19 replies to this topic

[Peenee]

Had a great track day at Blyton yesterday, but my car suffered from some mild vibration when the brakes were hot and when braking very hard.

 

I'm running an AP Racing Big Brake kit on the front with floating discs on aluminium bells.

 

I've done quite a few track days at Blyton and never suffered this problem before. The brakes and pads have done around 10,000 miles (the car has only done 12,000 total !) and there is still a good 6 or 7mm of pad thickness left.

 

First lap out the brakes are fine.

 

Second lap starting to brake heavily and ok for a while and then I start to feel the vibration.

 

Third lap and the mild vibration is consistent - but doesn't effect the braking performance, the car will still stop on a sixpence!

 

Any additional laps and it doesn't get any worse.

 

Next session out on track and the same happens again.

 

Does anyone have any ideas what it might be?

 

P.S. Running standard calipers on the rear with floating aluminium bells and pagid pads and these all look ok - the car is fantastically balanced under hard braking.

 

Thanks.

 

 

[JohnTurbo]

Sounds like some play in your front suspension or steering. Ie:- Inner or outer steering joints, where inner is part of the rack. Loose wheelnuts! Vibration in wheel bearings. Otherwise possibilities:- Uneven pad deposits from overheated pads Warped rotors. Actually if your pads are the same all round you will be relying too much on the fronts imo, which does tend to hammer them.

[anz3001]

Sure sounds heat related, warped disc/rotor would usually be permanent. Might be the fixings that secure the rotor to bell?

[Arno]

Not claiming that it's the case here but often this is a sign of cementite development in the steel of the dics that shows itself mostly when the discs get up to their working temperature. It has markedly different friction and expansion characteristics from the normal iron so the pads start to run over 'bumps' == vibration.

 

This is often triggered by pad deposit on the dics during the initial bedding-in process. Often because the car was put away/stationary with discs that were still too hot and the area covered by the brake pads has reacted/cooled differently.

 

Usually only real option is new dics, new pads and proper bedding in and then a good cooldown of the brakes before 'real' use.

 

A way to test this is to (try to..) skim the brake disc on a lathe.. Let the machinist use an old tool bit because if it's indeed cementite development inside the disc then it will ruin his toolbit pretty quickly..

 

Bye, Arno.

[Zoobeef]

I got the nobles brake discs skimmed using an on the car lathe. They are definitely true to the hub then. Was about £50 a corner though.

[Peenee]

Thanks guys all really useful information - I understand all the theories and all could be feasible. But do you really think this could suddenly happen after 10,000 miles of mixed use on the road and on track?

 

I've done numerous track days, Cadwell and Blyton are local to me, but I've never felt this vibrating sensation before?

 

At Blyton, it happened within the first 2 laps of the very first session. I appreciate Blyton is a heavy braking circuit and I certainly didn't feel any vibration at Cadwell a few weeks earlier, but Cadwell is a much smoother track and the braking isn't as heavy?

 

Have the discs just come to the end of their life at 10,000 miles?

 

Thoughts appreciated?

[Peenee]

P.S. Where did 'Zoobeef' get your discs skimmed on the car?

[techieboy]

I had the discs on my Audi on-car skimmed. The kit they used was from a company called Pro-Cut and this is their list of companies that do it.

[techieboy]

Just noticed where you are. It was done by STS Wheel Alignment in Bedford.

[Peenee]

Thanks - Biggleswade is a bit of a lie - I work in Biggleswade, but I live near Retford in Nottinghamshire and this is where the car is!

 

I'll check STS in Bedford out though.

 

Thanks again.

[techieboy]

God, that's a miserable commute, with the Black Cat roundabout twice a day.

[Peenee]

Not too bad, I travel down on a Monday morning and then home on Thursday night, so the dreaded Black Cat is only twice a week!

[rasputin]

you may have just lost a weight off one of the front wheels

or if your running semis it could be rubber build up on tyre.

[Pidgeon]

Classic pad transfer symptoms.  Running Pagids by any chance?

 

You need to warm the pads up and down, too hard too early and this is what you get.  It will clean itself off over a week or two on the road.

[Peenee]

Running Pagids on the rear, but the pads on the front are the original standard AP pads.

 

We had the wheels off on the track day and there didn't appear to be any weights missing - also checked wheels were tightened.

 

Running fairly new; [font="calibri, sans-serif;"][font="calibri;"]YOKOHAMA A048 front and rear and they are very clean with no rubber pick-up.[/font][/font]

 

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[siztenboots]

had problem with A048 front tyres being badly balanced from new , got them replaced

[Peenee]

For anyone interested, I've found this and it makes useful reading; http://www.powerbrak...h_01_judder.htm

 

[kipper]

I had a similar problem with almost the set up that you have. 308 mm AP rotors on fixed ali bells. Tried most things including skimming of the rotors, and measuring the run out on the rotors on the car, and they were within AP specs. But still the problem with vibration through the steering column occured under moderate braking. However, after going over to BG floating rotors on the front the problem disappeared, now any vibration is caused by wheel imbalance. Using CL RC5's. 288mm AP ali bells and fixed rotors on the rear with standard calipers Regards Dave

[Peenee]

Finally got around to another track day at Blyton and my braking problem is cured.

 

Pad etching on the disc was the issue - you could see a 'shadow' impression of the pad on the disc, even after heavy braking!!!

 

Took the car to;

 

R. Nicholson Motors

1-7 Eastoft Rd,

Crowle,

Scunthorpe,

North Lincolnshire

DN17 4LP

 

01724 711410

 

They took the discs off, cleaned them, refitted and then skimmed them on the hups with their 'Pro-cutting' equipment and then fitted new Pagid pads - I'd normally do this bit myself, but as the calipers were off I thought they might as well fit them.

 

Brilliant job, no vibration under very heavy braking at Blyton and I daren't tell you how little they charged me, I would certainly recommend them for disc skimming.

 

[Kieran McC]

Drop Red5 a pm he had a similar problem with his in Zandzoot, His were not spaced out evenly the discs were catching the rear of the calipers.