Slight rumbling when braking from high speed; discs?

[TonyHetherington]

Hi all

A quick mechanical question if I may please?

I have an Audi S4 (4.2 V8 / 4WD) and it has recently started developing a slight rumble when braking from high (xxx) speeds. Only when braking, so definitely a brake issue.

Pads were new 8000 miles ago and have plenty of life, but discs are low and will need doing next time pads are done.

Could the discs low-ness be causing the vibration? Wheels are fine as they were refurbed only a few months ago, so not out of balance (car is perfect when accelerating).

Thanks all
Tony

[monthefish]

Yes, certainly plausible. Any corrosion on the discs?

[TonyHetherington]

Do you mean on the surface of the disc (the braking surface) or on lips and things? On the braking surface it's fine but on the lips and the centre it's like all other discs - rusty but not bad.

[N88]

Yep sounds like discs to me.

ETA: Often the inside of the disc that gets particularly worn, worth having a look there if it seems fine on the outside.

Edited by N88 on Wednesday 25th August 15:55

[minimax]

I seem to get this intermittently on various cars..just bought a Scorpio Cosworth (stupid whim...) and the brakes were vibrating in this manner. One enthusiastic italian tune up later and no vibrations at all, even now (3 weeks later)

[TonyHetherington]

minimax said:

just bought a Scorpio Cosworth (stupid whim...)

Bloody fantastic car

[RDMcG]

any cracking on the discs?

[TonyHetherington]

Rightyo thanks all - new discs it is then!

I did try the "italian tune up" approach - I used to get rusty suurfaces on my Lotuses when I'd wash the car then roll it into the garage for 3 weeks and the pads would rust to the discs. A few massive stops and it was fine - though this isn't that problem.

[TonyHetherington]

RDMcG said:

any cracking on the discs?

Not that I can immediately see but will have careful look tonight

[Petrolhead_Rich]

My A4 has warped discs, as did my Volvo before that, they had new discs on (I brake hard!), with older (Thinner) discs its almost certainly the issue as they warp easier than a new disc.

[djon]

TonyHetherington said:

RDMcG said:

any cracking on the discs?

Not that I can immediately see but will have careful look tonight

Are they drilled? Look for small cracks 'crazing' out from them. Not an 'really' issue until they connect but not to be ignored.

[Davi]

Petrolhead_Rich said:

My A4 has warped discs, as did my Volvo before that, they had new discs on (I brake hard!), with older (Thinner) discs its almost certainly the issue as they warp easier than a new disc.

warp doesn't usually result in a low end rumble though, and you can usually feel a warp through the pedal.

have a look at the lip depth, could be that it is contacting the pad backing if severe enough!

[Petrolhead_Rich]

Davi said:

Petrolhead_Rich said:

My A4 has warped discs, as did my Volvo before that, they had new discs on (I brake hard!), with older (Thinner) discs its almost certainly the issue as they warp easier than a new disc.

warp doesn't usually result in a low end rumble though, and you can usually feel a warp through the pedal.

have a look at the lip depth, could be that it is contacting the pad backing if severe enough!

If its only when braking from high speed it will almost certainly be warping due to the increased heat IMO

Metal-Metal contact would affect it at all speeds...