Brake judder over 40mph - worse when hot ..... ideas????

[Ireland]

I have been having trouble with a brake judder at the front of the car for a while now.

It's only noticeable above 40mph and it seems to be worse once the car has warmed up.

It can be felt back through the steering and sometimes causes the steering wheel to vibrate quiet badly.

I'm thinking a slightly warped brake disc that distorts even more once it gets hot ..... but that's just my thinking.

What do the rest of you think and, if it is a case of new brake discs, where can they be sourced from?

[GreenV8S]

Have a read of this, might explain your problem:

http://www.stoptech.com/tech_info/wp_warped_braked...

[Ireland]

Bedtime reading .....

[cerbielee]

Does sound like the discs! can you feel the pedal vibrate also? if you can then its deffo the disc's! if not then it can be a number of things! bushes, ball joints,dampers ect! One sure way to stop the discs warping is to drive a bit slower! or dont brake for bends

[Ireland]

I'll take it out for a spin and see if there's a judder back through the pedal.

I've been so pissed off with the vibration through the steering when I brake that I haven't taken notice of the pedal.

Perhaps the fact that I don't know if there's a vibration in the pedal means there's probably not one.

But I'll check .....

[Ireland]

Right, I got out for a spin this evening and there is a slight judder back through the pedal.

Most of the juddering can be felt through the steering wheel but there is a very definite judder under-foot.

[jonbarrett]

I'd put money on a warped disk. It' exactly what happened to mine. OK cold, hot brakes start to judder, new disks, all fine. It also happened quickly. One day everything was fine the next it started juddering.

[Ireland]

Is there and easy way to confirm that a disc is at fault?

By the time I get home, get the car jacked up, take the wheels off and start looking at the discs they have cooled down to the point where, when I rotate them they look fine.

[cerbielee]

They will look fine! even when hot,the warping is only usually a few thou of an inch! but that is magnified through the pedal and steering! if you can feel it through the pedal its deffo the disc's you can take them to be skimmed on a lathe but on a car like a cerb i wouldnt!

[jonbarrett]

I think my local garage removes the wheel, clamps a dial gauge to a fixed point, puts the probe on the disc and spins the disc. Minute distortion will be seen. Magnetic dial gauges on ebay starting £10. Disc skimming is not recommended, definitely not for drilled discs.

[Steve_T]

jonbarrett said:

I think my local garage removes the wheel, clamps a dial gauge to a fixed point, puts the probe on the disc and spins the disc. Minute distortion will be seen. Magnetic dial gauges on ebay starting £10. Disc skimming is not recommended, definitely not for drilled discs.

The only thing that cured my brake judder was new discs. I went for 330x28mm grooved APs (retaining the original bell) and they're absolutely fantastic.

[Ireland]

Who sells the AP, or other alternative, discs?

[cerbielee]

Have a look here!
http://www.racetechdirect.co.uk/product-subsection...

[Steve_T]

Ireland said:

Who sells the AP, or other alternative, discs?

I got mine through BG Developments and spoke to Roddy.

Steve.

[Ireland]

I got a mate of mine to call over last night and confirm my suspicions about the brake discs.

In the past he's prepared hot-rods for the track so he has a fair idea how things should be.

Using his old test method we worked out what's happening.

The front ones are definitely warped ever so slightly.

There is about 1mm of distortion across the RHS one and close to 2mm distortion across the LHS one.

I'm going to bring the discs to the local engineering works that does all our work stuff for us in the next couple of days and have him spin them on the lathe to confirm how much out they are at speed.

[Steve_T]

1mm and 2mm !!! Time to get some new discs I'd say. Discs have a minimum thickness as a service limit (whether you can find this out for TVR discs I've no idea) and if you true them up on a lathe I'd be concerned you'll take away too much metal.

Steve.

[Ireland]

The idea is to spin them on the lathe to see how bad they really are.

I doubt skimming will be an option.

Unless they turn out to be only slightly out of true, then it'll be a new set of discs.

I'll have a look in the service manual tonight to see if it's got any info on wear tolerances ..... but I doubt it will have.

[SlvrCrb]

Ireland said:

The idea is to spin them on the lathe to see how bad they really are.

I doubt skimming will be an option.

Unless they turn out to be only slightly out of true, then it'll be a new set of discs.

I'll have a look in the service manual tonight to see if it's got any info on wear tolerances ..... but I doubt it will have.

JJ, literally the day before the Alpine tour, I started to get judder just as you describe and my only option as I didn't have time to wait for discs to be delivered was to nip to a mate's local workshop and skim them quick. I dial guaged them and there was about 3 thou difference across the disc and so I had then skimmed and all was fine for about 300 miles and then it was worse then ever. God knows what a couple of mm feels like!!! The only real answer if the "brake from a ton and scrub" method fails is new discs. Vented for preference

[Ireland]

SlvrCrb said:

..... God knows what a couple of mm feels like!!! .....

It actually can sometimes feel like the whole front of the car is about to fall off.

The strange thing is that it can sometimes feel worse to simply touch the brakes lightly than to press them really hard.

Does this make sense ????

[Ireland]

I took the discs off tonight.

I'm heading over to the engineering shop in the morning and the man there is going to spin them on the lathe to see how bad they really are.

He said today he might try skimming them but I'm not sure if I want to put them back on the car skimmed.

I expect that a new set of front discs will be on my shopping list by tomorrow lunchtime.