawling around under the dash of my car).

The Tilton pedal box assemblies listed in the Demon Tweeks catalogue indicate that the pedal ratios are either 5.5:1 or 6.2:1 (may be listed for steel and ally pedals in that order, with the Hawk setup using the steel pedals).

Can I suggest that we try and measure the pedal arm lengths on our respective cars so that the ratio figures can be worked out? Need to know the length of the pedal arm from the pivot to the foot pad (centre of that, or bottom edge?) and also the length from the pivot to the point where the pushrod is connected. If there are any further levers that are not 1:1 ratio then they should also be included.

Of course, if anyone else out there wishes to take these measurements and post them, please do. I think it would make for a useful comparison point as there may be major differences between the kits.

John,

Will do some measuring tonight, and post full spec of my brakes.

[JohnB_SPY8808053]

Just a thought...

I am planning to use the Wilwood firewall mounted pedal assemblies as part of my Hawk LHD conversion. If you get the seperate Wilwood brake & clutch pedal units, they are available in a 7:1 ratio. I thought this would help some with the pedal effort and it might make it easier to route the steering column too. Wilwood also makes a very small MC designed for use with a remote resovoir.

John B.

[mogul_x]

All,

Thanks for the feedback. There's a lot of good ideas in there, but some are a little more involved than I wanted.

I was really looking for a list of equipment that would allow the retention of the stock pedal cluster and brackets. I don't want to get into the time or expense of fitting an entirely new pedal cluster.

Ideally, I'm interested in something that involves no welding or cutting, and as little drilling as possible. If that's just not in the cards, I'll have to re-consider some of the more extensive modifications.

thanks again

[rutthenut]

Originally posted by mogul_x
I was really looking for a list of equipment that would allow the retention of the stock pedal cluster and brackets. I don't want to get into the time or expense of fitting an entirely new pedal cluster.

Ideally, I'm interested in something that involves no welding or cutting, and as little drilling as possible.

OK, ignore all the comments about the Tilton pedal box stuff, that's more for information than a suggestion for you to change things (IMO).

With the standard Hawk pedal box assembly, the upright mounting panel in the front under-bonnet area is already designed to accept twin master cylinders (you may need to file the powder coating to get correct clearance when fitting these though).

You will however need to get a balance bar assembly and weld that into the pivot bar that is fitted to the mounting panel. Not sure where you should source that type of unit, but they are easily obtainable in the UK (Rally Design make them, Demon Tweeks list them, others do too).

The part you need to modify (or replace) is the simple bar that converts forward motion of the brake pedal push rod into rearward travel into the master cylinder(s). A standard setup just connects to the cylinder pushrod with a clevis, with a central bolt as the pivot point - actually as I think is listed in the build manual (!).

When you purchase the balance bar, it is little more than a steel tube with a smooth bore, within which is a spherical bearing that is mounted on a long threaded bar, generally using circlips and a shoulder mount of some sort. Threaded clevis mounts then screw onto each end of the bar and are adjusted up close to the ends of the tube. The clevis mounts then accept the pushrods from the master cylinders.

A tapped hole in the end of the threaded rod allows a remote cable adjuster to be fitted (these are always over-priced, IMHO) to allow changes to made from within the car. Rotating the threaded bar then moves the pressure point of the spherical bearing within the tube section, so changing the bias from one cylinder to the other.

If either brake circuit fails, the whole assembly should work in such a way that it 'locks up' and ensures effort goes into the remaining system. Careful alignment of the threaded clevises will affect how this works once the tube section reaches a certain angle as the faulty side allows the pushrod to dive through the cylinder with no pressure.

A somewhat vague description I know (no piccies right now) but the main point is that you can buy the adjustable balance bar components and just need to weld this into the correct position on the Hawk brake pivot bar so that it is aligned with the master cylinder pushrods. No need to do any welding or other modifications on the pedal box assembly too, which I'm sure you'll like to know!

[rutthenut]

My previous post assumes that you would want braking with adjustable front-rear bias, so need twin master cylinders.

Looking back at your original post, maybe all you want is a new master cylinder from a production car, with twin circuits (for safety, at least). I thought the manual indicated that 2-litre Fiat parts could be used as well as those from smaller engined donors, but that really is stretching my memory a bit!

[mogul_x]

John,

Your last two posts were much more in keeping with what I was looking for. Not that the other stuff isn't good info to have on the board for others, but it didn't address my immediate question.

As for whether I was looking for a dual circuit or dual cylinder setup - that's what I was trying to figure out!:D

I can go either way. All of my other cars are running vacuum boosted, dual circuit master cylinders. They've all performed well, but they are OEM systems designed to work together. Actually, let me take that back - my '73 Chevy Nova's braking performance is a little sub-par by modern standards. I'd have to say that one is performing as well as it was intended to by the manufacturer.;)

Since the Stratos replica is using master cylinders and calipers off of different cars, I wasn't sure if I could get adequate performance from the Fiat 131 master cylinder mentioned in the build manual. If it'll work as is, or with proportioning valves to adjust the balance of the 164 calipers, I'll use it. If the dual master cylender would make balancing the system easier, or provide improved braking perfromance, I'll use that instead.

Either way, I need a better description of what's needed than is given in the manual. Your message about the balance bar was very helpful. At least I know it can be done with only a few minor changes. If I can find some part numbers, I'll be in business.

Thanks,

[Stratos]

John, whose stupid idea was it to clamber around measuring pedal distances - my back is still hurting this morning!! Only kidding - but it was difficult to take really accurate measurements of the pedal.


OK, here's a specification of the brake system on my Allora.

Pedal to Pivot 310mm
Pushrod to Pivot 75mm

Therefore pedal ratio is 4.13

Now that surprises me as it seems very low. But even if I am completely inaccurate, and it was 315 and 65, that would only give me 4.85

I suppose that as this is a standard Lancia Beta pedal box, which was designed for use with a servo system, maybe it's about right - but it's quite a bit lower that you get with a Tilton Pedal Box.


