Brake Vibration

[bruceb]

The brakes on my car have tended to vibrate slightly under normal and light braking. When the brakes are applied hard there is no vibration and they stop fine. I've lived with it for quite a while now but would really like to get to the root cause.

The front discs/pads are nearly new and the rears are in good condition with little wear. I've just measuere the disc run outs and all four discs run true with no more than 0.002" run out on the worst disc, which should be fine?

I've also noticed a slight vibration through the sterring wheel even when the brakes are not applied, The wheels have been balanced twice so far!

I'm at a bit of loss to know what to do next, any suggestions?

 

[bernard tester]

If the front wishbone bushes are worn this can cause brake vibration. Berny.

 

[Pickled Piper]

I would recommend going through a bedding in procedure. I've found over the years that this cures 90% of brake vibration / corrosion problems. The vibration you describe may be partly caused by uneven build up of pad material on the discs.

Try about five to ten maximum retardation stops from about 60mph. (make sure you have a clear road!). Brake as hard as you possibly can without inducing the ABS, when the car has slowed almost to a stop, accelerate back up to 60mph and repeat.

I've found that this cures the majority of the brake tremor/ vibration problems that I've come across.

pp

 

[Richard_Hamilton]

I've seen that method too: http://www.zeckhausen.com/bedding_in_brakes.htm

Not that I've tried it, but others swear by the process.

 

[clyde]

It could be that the brakes are binding on slightly due to corrosion behind the stainless steel plates in the callipers causing the discs to overheat. Mine did this a while back and although I didn't get any judder to speak of when braking, occasionally on long journeys I would get quite a violent judder through the steering. After a short rest the problem cured itself and it would then drive OK. I'm not sure if the discs warped temporarily then straightened again as they cooled or what but it was like the ABS was kicking in. Try feeling the discs to see how hot they are after a run with no fierce braking.

The OPC were no use at all in finding the problem.

 

[peterarcher]

Have you had your brakes stuck on after a recent wheel wash? The violent unsticking can literaly takes chunks out of your pads, that makes them judder until they smooth down.
Peter

 

[bruceb]

Ok a short update....I tried the pad bedding in process suggested by PP, theres defiantly no judder under hard braking.

There still appears to be slight vibration under light braking. however I'll know for sure after my drive to work tomorrow morning on more familiar roads,

 

[bruceb]

Its still there []

Next step is to take out the pads for a good clean up and more thorough inspection of the stainless backing plates as Clyde suggested.

Stupid question but how do you releaese the pad retaining spring type clips?

 

[clyde]

The spring clips are released with a big pair of pliers. Squeeze the middle bits together and when free the clips hinges at the top. Could be a bit of a problem to get the pads out unless the discs are newish and haven't yet got a ridge at the edge.
This link tells you all you need to know http://p-car.com/diy/brakepads/

 

[Sanjaytalwar]

My car does this - it's just had 4x new discs and pads. Wishbone bushes are the culprit - new RS A frames are waiting to go on as I type!

regards

Keith

 

[melsomp]

I test drove a 993 at a dealer which displayed the same symptoms, I suspected the brake discs but they looked o.k. upon visual inspection, also the tyres were quite worn. I bought the car after four new tyres and an alignment check, the vibration has gone away.

 

[bruceb]

Ever the optimist I though I'd pop down to the garage tonight and spend an hour removing the brake pads, cleaning it all up and reassembling with just bit of copperslip, sounded simple enough.

An hour later and I just cannot get the pads to move back far enough to pull them out of the caliper over the very slight ridge on the edge of the disc [] The pads seem mighty stiff in the caliper housing, which looks like it might be part of the problem

My normal technique (used on the SC with steel calipers) of using a screw driver blade to lever the pad and pistons back is just not the ticket with the painted 993 alloy calipers.

So is there some tip top technique of removing pads without chipping paint?

 

[Johnny C]

I have a similar problem, the brakes can judder when light braking is applied at speed on the motorway. First time it happened I thought I had a puncture and pulled over, as soon as I pulled away again the problem had disappeared. Now I get it intermittently.

It can't be recreated on normal roads, I need to be doing 60+ for it to happen.

Brakes and pads have had about 15K miles on them.

I did (until this morning) have a knackered steering rack. It's just been replaced yesterday and the wheels realigned this morning (9M have a new system). Robin said it could have been the steering rack. So I';ll wait and see if it recurs.

 

[Incept]

I have read the posts on this subject with interest, as I am currently experiencing the same problem.

My situation arose after the car had been stationary over the Christmas break and had not been driven for some weeks.

I had washed the car before storing it, but had attempted to dry the discs with some short starts and stops before putting it in the garage. When I took the car out for the first time, there was the characteristic clunk (quite severe in this case) as the breaks freed themselves.

On driving the car the vibration or wheel wobble was quite violent for a few miles. After about 30 minutes, it settled down a bit but was still not great.

I have experience of this issue from before my Porsche days with BMWs (but the sticking never created this wobble). Therefore, I thought I knew what to do: Follow the bedding-in steps as described.

This at first seemed to cure the problem until the discs heated up: It then became noticeable again. Clearly if the issue doesn't go away with further bedding-in, I'll have to take further steps as suggested.

However, this begs the question: How do we stop it happening in the first place?

It's not always possible to wash the car and then go for a longish run to dry the breaking components and in the winter at least, it might just defeat the object of washing the car in the first place!

I'm actually getting frightened to wash the thing (sorry: Him)!

Has anybody got any brilliant answers: Blowing off the moisture with compressed air, or putting a heater in the garage for example? I'd really be grateful for an answer, as the car doesn't get run all the time as I work from home.

Regards,

Chris Waite

 

[Pickled Piper]

Always, always, always take it for a drive to dry the discs after washing. It is by far the easiest and most effective way.

pp

 

[Incept]

Which is fine unless you live in farming land like me. You're likely to undo the last 2 hours work unless it's the ideal, nice, warm summer's day. There must be another way.

Cheers,

Chris

 

[John Maddox]

If you are careful you can clean the car without wetting the discs too much. Clean the wheels by hand with a damp cloth rather than jet washing.

Obviously once in a while you need to clean properly. I use this stragegy without problem.

 

[bruceb]

ORIGINAL: MoC2S

Bruce, you may have jumped the gun slightly .. do you have the anti-squeal fitments installed (normal case). If so these will prevent the pads pulling out. Either remove the caliper complete with pads or do some deft work with an appropriate scraper - the anti-squeal things just stick on the back of the pad.

The pads are difficult to back off anyway, there are special tools which will assist, but caliper removal is often the easiest method ...

Have you read the p-car.com diy stuff, and pertinent tech articles ?

HTH, cheers, Maurice []

Maurice..great link, I'll try again at the weekend, this time a bit more informed, thanks[]