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Brake Shudder - High Speed

scam75

scam75

Well-known member
Evening Guys

I've had this phenomenon since I got the car just over a year ago. When I brake from high speed the whole car shudders a bit, not necessarily through the pedal, more like the whole car. From 60 downwards it disappears.

When I got it it had a pretty bad shudder through the car when braking, like a warped disc. I stuck new rear discs on it about a year ago and the problem lessened but still stayed. I then changed the front discs and calipers and that made no difference.

I have changed the steering shaft and the tie rods and that seemed to lessen the problem again but not eradicate it. There is ever so slight play in the rack but don't think that is the culprit.

Has anyone else experienced this? Could I have a new disc that has slightly warped or would that cause shudder all the time when braking?

Confused!

Stuart
 
Stuart,

If it's a warped disk then it will show with a Dial Test Indicator. Find (buy - they're only £20 or so - borrow or beg) one and test it. Spec is less than 0.05mm run-out (from memory - check it) and it's easily tested.

However I had a similar problem with the fronts on my S2. As it turned out, I wasn't using a torque wrench to do up the wheel nuts, and this was the critical bit in getting rid of my shudder. Are you torquing the wheel nuts up correctly?


Oli.
 
I had that, and of all things, the runout on one of the rear hubs turned to be out of true. It felt like the brake shudder came from the front, which had me sanding disks, changing pads, retorqueing things, but no siree. Rear hub & bearing.
 
... and that's a good point that Sean makes; vibration (like noise) can travel most deceivingly around a car, making it very hard to know where it is coming from. Investigate carefully otherwise you'll risk simply changing all the parts that could be responsible, until you hit lucky.

You say you have changed the disks. One particular brand of disk (Zimmerman, as sold commonly by ECP and GSF, I think) had a very bad reputation on here for warping at the drop of a hat; whether the reputation was deserved or not I don't know but several people had problems with them, and I avoided them when I swapped the front disks on my S2. Do you know what brand you used on yours when you replaced them?


Oli.
 
Very, very rare for brake discs to warp with normal road use. Even with moderately hard track use too.

Far more likely that the discs haven't been mounted completely true. This is where Oli's dial gauge comes in handy. To check for warping, surely you're just better off taking the discs off and laying them on a flat surface to see if there's any variation in shape?

What kind of shape are your bushes in?
 
Where are you based Stuart? If you want to borrow my DTI (Dial Test Indicator) you'd be most welcome to.

I'm in East London, but can post it if need be.


Oli.
 
Hi Guys

Cheers for the replies! I have been torqueing the wheels so that rules that out. I think the discs are pagid all round. The rear discs were done by an indy, the fronts by me and Alasdair. Fairly sure the fronts are good, will check the back ones again.

I think Alasdair has a DTI gauge. Will pm you if he doesn't.

Stuart
 
Make sure the face of the hub and back of the wheel are nicely clean. A tiny bit of grit will cause the mating surfaces to be 'out of true' and can cause vibrations
 
Ok, I have a bush which has pushed out of it's proper location. Bottom half of the drop link at the rear ARB, drivers side.

It's mostly slid out of the drop link towards the gearbox. Could this be the culprit?

Stuart
 
OK, drop links ordered and will also check rear disc mating surfaces at the weekend.

Stuart
 
Got the car up on Alasdair's ramp today. There is a bit of run out on the rear O/S disc. This was not helped by the mating surfaces not being cleaned up by a local indy when the rear discs were done.

Alasdair cleaned up the surfaces and the problem has diminished but not disappeared. Another check showed still some run out on the disc so the disc will need swapped over.

Hopefully it's the disc and not the hub. Will try another disc next week at some point.

Stuart
 
Check the calipers are working correctly, a couple of the pistons on my front calipers were sticking when i first got it due to standing they must have seized, the brake judder was horrendous, whipped the pads out operated the brake pedal so the pistons came out against the disc cleaned them up and lubricated them and worked them in and then back out a couple of times, now sorted.
This after i changed front ARB bushes and was about to change a suspension arm.
Should take an hour or so to check.
Jim.
 
could it be a bush wobbleing?

i've got a capri and because one of the tca bushes is knackered it vibrates and pulls to the left under hard brakeing.
 
I solved my clutch problem a long time ago by replacing it! I think you are mixing me up with Mr Spaghetti who was due to see Alasdair this weekend!

Alasdair has become a good friend since I got the '44 so I'm a frequent visitor!

Cheers

Stuart
 
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