Front Disc 305mm (4 stud 98PCD)
Front Caliper Type 4pot Hi-Spec Race Caliper
Front Caliper Piston Size 1.625inch
Front Master Cylinder Diameter 0.75inch


Rear Disc 284mm (4 stud 98PCD)
Rear Caliper Type 4pot Wilwood Superlite IIa
Rear Caliper Piston Size 1.75inch
Rear Master Cylinder Diameter 0.70inch


Hope that's enough info for everyone, but, if I left anything out, please ask.

[rutthenut]

Originally posted by Stratos
John, whose stupid idea was it to clamber around measuring pedal distances - my back is still hurting this morning!! Only kidding - but it was difficult to take really accurate measurements of the pedal.

OK, I've just checked the pedal lengths - thought I should do so after suggesting it!

On the Hawk pedal box assembly, the lengths come out at:

Pedal to Pivot = 8"
Pushrod to Pivot = 2"

That comes out at a ratio of 4:1, so less than you found, which does explain why the twin master cylinder was not so effective without a servo and when working with single-pot calipers.

Since the pedal pad itself is 3" in height, I measured to the centre of the pad, but you could work out ratios between 3.5:1 and 4.5:1 depending on where you press on the pedal...


Both front and rear master cylinders on my car are 0.625".

The disc and piston sizes will have to wait, I may find them written down somewhere!

The front vented disc is off a 16-valve Integrale (four-stud) if that helps at all. The rears are Wilwood units.

[Stratos]

Originally posted by rutthenut
The front vented disc is off a 16-valve Integrale (four-stud) if that helps at all.

That's the same as my back ones - 284mm

[GMC]

David, Why do you choose to have a large front master cylinder and a smaller to the rear, giving more pressure to the rear, yet both of your cylinders sound very big ?? , where John's looks more normal from my experience in rallying, or .7 to the rear or is it different with rear engine cars ?

[Stratos]

I have an adjustable balance bar on the brakes, so that I can adjust the amount of pressure to the front and rear.

With such large piston sizes in the calipers, using a 0.625 master cylinder was giving an excessively long pedal travel.

After talking to Geoff Beddoes at Hi-Spec, I took his suggestions for front and rear master cylinder sizes, and it seems to work just fine.

[Jeff Davison]

Here's a device I'm installing on my dual m/c brakes. It's called Sure-Stop. It's a brake fluid recirculator (which keeps the fluid a bit cooler - a VERY good thing!) and a front to rear pressure equalizer (this prevents rear lock up from the rears reacting first). It works very well in conjuction with the balance bar. This device is patented and is proven in a racing environment.
Cost is around $200 USD.

Here is the url of the "poop" page:

http://dpiracingproducts.com/surestop.htm



Jeff Davison

[rutthenut]

You will find that on the Stratos, the rear brakes seem to do a lot more of the work than those on the front. This can lead to some different requirements for brake limiting devices and so on.

Part of this is the mid-engined layout, which causes weight distribution (and grip) to be biased a lot to the rear. I think this comes out at about 30/70 front/rear to start with. That is just the static balance though, as the short wheelbase and high centre of gravity result in a large amount of weight transfer to the front under braking. I've no idea what the dynamic balance may be, but it certainly puts a lot more load into the front wheels under hard braking - which is accentuated if using slick tyres on smooth tarmac.

This weight transfer will be apparent on all cars, but is less obvious on a front-engined car, for instance, as the front brakes will do most of the braking in any case. Avoiding rear lockup is clearly a good move for stability and this shows up a lot with cars that have little loading on the rear wheels. Avoiding front lockup is more often a case of modulating the brake pressure a bit more sensibly.

I believe that John Whalley has fitted a brake pressure limiter into the front brake circuit because it is easy to lock up the fronts when first hitting the brakes whilst they are still lightly loaded. Moving more brake balance to the rear helps this condition, but then does not take advantage of the extra retardation available when the front does get more load during the braking process.

If you want to get into all of the technicalities, it is possible to set up suspension geometry to include an element of 'anti-dive', which takes effect under braking. This can cause the suspension (in theory, at least) to behave in a more harsh fashion, which can be to the detriment of braking effort if the wheels skip on an uneven surface. The anti-dive approach feeds in some of the weight transfer effort to the suspension links, which changes the attitude of the car (or keeps it the same). I do not know if this makes much difference at all to the weight loading on the front and rear wheels, although believe that it should have some effect.

To sum up, the Stratos seems to do most of its braking from the rear wheels, which can actually be fitted with larger brakes than the front as proof of this. Under circuit-type conditions, the fronts can be made to work harder, although this brings with it the need for the driver to brake progressively to take account of weight transfer before using the front brakes to the maximum.

This is one of the attributes of the Stratos, in that the driver is involved in the process of getting the car to go quickly, whereas some (most) other cars try to minimise the level of driver input and result in a boring driving experience - well, not always, but I think you know what I mean!

[rutthenut]

Originally posted by GMC
David, Why do you choose to have a large front master cylinder and a smaller to the rear, giving more pressure to the rear

The way I've worked it out, the smaller master cylinder diameter actually increases the amount of line pressure on that circuit, even though this initially seems to be ar$e-about-face (to me, at least). Then again, the main consideration is the distribution between front and rear and the ratio between master and slave cylinders (pistons) rather than the actual line pressure.

The theory of a braking system works through a number of leverage and pressure calculations, with brake pedal ratios being the first. I'll try and work through some of this theory just to raise any comments on my understanding of it.

As a side note, has anyone had a look at the Fred Puhn 'Brake Handbook', or whatever it is called? I don't know if that is up to date or relevant, but have read plenty of other books on theory and my favourite is still 'Race and Rally Car Source Book' by Alan Stanniforth (name may be spelt wrong there).

First figure to consider for the braking calculations should probably be the amount of pedal effort applied - or perhaps that should be the last figure? Let's assume that the driver will push on the pedal with a force of 25lbs, since that is easier for the maths (and that isn't my strong point - hence correction from 100lbs in original post)

With a pedal leverage of 4:1 (Hawk HF figures, easiest again) this translates to a force of 100lbs being exerted in the brake master cylinder(s). With a single cylinder, that figure can be used directly.

For twin cylinders, the force is split between the two cylinders according to any bias built in to the brake adjuster. Assume 50/50 for now, as if you want to work out the figures it would make sense to start at that level so that the full range of adjustment is available for brake bias to either side (end).

So, each cylinder will receive 50lbs force in this setup (or 100lbs if a single master setup is in use, adjust numbers from then on if you want).

This force is applied to the whole 'surface area' of the piston on the master cylinder, resulting in a figure of so many pounds pressure per square inch (no, I'm not working in metric).

If a cylinder has an area of one square inch, the pressure would then be 50lbs/sq.in. But if the cylinder were half the size (in area), the pressure would be double that, as the 50lbs force would be applied to half a square inch area, so giving 100lbs/sq.in. It's this point that leads to my comment on smaller cylinders generating higher pressures.

The flip side, as indicated by David, is that to move a certain amount of fluid through the system, the smaller bore cylinder will need to move twice as much, hence increased pedal travel. The flip side of this can be that the driver has a larger range of pedal effort available to modulate the brakes, but a long pedal could run out of travel or just be less confidence-inspiring (or easy to use) so is not necessarily a good thing.

To try and continue with the mathematical approach, the master cylinder bore area is calculated as PI*R^2. This means that a 0.625 diameter cylinder (radius 0.3125) has an area of 3.14 * 0.3125 * 0.3125 = 0.3 sq.in (approx) and a cylinder of 0.75 diameter has 3.14 * 0.375 * 0.375 = 0.44 sq.in (approx, again).

With the force of 50lbs on each of these cylinders, the pressure figures, calculated as weight divided by area, would come out at 167 lbs/sq.in and 114 lbs/sq.in respectively. That's the crux of the line pressure calculations as I see it.


At the wheel end, the calipers and their pistons will all receive this same amount of line pressure (I guess this is what hydraulics is all about). Hence a further set of area calculations is required based on the size, and number, of pistons in the calipers. I would expect that the pressure calculation is to be divided across all of the pistons/calipers in the circuit, so assuming that just the system has just one caliper per wheel, divide the pressure again for each caliper, giving either 83.5 or 57 lbs/sq.in with the maths used above.

For a single-piston caliper, the area is clearly derived from that of the piston diameter. For multi-piston calipers, the areas are simply added together. With the 1.625" four-pot calipers, that gives approx 10.2 sq.in piston area. For 1.75" four-pots, it is approx 11 sq.in area.

The force being applied to the brake pad is therefore calculated using the line pressure and the piston area. If the pressure were at 50lbs/sq.in and the area were to be 10sq.in then the force would be 50 * 10 = 500lbs (unless that should be divided). Not sure it even makes sense to convert this into a single force measure here, so that bit of my maths may be somewhat irrelevant. Needs a bit more thought to work this through, although the principles seem to make some sort of sense (to me).

In order that any comparisons may be simplified when considering different brake components, it is not necessary to work out the actual line pressure as all that is needed is the ratio between a master cylinder and the caliper pistons that it controls. The line pressure will vary according to the force put onto the pedal, with that also increased by the leverage from the pedal, which can also be changed for overall effect.

At the caliper end of things, the braking effort is then affected by the area of the brake pad (probably converting from pressure at the caliper pistons into a different pressure at the pad surface according to the differentials in their areas) and that leads to the co-efficient of friction between the pad material and the brake disc surface, which is in turn affected by operating temperatures.

With a co-efficient of friction, the amount of retardation exerted onto the hub can then be worked out by the diameter of the disc, hence the leverage over the central point. Then the rolling diameter (or radius) of the wheel and tyre is brought into play and that works as a ratio of the retardation effort at the hub.

This is more simple leverage really, as the outer edge of the tyre is at the extreme end of a lever that pivots at the hub centre, with the caliper being at a distance along that lever. This is how increasing disc diameter improved braking effort, disregarding any issues of brake cooling and the amount of latent heat that the disc can hold. This also has the reverse effect if larger diameter wheels and tyres are fitted, as the braking force is then reduced.

But one of the reasons for fitting larger wheels is to allow bigger brakes to be used, with improved leverage ratios coming out of the equation (as well as better heat management). Another consideration with larger brakes is the amount of swept area, but I'm not sure that affects the maths other than in the heat generated and distributed, but it is another area of benefit.

To continue the theme, the amount of braking effect on the motion of the car is then dictated by the co-efficient of friction of the tyres with the road surface (pretty obvious, really). Besides the tyre compound, tread pattern, construction, pressure and so on, and the road surface, this also concerns the size of the contact patch on the road and the amount of weight or loading on the tyre. This latter point is affected by dynamic behaviours as discussed before (weight transfer under braking, cornering or geometry changes).

This leads to the possibility of wider tyres having less grip due to the simple calculation of car weight on contact patch surface area. On dry surfaces, this is rarely going to be an issue in reducing braking effort, but it can be apparent in wet conditions. For instance, aquaplaning is brought about by poor water distribution on a large tyre but is also affected to some degree by the fact that actual surface pressure is lower when spread over a much wider tyre (Group 4 car owners will know all about this).

There are other issues that cause exceptionally wide tyres to mess up the handling too, when used on uneven surfaces, but this is a brake discussion so I won't go further onto that topic.


By the way, I'm quite happy to be proved/explained wrong on this topic, which is partly why I've described my way of thinking so that it could generate some feedback. This is the sort of thought processes that my mind can go through when considering the theoretical implications of design matters. It doesn't mean that I work it all out though, just that I do consider these different points at different times. :confused:

So, comment away!

[chris.richard]

John, how does this greater braking effort to the rear affect the use of 164 brakes on the Hawk? Does the feront discs / calipers go on the rear hubs, or do you need to change master cylinder as well? I'm planning on using Gerry's kit for doing this, but it sounds like it's not necessarily a straight 164 to Stratos transfer.

[Stratos]

I would agree with John's comments on this.

In the sort of tarmac stage rallying that I do, you find most competitors have front engined cars, so all the weight under braking is on the front wheels.

What little weight is on the back end is reduced still further by the weight transfer under braking, resulting in a very light-weight back end (for braking purposes).

The result of this is that most competitors go for HUGE front brakes, and then have small discs on the rear (some even retain drum brakes).

