Brakes again

[chris.richard]

Finally got fed up with not getting my brakes to work properly, and got ringer in to show me how it's done. 3 hours of bleeding and swearing, and he came to the conclusion the master cylinder must be FUBAR.
Decision time - dual cylinders/balance bar or replace the status quo? I've trawled through the archive, and still not entirely sure what the best mastercylinder setup is for the Alfa 164 calipers. Seems to need modification of the pedal ratio if you go the twin route. More expensive too - about £150 for the bits I reckon.

Since a new 131 M/C is £16 + VAT, I'll stick that on while I think about it.

[chris.richard]

Right, well, bugger.
Fitted new brake Fiat 131 M/C. No difference to lack of brake performance. I see that the Fiat M/C is 19mm, while the Alfa one is 22.2mm. I wonder if I'm just not getting enough fluid displacement with the smaller cylinder.
Has anyone achieved adequate function with this setup?

Since I'm using new discs/calipers/pads/mastercylinder with Goodridge hoses and no leaks with standard Hawk mechanicals, I can't see where else I'm going wrong.

And I'm beginning to get really pissed off. :mad:

All help and advice gratefully considered.

[strat6v]

I didn't want the hassle from the standard setup so i binned it in favour of a underdash pedal box. The pedals are much longer and have a ratio of around 6.25 to 1. Its a job to convert but probably worth it. Would you like some pics? If so forward your email again and i'll send them.

John

[Bernard]

Chris
See pm
Cheers
Bernard

[chris.richard]

19mm M/C (Fiat) = 283mm squared area

22.2 (Alfa)= 387

twin 0.625" = 383

So decreasing pedal travel for same volume displacement. Maybe the 19mm M/C just doesn't let me move the caliper pistons far enough. :confused: Oooh I'm going round in circles and I'll disappear up my own.......AAAAAAAGGGHHH!!!!!!!!! :eek: :(

[rutthenut]

Is that maths correct for the final entry?

Using Pi = 3.14, diameters quoted for different cylinders, and formula area = pi x r^2

19mm diameter = 9.5 radius, piston area = 3.14 * 9.5 * 9.5 = 283mm2
22.2mm diameter = 11.1 radius, piston area = 3.14 * 11.1 * 11.1 = 387mm2
0.625" = 15.875mm diameter, per cylinder radius = 7.9, single piston area = 3.14 * 7.9 * 7.9 = 196mm2, double cylinders = total piston area of 196 * 2 = 392mm2

As you indicate, the larger master cylinder area results in less pedal travel for same fluid displacement.

But more important is the line pressure generated, which is what can result in a 'hard' pedal - and that in turn gets converted into piston travel and pad/disc friction pressures when the brakes are used. That in turn can be affected by the diameter of the brake disc and wheel, but we are getting away from your initial problems now.

If you are having trouble when bleeding the system, I wonder if there is a problem with the travel in the master cylinder, where the port is either not closing soon enough, or is not opening quite as it should? If the cylinder, piston or pushrod are not in the correct position, maybe that would cause a problem?

Even so, I didn't think any others had this level of trouble, especially using generally standard parts on the braking system.

Any further thoughts or progress?

[Stratos]

Didn't Bob Sharp report similar problems in a newsletter article?

[chris.richard]

Thanks John.
I can't see the mastercylinder being a problem - both the original and a brand new one give the same result.
With the engine off, I can get a semi firm pedal with a long travel, but can still turn the wheels by hand with the brakes on! With the vacuum on the pedal is soft as **** .

If I go for a larger M/C area, I'd reduce the pedal travel, firm up the pedal and cause more travel in the calipers. Which might all solve the problem, particularly if I do it without a servo. But given the similarity in area between the Alfa 22.2mm M/C and the twin 0.625 setup and the fact the 164 has servo assistance, it might not work with no servo.

Dave - I've read Bob's bit in the old newsletter, but still don't know what the solution was!

[strat6v]

One suggestion is, If you still have the 164 servo and m/cyl could you not use that, and modify the hawk linkage to give the same ratio?

[chris.richard]

I don't have one, but it could come to that!

[guy mayers]

Spent today trying to bleed the brakes......................... Three reservoirs, two empty and one full. New brake lines as I've ditched the ABS since going five stud, wiring is still there so I may have another go sometime. Out with the trust Gunson pressure bleeder and attach it to the reservoir, tyre at 15psi, (amazingly all 8 bleed nipples were not seized!) but it won't blow the fluid through. Tried a combination of pumping, valves open, pressure on and off and higher but all I get from the rear circuit is a dribble. Took the pipes off the master cylinders to check for blockages but still nothing (fortunately as I was expecting a BF shower!) when it finally dawns on me........ two empty reservoirs and one full one. Pipes replaced so the full one I'm trying to bleed must be the sodding clutch............. Ok, so trace the plumbing rather than rely on memory and find the rear reservoir, connect the air to it and there's this horrible hissing - one of the unions has a faulty flare on it. Fortunately I hadn't filled the reservoir at that point! Once cured the system worked just as it's supposed to and 5 minutes late the fronts are bled as well.
Now all I need is for the overhauled handbrake callipers to work when I try them tomorrow and that's a big job out of the way. Must be going senile. Either that or it was the heat in the garage today stopping my brain working! Yeah, I reckon it's senility as well!
Oh, and I guess I'll need to road test it sometime to make sure the brakes actually work! But that's a while away yet.
Guy

[chris.richard]

:D
Glad it's not just me!!

[rutthenut]

Ok, so trace the plumbing rather than rely on memory

Something I spotted on Dave's car was some simple lettering on the bulkhead area above/behind the master cylinder reservoirs: F, R, C

I guess that referred to Front, Rear amd Clutch. Seemed a really good, and simple, idea to me.

In case memory fails you again in future, you might want to write something similar on the front of the cylinder reservoirs?

[guy mayers]

Got a simpler one now! One of my other passions is aircraft so the predecessor of the Royal Air Force was the Royal Flying Corps - RFC, easy and I won't forget it!

[shaun]

Just put some fluid in my system, std fiat mc, 132 fronts, beta rears. Used a whole tin (485ml) of fluid to obtain a poor pedal so it's not just your set up. The next tin can wait until next month by which time the engin e should be in and i'll need some brakes then! Can't face 3L worth of fluid, but of course I did not bench bleed the mc, the caliper pistons were probaly not at the best point and the hand brake was initially left on - it's only everyone else who has the problems, NOT.

[chris.richard]

Spoke to Gerry - why didn't I think of that before? The Alfa calipers work with twin 0.625" M/Cs. The Fiat M/C doesn't. I knew the second bit!

[chris.richard]

I've got the twin M/Cs and balance bar installed, and all the new piping to go with it. My pressure bleeder doesn't fit the reservoirs, so it's been gravity bleeding apart from the right front where I can reach the caliper with a foot on the pedal at the same time! Gives a reasonable pedal, perhaps a bit more travel than I would like, but it seems to work, and won't get softer when the engine starts. Now I've to blank off the vacuum tap on the intake and re-install the centre tunnel etc. that had to come back out to get at the brake pipes.
I broke the clutch reservoir in the process somewhere :mad: , so I'm waiting for a replacement to arrive.
Soon I'll be back to where I was a month ago... :rolleyes: