boxsey911

I've had some minor brake judder in the past when using the car on track but nothing near as bad as I experienced yesterday on track. Not only was the pedal bouncing underneath my foot but the steering wheel was shaking violently. I'm aware of the school of thought that rotors rarely warp and that pads need to be bedded properly (I've read the stoptech article and follow that procedure). Some background:

1. There's no judder on the road.
2. On track there was initially no judder but it got worse the more and harder I used the brakes. Each time the outlap was OK but by the time I was on the pace it got really bad. Seemed as though the hotter the brakes got, the worse it was.
3. I changed all rotors less 1000 miles ago and the car has done 3 trackdays since (no judder on the first day, mild judder on the second one, really bad judder on this one).
4. Front pads are RS15 grey, rear pads are standard and are only about 25% worn.
5. I have 3mm spacer shims front and rear

There was a small benefit of the juddering problems.....in the final sessions I tried using the brakes less and consequently did faster lap times.

Although I've searched a lot of threads about judder, I'd appreciate any thoughts on the subject.

Rocket Rob

I'm not a braking expert but am wondering why you are running standard pads on the rear? Shouldn't you run some sort of track-oriented pad on both? I'm thinking that maybe your rear pads are over heating and causing the judder.

Unkle

Equally not an expert, but hey its never stopped me before

3mm spacer shims? Have you had the judder before these were fitted?

boxsey911

I think that's a very valid question Rob, so here's some background on that choice:

Prior to the rotor change I had Pagid RS15 front and rear. Great performance but the rear had a tendency to lock up under hard braking. So at the change I put standard pads in the rear to remove some of the bias (BTW I have the correct p/v for 4 pot rears). On the 1st trackday after doing this the brakes performed flawlessly. On the 2nd the judder appeared. So I inspected everything. The rear standard pads looked in very good shape (very low wear) and there were no visible deposits on the rotors. The front RS15 pads on the other hand were more than 50% worn and were crumbling at the edges. So I swapped these for new RS15s, flushed the fluid and re-bedded. On the way to the track they felt great but the juddering appeared as soon as I got on the track.

I too am wondering that even with low wear on the rear pads, whether they are doing very little work and the fronts are not coping with the high temperatures? Maybe I should try a day with new standard pads front and rear?

boxsey911

All input welcome

I've been using them to reduce some of the rub from the wider track tyres. They were on for the first trackday with no issues. I was wondering about them too but although I checked wheel nut torque through the day....I didn't do a simple test of taking the shims off to see if they made a difference.

Unkle

I was thinking its a possible weak part and could be distorting when running hot due to the material composite compared to the hub and alloy wheel, but its probably unlikely. However your post about the standard rear pads putting more load on the fronts sounds interesting, and more plausible.

Tuscany964

Unfortunately I think your rotors are warped. It does happen, happened to me this summer. Same thing happened, brakes worked fine until they get some heat into them then they judder like crazy.

Changed rotors smoothed out the pads - problem solved.

Nader Fotouhi

Are RS-15 Pagids? Do you have additional cooling to the rotors?

If RS-15 are Pagids, pad deposit, even if you think that you have properly bedded the pads, would be one guess, especially if you drive on the street. . My theory (and I have no scientific proof except experience) is that Pagids leave more deposit on the street because they never get up to temperature. Use some agressive stock pads during street driving to see if you can remove some of the pagid deposit and re-bed the Pagids at the track.

If you do not have additional cooling, it is possible that the rotors are warped as it does not take many miles for over-heated rotors to warp.

BTW, I have new Pagid Sport pads and OEM rotors on my wifes C2 and the car is shuddering on the street after only one track weekend. I am going to use some OEM pads and have her drive it before the next track day to see if it helps, as I do not suspect over-heating.

boxsey911

I think one of the problems with this type of judder is that I can't replicate it on the road. It's just not legal or safe to try and get the brakes up to the same temperature which makes it difficult to try a change to see if it works. i.e. on the drive home from the track you wouldn't think there was anything wrong with them.

I'm out on track again in a couple of weeks. At the moment, I'm thinking of changing the front rotors and putting standard pads front and rear to see how it goes (new RS15 front and rear is £400+). I'll keep hold of the front rotors I take off because if the judder isn't resolved I'll know that they're potentially OK.

Nb. I've seen other posts on hear about brake judder coming back quickly after changing rotors that they thought had warped but unfortunately there's been now follow up to say whether the problem got resolved.

The only other idea I had about the cause of the judder is that it could be a caliper bolt that loosens up when it gets hot (maybe I didn't tighten one enough?). However, I would think that would have caused judder on the first trackday with the new rotors.

bawmnot

Hi Steve, t'was a good day yesterday, eh?

I too have developed a brake judder, though in my case it has not gone away now brake system is cooled. Towards the end of one of the last runs the brake pedal became very soft/spongy. I let it cool for a bit longer than normal but had judder in the next run, which got worse as time went on. Drove it this morning and it is quite bad even when cold.

My favourite mechanic (you know who) reckons it is warped rotors, taking it in next week to check/fix - just in time for Curborough... I'm gonna have to rethink things though - this is the second time I've damaged the brakes in only 3 trackdays! I must be a harsh braker - might go to track pads for the next one to see if it helps.

Cheers Andrew.

Indycam

You can get your brakes totally cooking hot on the street by driving slowly with one foot on the gas and one on the brakes .

Tuscany964

I insist your front rotors are warped. And it does happen on the road you just need to be on a serious downhill section of a mountain road. That's how I warped mine. Or do what Indycam said...

boxsey911

Don't worry, I'm listening, rotors are already ordered as one of the steps to try...no mountains roads round here to test them though but might try Indy's method.

Indycam

How do they unwarp themselves . The problem goes away and comes back ? I have never had a disk unwarp itself .

I'm thinking that the rotors have build up problem .
Maybe if they were turned or ground and a rebedding ?

Tuscany964

It is exactly the same problem I had. They don't unwarp themselves, but the judder is only noticeable when the rotors heat up. Changing rotors solved my problem but maybe if they are relatively new "turned or ground" would do... and obviously you'd still have to smooth out the pads and rebed both.