(Gerry (GMC) I'm sure you can probably confirm most of the above from your experiences with your TR7)

As John said, with the Stratos, you have an initial rear weight bias, but under heavy braking a lot of that weight gets transfered to the front.

In rallying (as opposed to the circuit racing which John does) you have to consider whether you will be driving on asphalt or gravel, because on gravel the weight tranfer will be reduced as the grip levels are much lower, so the weight transfer to the front under braking isn't as pronounced. Some of the venue where I compete are mainly asphalt, but have some bits of gravel around - AND you have the areas where people cut corners and pull dirt out onto the road (Apologies to those following me on the Sprint at Abingdon!)

I can also confirm what John says that the rear do a lot of the work.

When I used to rally Escorts and Minis (many, many years ago!!) I used to replace the front brake pads regularly, but rarely change the rear pads because they never seemed to wear out.

With the Stratos, I am replacing the rear pads as quickly as the front pads. So it seems both are doing about equal amounts of work.

[chris.richard]

Originally posted by rutthenut


With a pedal leverage of 4:1 (Hawk HF figures, easiest again) this translates to a force of 100lbs being exerted in the brake master cylinder(s).

If the driver presses with a force of 100lbs, and the pedal's mechanical advantage is 4:1, then the pressure on the master cylinder should be 400lbs, surely?

[chris.richard]

Originally posted by Stratos
I would agree with John's comments on this.

In the sort of tarmac stage rallying that I do, the rear do a lot of the work.

With the Stratos, I am replacing the rear pads as quickly as the front pads. So it seems both are doing about equal amounts of work.

What size of discs do you use, front and rear? Are both the same, or do you us vented/crossdrilled /grooved at one end?

[rutthenut]

Originally posted by chris.richard


If the driver presses with a force of 100lbs, and the pedal's mechanical advantage is 4:1, then the pressure on the master cylinder should be 400lbs, surely?

Oops, that's the first cock-up in that post. I did mean to include the pedal ratio into the figure and simply had brain fade on that point!:eek:

I'll edit the numbers just to put in a brake pedal force of 25lbs so that everything else should add up (barring other maths errors).

Apologies to those who get these posts out of order, but Chris spotted an elementary maths error in my earlier post. Thanks for that.

[rutthenut]

Originally posted by chris.richard
John, how does this greater braking effort to the rear affect the use of 164 brakes on the Hawk? Does the feront discs / calipers go on the rear hubs, or do you need to change master cylinder as well? I'm planning on using Gerry's kit for doing this, but it sounds like it's not necessarily a straight 164 to Stratos transfer.

I'm not familiar with the exact setup of this brake conversion, but the rear brake calipers will still go on the rear - for the handbrake.

Having a single master cylinder means that pedal efforts should be fine as the ratios between cylinders and pistons is basically as per a standard car.

As for the front-rear balance, I think that it will not be an issue for road use. There is a lot of scope for different brake setups on the car, from the HF2000 'standard' setup of Beta/132 brakes and onwards. I used to use Thema Turbo (or Croma Turbo) brakes and they worked fine for me and I only changed to bigger vented brakes to go circuit racing, where the extra cooling would be needed. Roger actually has my old brakes on his car now!

I cannot really say that the brake balance will be like using the 164 parts, but from what I have seen of them it is going to be quite a good and simple option (probably similar to the Thema/Croma brakes I used to have).

If anything else is needed, you may want to look at fitting a brake pressure limiting valve to the front circuit, as John Whalley has done. This would be easy to do and is also adjustable, so allowing you to tweak the setup according to what you find when driving it. I wouldn't go to the trouble of adding this part unless you do find that any improvement is needed though, it's probably going to just fine 'out of the box'.

[Stratos]

Whow, John, that's a big one!!

Actually, I think that is a very comprehensive review of most of the factors involved. Pretty complex isn't it.

One factor I feel none of us has mentioned yet is Spring Rates -especially on the front. A higher front spring rate, to a certain degree, will resist the rear to front weight transfer exhibited under braking.

I've got most of the same books as you John. After I'd read them all, I came to the conclusion that I would never be able to work out properly what I really needed, and that I'd just go for pretty much the same sizes all round.

I felt that using heavy late braking, I'd probably be able to run more braking effort on the front than the rear, but I couldn't prove it - so I had a look at several of the other mid-engined cars competing in the same rallies as me - mainly Metro 6R4, Darrians, and Jeremy Straker's GTM.

The Metro 6R4s seem to run the same size disk all round. The Darrians seem to use slightly bigger front discs compared to rear discs.

Obviously, just looking at the disc sizes on these cars doesn't mean that THEY have got the right combination, and obviously you can't see how their brake balance bar is set to see what proportion of effort goes to the front, and what to the back.

BUT, these are cars driven by experienced rally competitors, and are finishing in the top 5 or so on the rallies, so I guess it's as good an indication of what works as I would find anywhere.

I guess it comes down to the fact that what I currently have seems to work well for me, but might not work well for someone else because driving styles will also have an impact.

[Stratos]

Originally posted by chris.richard


What size of discs do you use, front and rear? Are both the same, or do you us vented/crossdrilled /grooved at one end?

Front 305 Ventilated and grooved
Rear 284 Ventilated, grooved, and cross-drilled

Don't read anything into the fact that the front aren't cross-drilled and the rear are cross-drilled - it was just a matter of availablility at the time of purchase. I think either grooved or cross-drilled would have been fine.

[Stratos]

Originally posted by rutthenut

164 brakes

it's probably going to be just fine 'out of the box'.

I think I agree with John here. Most of what we have been talking about is competition orientated, and if you are driving on public roads like we are driving in competition ................:rolleyes:

[chris.richard]

I'm intending to do some tarmac rallies when it's finished, I'm trying to work out where on the spectrum of "bog-standard road" to "WRC tarmac hooligan" I want /need/can afford to be. I'll never afford to be front line competitive, but good old british corinthian competing for the fun of it.

[rutthenut]

Originally posted by Stratos
Whow, John, that's a big one!!

