Brakes keep warping

[Adamrwake]

I have never used a forum before and I am wondering if anyone can help with the following problem. I have a B7 RS4 cabriolet. At present it has around 27,000 miles on the clock. I purchased this some 2 months ago and never noticed a wobble when braking on my test drive. But upon driving home and hitting motorway speeds I noticed a wobble of the steering wheel while braking but only between 75 down to 65 MPH. I purchased the car privately and had to fly up the country to pick up ( in hindsight maybe not the best plan) . When purchasing the vehicle the seller had full records of the car going into Audi garages for services/MOTs and repairs from the first day it was purchased, and the last shown was a service with new disk and brake pad change at Audi in Slough in January 2015 at around 23,000. I have a good friend who owns a mechanics Shop and racing team and took the car to him for an inspection. We changed the discs and pads for genuine Audi parts and I had no wobble while braking for 1400 miles. The wobble has now returned ( and is now very noticeable ) at 1700. But this now happens when braking between 45 down to 35 MPH. The garage I took the car to is very reputable and I also know they bedded in the brakes. I drove normally ( that is not hard, and 50% motorway miles 50% town) with no holding the brakes at stops etc. After looking deeper into the cars history it seems that this has been happening repeatedly for the last 15,000 miles ( no accidents that I can find or am aware of) and audi previously have changed the brakes and pads as good will. Has anyone ever come across this issue before? If so how was it resolved? I previously had a B7 RS4 saloon in 2009 to 2011 and never had this issue while putting 50,000 miles on the car. Any ideas welcome please. (Apologises for the long explanation )

[NJMAudiRS4]

Welcome and FON

Use the search function top right of the page, there is a multitude of info regarding brake issues and many about warping discs.

Is it an actual warped disc or could it be a build up of brake dust sitting inbetween the pad and disc, could be worth doing a couple of 3 figure runs then standing on the brakes down to about 20 mph then back upto normal driving road conditions/ speed then repeat a couple of times to see if it has cleared, then drive normally to let the brakes cool down.

Good luck with your search

[Adamrwake]

Thank you NJM

I have looked at the search section and now see a lot of previous questions and replies. I will have a look through there before I post in the future.

All the best

[Trups]

I had an issue recently, had a wobble, not an rs car but just as quick as an RS4, changed disc and pads all round and still an issue at certain speeds, seems the calliper at the rear was starting to seize and was getting stuck sometimes. New calliper bought and fitted and problem no longer present.

May be worth checking?

[mustdash]

I was going to suggest calipers too.

Your car has quite a low mileage on it which indicates it may have been sat for a while - in which case the caliper(s) may have seized on. If you've changed disks and pads and it's still happening then I'd be looking at calipers next.

[Adamrwake]

Thanks, I will ask the garage to check the callipers.

[toyneg]

I was going to suggest calipers too.

Your car has quite a low mileage on it which indicates it may have been sat for a while - in which case the caliper(s) may have seized on. If you've changed disks and pads and it's still happening then I'd be looking at calipers next.

+1

[Ellis]

Lengthy but useful post regarding RS4 brakes from several months ago in another thread...

I believe that the design of the brake disc is quite possibly the root cause of all the woes that RS4 owners have with brake judder. When I bought my car, I skimmed the discs front and rear to clean up the surfaces and fitted new pads at the same time. I had no problems with judder before or after skimming. I am always one for upgrading the brakes on any car I buy, and fitted AP discs and Brembo GT calipers after 2000 miles or so of ownership. The discs are mounted to custom made bells using bolts only, not bobbins. And this is where I think the problem lies with the OE disc.

On a racing car, the discs are mounted to the bells using a bobbin arrangement that allows for radial and linear disc movement: radial for expansion and contraction due to heat, and linear for reducing pad knock-off. Pad knock-off is caused by flexure in the hub and bearing assembly when cornering: the disc pushes against the pads and moves them away from the disc surface. When you next apply the brakes, the initial pedal travel is taken up moving the pads back to the disc surface again. Racing calipers further reduce this by having springs fitted behind the pistons. A fully floating disc assembly is quite noisy as the disc rattles when the brakes are applied. This is not the sort of thing you want for your road car, so the OE disc manufacturer fits anti-rattle spring clips to the bobbins. This effectively reduces or possibly even stops any true float that the discs may have as the spring clips are quite stiff. After a while road dirt and corrosion build up in the bobbins further reducing any float. And finally to the crux of this long winded waffle. When you have cornered hard and flexure has caused the disc to push against the pads, the disc moves in the bobbins but doesn't naturally return to a central position due to all the road dirt and corrosion. We know that the 8-piston caliper has really only one problem and that is also with corrosion. This corrosion occurs under the pad wear plates causing the pads to jam. With the poor design of the disc for the road and too tightly fitting pads, disc runout is the end result.

Of course, the cast iron disc can also warp, and uneven pad material deposit can cause harshness to the brakes, but the RS4 front disc is quite unique in its (poor) design.

[MikeFish]

As Nick said above, are you sure its not just pad residue on the disc? This is much more common than actual warped discs on the RS4.
A warped disc will be noticeable at all speeds and when braking from high speed it will feel like the car is shaking to bits. Pad residue will be only noticeable under medium braking. If you brake lightly or very heavy the brake will feel normal.

[davebirl]

any luck finding the cause of this issue?

[Covkiller]

Brake residue.
Mine were wobbling. I drilled my holes out and jet washed between the vents. Now there's no wobble and they're fine.

[FA57GTA]

Have you got powdercoated alloy wheels? If the wheel place get any/ bits of paint on the rear bolt and hub areas of the wheels, then it will affect the contact area on the floating brake disc. Take your wheels off and check, i had this exact issue and managed to get the alloy wheel refurb company to pay for new discs and pads on their insurance. Remember to scrape any excess paint off the wheel until the surface is flat before the new discs are fitted.