Spax Shocks - Adjustment

[Steve Strain]

Can some one help with some ideas on how to arrive at a good setting for the front spax shocks?

Also
1. How many effective clicks are there (before the adjuster disengages itself inside the shock)? Is it 8 clicks, 12 or more?
2. How do you know if you have them adjusted right?
3. Is it safe to assume that say 5 clicks on one side would give the same result on the other side?

I am using the supplied coil springs which we decided on another thread were about 350lb inch.

Forgive my ignorance on this but my questions arise from a simple experiment.
With the shock adjustment backed off the car would pull left on hard sharp braking, possibly following the road camber (or due to some other issue).
However if I wind the screw adjuster up full on both sides (what ever full is since continual turning of the screw seems to do nothing hence question 1 above) and do the brake test again the car stops dead straight.

Any pearls of wisdom gratefully accepted.

Thanks

Steve
Steve

[chris.richard]

Wind them full soft, drive on a bumpy bit of road, and wind them up a couple of notches at atime until the front is settled over the bumps and not yo-yoing up and down. You want the minimum effective damping.
Can't see why they should contribute to a pull on the steering if symmetrically adjusted.
That's a rough laymen's approach, I suspect the resident professionals will have a more scientific method!

[chris.richard]

My old Spaxes are 14 click adjustment, according to the label on them.

[mudhut]

My Hawk can also pull rather unexpectedly to the left on sharp braking. Can't see how it can be the shocks themselves (also Spax) if they are set equally provided they are functioning correctly and your assumption number three is correct Steve.

I have the feeling that the steering geometry is changing unequally on each side during "dive" and what I'm experiencing may be a form of "bump steer" which might be attributable to steeering rack position. If greater damping is reducing the amount by which the suspension moves then this would at least be one consistent explanation for what I've experienced.

May have got completely the wrong end of the stick though...

[chris.richard]

My Hawk can also pull rather unexpectedly to the left on sharp braking.

Does that mean only sometimes? Doesn't sound desirable either way. Tyre pressures equal? Mine did the same last week - it was a soft front tyre.

[mudhut]

Wasn't a soft front tyre Chris - both at 18psi. Seems to happen when I least expect it! The sharper the braking the greater the effect. Perhaps I'm just getting more used to the feel of the car, but any way you look at it, something is either wrong or the set up of the car is exacerbating the problem.

Brakes are fine - first thing I looked at. Need to get out onto a large flat area to see if it is related to road camber but there aren't so many of them that don't draw unwelcome attention...

[rutthenut]

Perhaps I'm just getting more used to the feel of the car, but any way you look at it, something is either wrong or the set up of the car is exacerbating the problem.

Check the front tie-bars, and the mounting onto the chassis.
I think most kits have a rubber bush there, although a rose joint is used as an option on later cars.

If there is any amount of free play or excessive bush in the mounting, you will get unwanted steering effects under braking.

J.R.

[mudhut]

Thanks John - I'll look into that.

[Ken Tomblin]

Peter


It sounds very much like bump steer !!!!


Regards

[guy mayers]

I'd go with John on this one. Check the condition of the bushes on the front leading link. If they show any signs of wear then replace them, preferably with the uprated rose jointed/clevis pin variety. There was also a mod from the factory many years ago strengthening the from mounting point - just an axtra plate to weld in - as it was found that uprated brakes and bigger tyres were having an unwanted effect on this point - bending it!
Guy

[Martin K]

There was also a mod from the factory many years ago strengthening the from mounting point - just an axtra plate to weld in - as it was found that uprated brakes and bigger tyres were having an unwanted effect on this point - bending it!
Guy

Unfortunately with Metro 6R4 brakes, 220 bhp and sticky Dunlop slicks my chassis showed these problems in 1991.

It is a shock to me that Gerry finally did accept SOMETHING of the feedback I gave him from my rallying experience because despite my requests at the time, I was told that the chassis was perfectly strong enough - as good as the original chassis - and did not require any mods to meet the loads inflicted by competition.

[mudhut]

Thanks Guy. So my Safety Devices chassis is prior to the improvements Martin - yes?

Steve - I'm sorry: I appear to have hijacked this thread. I'll shut up now...

[chris.richard]

There was also a mod from the factory many years ago strengthening the from mounting point - just an axtra plate to weld in -

Anybody got any more details / pics of this? I suspect my 1993 chassis is, well, suspect! :)

[colin artus]

My recollection of the problem is this; The bracket that located the bush for the front tie bar on Spyder chassis' (SPY prefix) was made from folded 18g steel with an extra layer of sheet on the mounting face to take the pull/push load. This was adequate as long as the two plates were welded with no gap between them. It became apparent that on some chassis the two plates were slightly separated allowing them to flex (half the stiffness) leading to weld failure. A thicker bracket to weld over the top of the existing one was sent to anyone who had a problem in this area. Later Spyder chassis used a thicker gauge single sheet bracket which is how it should really have been done in the beginning - I wouldnt be suprised if it was simply because Spyder didnt normally carry any heavier sheet as the Lotus stuff was very lightweight.

[Steve Strain]

Hi Guys

It is nice to know someone else has the same problem. :o Thanks Mudhut.

When my car pulled to the left I tried a number of things to work out why.
I haven’t checked for bump steer recently but my last wheel alignment man said there was no noticeable bump steer.
My car has a clevis and rose joint to locate the front leading bar so I do not expect any movement here.
I have one of the last spyder chassis made. The front chassis mount is 7mm thick and appears to be two layers of welded metal.

Colin - Do you know if this is what I should expect? Is this the modification?

I am a novice at such things so rely alot on trial and error so here is what I did - with a drive test between.
1. Re-bled the front brakes
2. Swapped the brake pads from left to right (my 164 once failed a MOT braking test - they use rollers to measure the brakes on each axel - one side had a higher reading than the other. To fix this the tester suggested I try mixing the pads around on the front - this worked perfectly).
3. Wound both shocks back and advanced them the same each side (up to full-on)
4. Removed some play from the front roll bar mounting blocks by filing one surface and re-tightened them (this also cured an annoying rattle). I also checked there was no pre-tension on the roll bar.
5. I swapped the left disk rotor onto the right side.
You might be interested to know that although the rotors are new vented Wilwood’s I have been told by Wilwood them selves (after I complained they phoned me at home) to expect up to 8 or more thou “out of round and flat”. They say this is normal for their budget product.
The effect however is “knock-back” of the caliper pistons and pads meaning one side will activate before the other. I have measured the out of flat on left side at 2.5 thou.
Apparently only the high end Wilwood rotors are heat treated and reground flat. Also expect the mounting holes to be up to 22 thou from centre meaning you have to individually fit the rotors!
You can possibly tell this by rotating each wheel and listening for a scrape-scrape noise as the pads contact the high spots. I had the same problem when using the original Fiat 132 brakes. The disks were new but not flat this may have been made worse by occasionally overheating them.
6. I checked the corner weights
7. Moved more brake bias to the rear

I suspect the pull to the left was a combination of all the above and is really a setup/sorting issue.
At speed and in the wet I can still detect a slight twitch to the left if hard on the pedal but it then pulls up straight. There is no twitch if gradually press the brake pedal.
I think my next step is to have all 4 disks skimmed.