Snigger, snigger :o

[Stratos]

Originally posted by chris.richard
I'm intending to do some tarmac rallies when it's finished, I'm trying to work out where on the spectrum of "bog-standard road" to "WRC tarmac hooligan" I want /need/can afford to be. I'll never afford to be front line competitive, but good old british corinthian competing for the fun of it.

Chris,

You sound about my position, I'm not good enough to be out for anything other than fun - actually, I'm not sure that's a complement :)


I decided that I wanted good brakes after watching a Darrian on an event a couple of years ago. I had noticed the size of his brakes in the service area, and thought they were well over the top. Then I saw him out on stage, and was amazed by how much time he was taking out of the other cars just under braking.


For reduced stage times, I reckon money spent on brakes is much better than money spent on making the engine quicker - and it makes the car safer.

[GMC]

I agree with you Dave, A local friend of mine as recently built a Darrian it has Metro front discs and Metro four pot calipers with .7 cylinder at the front and AP forest 4 pot and Escort disc at the rear with .75 cylinder. Only three weeks ago I seen this car in action and was more than impressed with the stopping power.

[rutthenut]

Originally posted by Stratos
For reduced stage times, I reckon money spent on brakes is much better than money spent on making the engine quicker - and it makes the car safer.

I agree with you on that comparison, but it can be even more effective to improve the suspension on the car. If you can corner quicker, you don't need to use the brakes so much and you are already quicker onto the next straight so need the extra acceleration that bit less (as if).

For reducing lap times, or stage times, paying for more power is generally the least cost-effective route. If choosing between brake upgrades and suspension upgrades, it will never be so clear cut. At least with brakes it is easy to get to a point where you can consider them 'good enough'. Suspension gets into more and more complexity and higher price, for less return. Engine costs can just go on and on forever!

[Stratos]

Yes, I agree John - Suspension and Brakes. They were the first upgrades I did to my car.

Suspension-wise I have Leda Adjustable Struts at the rear, and AVO adjustable shocjers at the front, plus appropriate spring rates that seem to suit my style.

I suppose you could go onwards to the Leda with remote reservoirs, or something like Proflex or Ohlins, but I would know where to start in specifying to them what sort bump and rebound rates I would require - anyway, shouldn't digress onto that in a thread about brakes.

[Jeff Davison]

Tried to post some pics here but had no luck. Tried a few times.

Anyways...here's the url to the Yahoo Group photo album where they're parked.

There are four shots of the front and rear brakes I'm putting together.

Here are some specs:

Front and rear rotor diameter = 11.8"
Front rotor thickness = 1.25"
Rear rotor thickness = .81"
Both rotors are vented and have gas vents.
Rotor material is ceramic coated titanium.
Front rotor weight is 3.7 lbs
rear rotor weight is 3.2 lbs.
Custom rotor hats (bells) 6061 aluminum
Caliper braket material 7075 aluminum using "nut-serts".
Calipers are "Outlaw" basically a Wilwood equivalent. The fronts have different piston bore sizes to compensate for pad taper.
Local laws require a mechanical parking brake, hence the wilwood mechanical spot caliper on the rears.
Mentioned before, I'll be using a Tilton pedal box with dual M/C's and the "Sure-Stop" recirculator.

oops...heres the url for the pics:

http://photos.groups.yahoo.com/group/stratosreplicaclub/lst?.dir=/Hi+Perf+Hawk+Brakes&.src=gr&.order=&.view=t&.done=http%3a//photos.groups.yahoo.com/group/stratosreplicaclub/lst%3f%26.dir=/%26.src=gr%26.view=t

If that doesn't cut it, just go to the photo section where the pics are in the folder titled "Hi perf Hawk brakes"

This is really just a ploy to get some activity going at the neglected of late Yahoo group ;^P

Jeff Davison

[Stratos]

Jeff,

You are only able to post one picture per message. Maybe you were trying to attach them all to the same message. The other thing is that pictures attached to messages are limited to a width of 500 pixels (This is an artificial limit which I set to help in the formatting of the displayed messages)

I will be adding a photo gallery to the site soon where registered users can upload as many pictures as they wish. Workload probably means about 4-5 weeks from now.



Anyway, your brakes in metric sizes, so that comparison with mine is possible.

Front and rear rotor diameter = 11.8" --- 300mm
Front rotor thickness = 1.25" --- 31.75mm
Rear rotor thickness = .81" --- 20.5mm

So this means you have gone for exactly the same braking effort front and rear, as regards discs, piston sizes, and pad sizes, but we don't yet know what your master cyclinder sizes will be.

I never put my rotor (disc) thickness, but I have exactly the same as you front and rear.

[Jeff Davison]

David,

going with 3/4" Dia. mc in front and 7/8" dia out back. I feel the fronts need a bit more pressure than the read and the smaller mc will do that. But with the fluid recirculator / pressure equalizer we'll see. It may be a while before the system is track tested.
Also will have the balancing bar knob mounted inside the car. To monitor the front to rear bias I'll be using an SPA dual digital readout guage. It shows alternately the front and rear proportion and the front and rear line pressures.

Please don't ask what I spent for the system ;^P

Jeff

[Jeff Davison]

Forgot to mention that I would have gone 1.25" thickness all around but the widest rotor that the mechanical spot would take is .81". I thought of an hydraulic lock for the parking brakes, but that would be illegal when I register the car for street use.

Jeff

[Stratos]

Originally posted by Jeff Davison
the fluid recirculator / pressure equalizer

the balancing bar knob mounted inside the car.

an SPA dual digital readout guage.



Jeff,

There's certainly some trick gear there! Impressive.

[Jeff Davison]

If anyone would like drawings of the parts I made, feel very welcom eto ask and I'll shoot them to you. I have them in .dfx or .dwg AutoCad format

Jeff

[rutthenut]

Originally posted by Jeff Davison
Forgot to mention that I would have gone 1.25" thickness all around but the widest rotor that the mechanical spot would take is .81

If this is the Wilwood parking brake that I've got on my car, then you could simply split the caliper and add extra spacers if you want to cover wider brake discs.

Maybe you've got a better brake, 'cos I'm not impressed with the one I've got (it needs a floating mount for it to work properly, so ends up with a 'flexible' mount instead, which is crap for adjustment purposes).

[Jeff Davison]

John,

It's the rattely Wilwood spot calper :(
Floating mount. All I could find for a mechanical stand alone caliper.

Jeff

[rutthenut]

Originally posted by Jeff Davison
It's the rattely Wilwood spot calper.
Floating mount.

Just had a look at your photos on the Yahoo site, looks like a really neat installation.

I can see the floating mount with the 'claws' that fit into the body of the spot caliper. Do you have any form of springs in the installation to get the caliper to sit over to one side until pulled across by the action of the wedge/piston? Not too sure how they could be added, but the idea seems to make sense to me.

[Jeff Davison]

No sprins other than the brake cable retraction springs.

The "claw" piece was a part directly supplied by
Wilwood and had no provision for centering springs.

Jeff

[Stratos]

Originally posted by GMC
I agree with you Dave, A local friend of mine as recently built a Darrian it has Metro front discs and Metro four pot calipers with .7 cylinder at the front and AP forest 4 pot and Escort disc at the rear with .75 cylinder. Only three weeks ago I seen this car in action and was more than impressed with the stopping power.

Was this the car that was competing on the Rally of the Lakes?

There was a brief glimpse of a Darrian on the RPM coverage shown on Sky Sports Rally Fever program.

[Stratos]

Originally posted by Jeff Davison
All I could find for a mechanical stand alone caliper.

Jeff

Why not just use any rear caliper from any car with a rear disk brake setup?

For example, why not just make a bracket and fit a 164 rear caliper, if your disk isn't too wide.

[Stratos]

Originally posted by rutthenut
The flip side, as indicated by David, is that to move a certain amount of fluid through the system, the smaller bore cylinder will need to move twice as much, hence increased pedal travel. The flip side of this can be that the driver has a larger range of pedal effort available to modulate the brakes, but a long pedal could run out of travel or just be less confidence-inspiring (or easy to use) so is not necessarily a good thing.


Just following up a little on this area of John's comprehensive post on brake theory.

I was replacing my brake pads last night ready for a rally at the weekend, and when the pistons were pushed back into the calipers, to make room for the new pads (therefore wider than the worn pads), there was a massive amount of brake fluid forced back out of the master cylinder.

When I saw how much came out, I started wondering whether even my very large piston sizes are large enough.

[Stratos]

Originally posted by GMC
I agree with you Dave, A local friend of mine as recently built a Darrian it has Metro front discs and Metro four pot calipers with .7 cylinder at the front and AP forest 4 pot and Escort disc at the rear with .75 cylinder. Only three weeks ago I seen this car in action and was more than impressed with the stopping power.

Another reason why you would be impressed by its stopping power is the low weight.

I was talking with Tom Lambert at our motor club last night. He has a Darrian powered by a 2.4litre Millington Diamond engine, which delivers almost 300bhp. The all-up weight of his Darrian in rally trim is 750Kg.

Power to weight ratio of about 400bhp per ton!

A lot less weight to slow down from speed, and less weight to be accelerated!

He's competing on the same rally as me at the weekend. Don't think I'll be anywhere near his times - I probably be a few HOURS behind!!!

[rutthenut]

Originally posted by Stratos
Why not just use any rear caliper from any car with a rear disk brake setup?

For example, why not just make a bracket and fit a 164 rear caliper, if your disk isn't too wide.

I think you've pointed out the problem there - the majority of cars on the road don't have vented rear discs, so there isn't such a large choice of standard handbrake calipers available.

When thinking on donor brake components, I got rather fed up trying to find out which cars have a handbrake mechanism on a vented disc, in conjunction with a four-pot caliper.

Those cars that do have four-pot rears (Porsche, Ferrari, et al) seem to have a separate handbrake mechanism, often working on as a simple drum brake assembly on the inside of the disc bell in some way. And then there is the cost of these parts to consider!

[Stratos]

Originally posted by rutthenut


I think you've pointed out the problem there - the majority of cars on the road don't have vented rear discs, so there isn't such a large choice of standard handbrake calipers available.

When thinking on donor brake components, I got rather fed up trying to find out which cars have a handbrake mechanism on a vented disc, in conjunction with a four-pot caliper.


Ford Granada Scorpio 4x4 Estate will provide a handbrake caliper which works on a vented disk.

[rutthenut]

Originally posted by Stratos
Ford Granada Scorpio 4x4 Estate will provide a handbrake caliper which works on a vented disk.

Cheers, I had heard of Granada braking parts being used but was nto aware of which model(s) may be suitable sources.

I guess this is not a four-pot caliper (or is it?), so not ideal for use as the only caliper in that type of system, but is obviously quite suited to use as an additional caliper for operation of the handbrake facility alone.

[David May]

I've got the Granada / Scorpio rear calipers on my Corse I and although they are only a 1 piston sliding caliper design, their pads are Escort Cosworth (loads of compounds) and the handbrake works very well.
As usual with all the weight on the back, the rears get a very hard life and mine eats pads, but they hold up well, even for hot laps at Monza.

Dave M

[Stratos]

Did some more research, and found that the following all had vented rear disks.

Porsche 924
Ford Granada (All,but Cosworth had larger discs)
Ford Scorpio (All,but Cosworth had larger discs)
Ford Escort Cosworth
Ford Mondeo 2.5 V6
Ford Sierra Cosworth
Toyota MR2 2.0 16v 91onwards
Honda Prelude 2.3 16v
Mazda RX7 85 onwards
Renault Alpine 3.0 GTA Turbo 91/92
Porsche 911
Porsche 944
Porsche 968

Quite a lot of Porsche 924 in breakers yards.

[Dave Watling]

The later Impreza Turbos (from 99 in the UK but earlier for the Japanese imports) also have vented rear disks either sliding or 2 pot calipers depending on the model.

[GMC]

I did the five stud converstion last week, and fitted the Alfa 164 front caliper and disc, but the front brakes are not as good as when I had the Fiat 132 brakes. ??
Yesterday I fitted .625 / .7 /.75 /.875 master cylinder and still feel the front brakes are not what I expected, To much effort and little stopping power, My pedal measures pivot to push rod 35mm and pivot to centre of pedal 235mm and no servo fitted.
Anyone out there have simuliar expierience ?? Or is there something wrong with my calipers ?
I feel I have no problem with the rear as I have kept the Lancia front braked on the rear and can lock them under braking using a .625 cylinder.
Another question If I decide to change from the Alfa front calipers but keep the discs, what other caliper (4 pot) would fit ? as there is very little distance between the disc and the inside of rim.

