Brake Judder on 993

[polar993]

I wonder if anyone can help me with a problem that re-surfaced last night. When I bought the car three months ago (993C2 50k miles 96N), the garage said they had replaced the rear discs, but a few weeks later (after having gently bed them in), I heard a rumbling coming from the rear of the car and a slight judder coming through the brake pedal, which was more pronounced at high speeds and when they were warm. Sure enough, skimming the discs solved the problem, but only for approx 800 miles, and last night it started doing it again. Ok, I was driving fairly quick, but I know it was nothing that would really test those brakes. Slowing to a gentle stop with consistent pressure on the pedal reveals a noticeable warp, but I just cannot understand why they are warping so seemingly easy. Could the garage (not OPC) have put on non-manufacturer approved parts? Could there be another problem with the car making them overheat and subsequently warp? Any suggestions would be gratefully received, as I am finding this bloody frustrating.

[james s]

Check the calipers are not sticking - they can do by this age. My 964 has this problemm and I ignored it, only to crack a rear disk at a track day a few months later due to overheating.

Still not sure how a bit of sticking did so much damage but it did. JZ machtech do a refurb service. A word of caution; the pads have rather more room than they need following a refub and tend to clunk about a bit which is a bit mildly irritating

James

[AC79xxx]

polar993 said:

Could the garage (not OPC) have put on non-manufacturer approved parts?

An easy way to check this is to look at the bell of the disk - the bit the alloy bolts onto. If it's painted with what looks like grey primer, then it's most probably an OE disk. If it's bare metal (or going rusty like mine are ) take the disks off, go back to your supplying dealer and bury them in the back of his head for fitting copy brake components

[henry-F]

As sugested ensure the brake caliper plates haven`t lifted. This happens when corrosion forms on the brake caliper body under the stainless plate that the brake pads slide on forcing the plates to bow outwards trapping the brake pad.

When the plates lift they don`t allow the pad to back off the disc when you remove your foot from the brake pedal thus causing an excess build up of heat.

It`s not a hard or big job to cure, most garages want around an hour and a half a corner to correct. Obviously as with all things brake related do a complete axle (ie don`t do the left hand rear but leave the right hand rear).

It is possible that there is a flaw in the brake disc it`s self. It`s not unheard of.

Henry

[polar993]

Thankyou gentlemen - the car is going to the garage tomorrow with your suggestions relayed, and I'll check the bell of the disc this evening.

cheers,
Adam

[nick_968]

Some good info on brake problems here.


www.stoptech.com/whitepapers/warped_rotors_myth.htm

[manek]

I've got a similar problem which, said one gareage, could have been caused by washing the car then putting it to bed in the garage. Slight corrosion of the still-damp pads/discs causes pad material to transfer to the metal, hence the slight vibration. Sounded plausible to me but what do I know?

So now I take the car for a blast after washing and before bedding it down in clean new straw (I made that last bit up).

[polar993]

My mechanic mate (he has a 964 so knows his stuff) has looked at the car and the callipers are moving freely with no major corrosion on the steel plate therein. However, the bell of the rear discs is rusted, as opposed to the fronts which are painted grey. Also, the fronts have the part number inscribed, whereas the rears do not. Not OE parts then, seemingly the obvious culprit. Have a call in to the garage I bought it from and will be requesting new OE discs for the rear. I'll let you know how I get on

[Andiroo]

Ran 993 and 996TT 380mm front and 320mm rear caliper and rotor setup (ala Brembo, Porsche and Sportec) for trackdays on my RS4 and came across several problems with non Brembo and non Porsche products. The excess weight of the RS4 (1700kg) also accelerated the problems you guys seem to have.

Any rotor that was OEM Porsche/Brembo or Movit etc and was skimmed would only last another 500miles if you were lucky (front or rear). With it being a cast item skimming is proven to be a complete waste of time coz you are actually building more warp into it in terms of rotor balance weight. If anyone recommends skimming then they are stupid and don't understand physics and brakes.

OEM Porsche and Brembo rotors for these calipers (just 4 pot fronts) are in a different league to any other replacement. As long as you keep them clean, especially between the rotors, and deglaze them (and the pads) say every 3k miles you will get at least 22k miles of wear including loads of trackdays. If u use the Sport Yellow Split pads then reduce the deglazing task to every 1k miles (ballache I know, but well worth it).

Hope this helps.

Andiroo





>> Edited by Andiroo on Wednesday 9th June 11:42

[roygarth]

Andiroo said:

Any rotor that was OEM Porsche/Brembo or Movit etc and was skimmed would only last another 500miles if you were lucky (front or rear). With it being a cast item skimming is proven to be a complete waste of time coz you are actually building more warp into it in terms of rotor balance weight. If anyone recommends skimming then they are stupid and don't understand physics and brakes. Andiroo >> Edited by Andiroo on Wednesday 9th June 11:42

Are you sure? I ask as mine has just been skimmed all round when new pads were fitted, by a specialist with a good reputation in the P world.

I've never heard of anyone saying you should not do it.

Piers
993RS

[polar993]

By way of an update, the garage has agreed to replace discs, pads and pad mounts next week. Hope that solves it

[Andiroo]

roygarth said:

Are you sure? I ask as mine has just been skimmed all round when new pads were fitted, by a specialist with a good reputation in the P world. I've never heard of anyone saying you should not do it. Piers 993RS

Unfortunately even some Audi tuning guys offer this service - although a lot don't

Firstly, all I can refer you to is the physics of the process, which when you think about it totally defies logic. I mean how can skimming correct a warped cast item apart from making it a lot thinner(subject to even worse warping) or worse redistributing weight?

Secondly, ask any S4/RS4 owner with uprated rotors and calipers how long a skimmed disc has lasted.

Thirdly, I know how many discs I have been through, both OEM/Brembo/Sportec and even Movit, supposed warped and supposed skimmed - maybe its the 1700kgs that makes it different from you guys?

Good news re the warranty btw.

Andiroo

[silver993tt]

The discs on my 993tt were skimmed about 2000 miles ago due to rust on the inner faces. They're great now and I've had no problems even using them on the German autobahns from speed of 140-150mph.

[Andiroo]

Hey Silver, not sure if the same 'Skimming' process is used for de-rusting a rotor surface as it is for a warped rotor?

The ones used on mine in the past are like a vertical lathe that holds and rotates the rotor and skims on both sides within whatever tolerances are preset. They are also sometimes used (believe it or not) to de-lip a rotor. If they cannot align both sides within a certain time or distance the rotor is destroyed. Does that sound familiar?

Andiroo

[roygarth]

manek said:

I've got a similar problem which, said one gareage, could have been caused by washing the car then putting it to bed in the garage. Slight corrosion of the still-damp pads/discs causes pad material to transfer to the metal, hence the slight vibration. Sounded plausible to me but what do I know? So now I take the car for a blast after washing and before bedding it down in clean new straw (I made that last bit up).

Yep, I always go for a spirited drive after car washing.