[chris.richard]

Could it be the pad compound is too hard, and needs to be very hot to work well?

[GMC]

No. I fitted genuine Alfa pads, but afer a few miles of trying to work them hard they work slightly better but nothing like what I had with the Fiat brakes,
I am thinking the problem is in the pedal, the measurement from the pivot point to the rod (35mm) is too short and I have too much pedal movement and little movement of the rod, but great leverage. but against that I have ideal pedal with the Fiat brakes last week !

[Stratos]

Originally posted by GMC

Another question If I decide to change from the Alfa front calipers but keep the discs, what other caliper (4 pot) would fit ? as there is very little distance between the disc and the inside of rim.

Gerry,

Hi Spec do a low profile 4 pot, which is what I fitted to the front of my car.

http://www.hispecbigbrakes.co.uk/

TEL: 01322 286850 (Speak to Geoff)

[rutthenut]

Originally posted by GMC
Yesterday I fitted .625 / .7 /.75 /.875 master cylinder and still feel the front brakes are not what I expected, To much effort and little stopping power ... I feel I have no problem with the rear as I have kept the Lancia front brakes on the rear and can lock them under braking using a .625 cylinder.

If this is an adjustable balance bar, does it still not resolve the problem with the bias wound towards the front?

Besides fitting the smaller master cylinder to the front brake circuit, you may want to use a slightly larger cylinder for the rear circuit, to change the static brake balance to begin with. Obviously a hassle element in needing to bleed yet more brake lines, but you may find that this gives more effort to the front brakes so that all of your pedal effort is used more effectively. Or maybe it might not!

If you still feel that more pedal effort is required, you could consider modifying the pivot link, rather than the pedal assembly. This would normally give a 1:1 ratio between top and bottom sections (where the top connects to the balance bar and the bottom is connected to the pedal linkage). Increase the length of the lower part slightly to give a bit more mechanical advantage and you may find that improves the braking all round.

I made a similar change to this part when I put four-pot calipers onto my car, some years ago, but wouldn't have thought it necessary for a single-pot caliper design. I recall that Guy Mayers fitted a servo unit when he installed four-pot calipers.

Whereas the standard (2-litre) kit used a single master cylinder with an optional servo, perhaps there is a need for different brake pedal leverage when using twin master cylinders and/or four-pot brake caliper systems.

If this is the case, Gerry would be able to make different recommendations according to the brake components being chosen - he could then perhaps offer different pivot links if required.

Or if the problem only arises when fitting a twin master cylinder setup with a balance bar, the recommendation may be to mount the balance bar assembly slightly closer to the pivot point on the supplied link, to change from a 1:1 ratio to something that increases the pedal effort a bit over the single-cylinder setup.

[mogul_x]

Guys,

Trying to clear up a little confusion regarding the link that goes between the brake padal and the pivot link on a Hawk.

The build manual says that a donor part is required from Lancia Beta. It's a rod with clevises on either end. Apparently, there are two varieties - one with female clevises on both ends, and one with a male clevis on one end, and a female clevis on the other. The manual says that the male type is not suitable.

I've been told that either is suitable, since you only need some parts off of it to attach to a link supplied with the car. My car didn't come with this link, so I'm not sure what is needed ,and what isn't. I know that Hawk cars can supply a link, but I don't know whether it is complete, or requires the aforementioned parts from a Beta.

Can anyone provide a little guidance here? I want to make sure that I get the right parts.

Thanks,

[rutthenut]

Originally posted by mogul_x
Trying to clear up a little confusion regarding the link that goes between the brake padal and the pivot link on a Hawk.

Let's see then - all assuming this is for the standard Hawk pedal mountings, and not a Tilton pedal box assembly.

The pivot link is basically a flat bar with a central boss going through it that allows it to be bolted into the master cylinder mounting bracket, which allows the bolt to serve as a pivot.

At either end of the pivot link is a hole (8mm?) to allow a pushrod to be attached using a clevis mounting. The top one would go to the master cylinder (or servo, if fitted). The lower one takes the brake pushrod, which connects to the operating lever on the brake pedal assembly. That lever also has a hole for a clevis mounting.

In all cases, a 'female' clevis fits to the link with either a bolt or a clevis pin going through it to secure the joint. This bolt/pin forms a further pivot point in the assembly.

The clevis mounts on the lower part are connected by the brake pushrod, which does not come with the kit (from what I recall). This is essentially something like a piece of 8mm studding, but I would recommend that you do not skimp on the strength of this part as you will depend on it for your braking effort! You should be able to easily obtain what you need, or have one made up by threading each end of a suitable piece of stock.

If the clevis at one end uses a left-hand thread, then obviously that allows for easier adjustment (but more problems getting the thread cut in the first place). As this is something you only tend to adjust during assembly, it's not such a major deal if it requires the clevis to be detached from the link or pedal lever to do so.

If you are fitting a balance bar assembly, the top part of the pivot link will be cut down and welded to the housing, through which runs the adjustable centre bearing. That's not something I guess you need to cover at this stage though.

[mogul_x]

Originally posted by rutthenut
The clevis mounts on the lower part are connected by the brake pushrod, which does not come with the kit (from what I recall). You should be able to easily obtain what you need, or have one made up by threading each end of a suitable piece of stock.

John,

The part I'm trying to get sorted is what you are calling the brake pushrod.

So, what you're saying is: I need two female clevis ends, (probably from a Beta :confused: ), with a straight rod in between, sourced from elsewhere.

I suppose that the brake pushrod could also be built entirely from scratch, or I could cannibalize a brake pushrod from a Beta, and modify to suit.

I measured the distance from the bottom hole of the pivot link to the operating lever on the brake pedal to be about 9.5" Does this sound about right, or should I make the brake pushrod a different length? Obviously, there will be some adjustment built in, but I wanted to see if that was a good nominal dimension. Any guesses as to what kind of adjustment range is required?

Thanks

[rutthenut]

Originally posted by mogul_x
So, what you're saying is: I need two female clevis ends, (probably from a Beta :confused: ), with a straight rod in between, sourced from elsewhere.

...

Does this sound about right, or should I make the brake pushrod a different length? Obviously, there will be some adjustment built in, but I wanted to see if that was a good nominal dimension. Any guesses as to what kind of adjustment range is required?

The 9.5" sounds about the right length (for a brake pushrod, stop smirking you lot) :eek:

Adjustment range would probably be less than an inch, with a real possibility of you needing to cut off the end of the rod if it is any longer than needed, as there is only so much room in the clevis for the threaded rod.

The adjustment is only for setup purposes, as once in place you are unlikely to change it. The final length would be dictated by the pivot link and the brake pedal when they are in their required positions. You would still have adjustment remaining in the system by altering the effective lengths of the master cylinder pushrod(s) if required.

I thought that these clevises were available from other sources anyway. Not sure if they were in the Demon Tweeks catalogue, or maybe from a brake suppliers' brochure (i.e. Tilton, AP). I would think it should be easy enough to find these in the USA without needing to pay for international freight.

Dunno about sourcing the brake pushrod itself, I can't remember what I did about that part.

[mogul_x]

All,

I'm still on the fence between single and dual master cylinders for my Hawk. I found a supplier in the 'States that has Girling master cylinders, so I thought I'd try to figure out what size I needed.

There are a lot of good suggestions regarding piston size in this thread, but I wanted to check the math for my particular application. Anybody have the formulas handy?

I'm looking at using the Girling single pot calipers and rotors from the 164. Piston size is 54mm (2.12") front, and 36mm (1.42") rear. Any other relevant measurements I need to do this right?

Also, does anybody know the piston sizes from the Fiat 132/ Beta setup used on standard Hawks? I'm also looking into whether a Fiat 131 master cylinder will work with the Alfa calipers.

Thanks,

[roger001]

Originally posted by mogul_x
All,

I'm also looking into whether a Fiat 131 master cylinder will work with the Alfa calipers.

Thanks,

I used the 131 master cylinder with a lancia thema set of calipers, the rear is the same as a 164, the fronts are slightly smaller pistons than the 164, this worked fine. I am looking to upgrade the fronts to 164 calipers and will run with the 131 master cylinder initialy.

The only addition was a brake proportioning valve in the front circuit (John Whalleys idea) to stop locking up the fronts in the wet, which works well.

[Steve_R]

Scott,

Check Stoptech's (http://www.stoptech.com/technical/) website ... lots of useful info and formulas for calculating brake torque, etc.

-Steve

[Stratos]

Guy,

This thread should be of interest to you.

[Chris J]

I think you've pointed out the problem there - the majority of cars on the road don't have vented rear discs, so there isn't such a large choice of standard handbrake calipers available.

When thinking on donor brake components, I got rather fed up trying to find out which cars have a handbrake mechanism on a vented disc, in conjunction with a four-pot caliper.

Those cars that do have four-pot rears (Porsche, Ferrari, et al) seem to have a separate handbrake mechanism, often working on as a simple drum brake assembly on the inside of the disc bell in some way. And then there is the cost of these parts to consider!

I've just thought of a car that has a mid engine and rear vented disc mechanical handbrake. (see pic)

[chris.richard]

And it's a................................?

[Chris J]

Have a guess.

There's a lot of them about.

[catswhiskers]

OK I'll start the ball rolling.

Toyota MR2...?

Mick

[Chris J]

Chris, Mick,

Think aluminium and glue!

There, that's narrowed it down.

[SUSIT]

Chris, Mick,

Think aluminium and glue!

There, that's narrowed it down.


Lotus Elise
:)

[rutthenut]

282mm diameter vented disc (same front and rear) - haven't found the width yet

Series 1 cars had some form of 'metal matrix composite' but later cars use Iron.
Go-faster models use cross-drilled discs.

But it's the caliper that is of more interest,
Web search seems to show that 111R has a single piston sliding Brembo caliper.

So, can be an option to use if putting vented discs on the rear and not going four-pot all round. Or maybe as a better alternative to the Wilwood spot caliper, if it fits over the rear discs being used (what width?). Bit of overkill perhaps, to have that plus a four-pot caliper. Probably costs more than the two-pot-plus-handbrake caliper reported on in other thread (from the 'monster big brakes' crowd, always forget their name)

[philfingers]

Citroen BX GTi 16v have the handbrake on the front axle I believe, obviously vented and quite large due to they're location and the configuration of the car. Maybe suitable for rear's on a Stratos

[guy mayers]

Sounds interesting! Looks like we need an expert or some pictures!
Guy

[strat6v]

The rep for rally design told me that wilwood are bringing out a handbrake caliper in the midilite size later in the year and also doing away with the ally piston/dust seals and fitting the stainless pistons. They already have a powerlite caliper, for 20-22mm x 280 mm discs with handbrake facility for sale. Size wise it compares to a dynalite but the piston sizes are smaller than the Hawk/bgc setup.
Hi spec have their handbrake caliper for sale too(after a long time!)

[roger001]

Citroen BX GTi 16v have the handbrake on the front axle

Correct - so do Citroen Xantias - however Citroen brakes are made to work with LHM hydraulic fluid - standard brake fluid would turn the seals to mush - not reccomended!!!

[Sando]

...also the Sierra Cosworth 4x4 and Granada Scorpio have 273x20mm vented rear discs and a 41mm piston handbrake caliper.

Needs a small amount grinding off of a protruding bit of casting to go over a 24mm/ 285 Integrale disc.
( I'll let you know if it works......next months job :))

Cheers
Bobster

[David May]

I thought the 252mm vented rear discs and Lucas/Ford calipers with integrated handbrake used on the Corse I were Scorpio Cosworth items. Makes me want bigger discs now!

[Sando]

ooops sory Dave I lied ..just checked ...Cossi 4x4 - 273mm rears.
..Still, bigger than 252! and the caliper is easy to mod to go bigger still if you wanted.
cheers
Rob