Vibrating when braking

[djt]

I had my brakes done allround about 6k miles ago but recently I have noticed when braking moderately to heavily I get vibration in the steering wheel.

Is this likely to be a defect with the discs or something else?

I currently have my RS up for sale, so this is something I need to get sorted out ASAP. Even if I do not sell (which is looking extremely likely) I want to get this sorted out as I like my car to be running perfectly.

The work & brakes are still covered under warranty but if it is something else, I will have to fit the bill. Just wanted a heads up before going to Audi as I cannot see them just admitting I need new brakes too easily when it will be them covering the cost.

[P_G]

When you say you had brakes done was the fronts or rears or both?

[adsgreen]

6k miles is alot for a warranty. Would ve surprised if they'd cover it.
As above - what work exCtly? New pads or both pads and discs?

Out of interest how is the car mainly used? Town driving or motorway?

Have you tried reversing the brakes in?

[djt]

6k miles is alot for a warranty. Would ve surprised if they'd cover it.
As above - what work exCtly? New pads or both pads and discs?

Out of interest how is the car mainly used? Town driving or motorway?

Have you tried reversing the brakes in?

All 4 discs and pads (I think), I will have to double check my paper work.

What's reversin them in.

Driving is a mixture of motorway, town and B roads.

[adsgreen]

Sorry - stupid iphone replaced "re-Bedding" with "reversing".

Assuming all new pads and discs then either they have been badly fitted (which to be fair you'd notice wa before 6k miles) or they have built up a layer on them from light braking causing uneven surface levels which manifest themselves as brake judder. It's usually town driving that kills brakes as you end up being very light on them as speeds are lower. Also it's all too easy to sit on the brakes at traffic lights.
With smaller less effective brakes ironically it's not so much of a problem as they heat up quicker and require a bit more force on the pedal to get similar braking results. With the RS4 the brakes are very large and for town driving a complete overkill. As such it's very easy to accidentially feather the brake pedal rather than press it. What happens is that only the microscopic high spots of the disc touch the pads and heat up. Now with modern brakes the braking force is a combination of fricting between the disc and pad (at low temps) combined with a transfer of pad material to the disc at high temps. When the high spots get hot the pad material starts to transfer... but only to the high spots and this creates a self repeating cycle as the high spots get higher making the problem worse.
Eventually the high spots are so high that you end up with an uneven disc surface creating the brake pedal/steering wheel wobble.

Unfortuntely it's quite possible that by the time you notice the effect there's not alot you can do other than replace of skim the discs as the build up can be hard to shift.
However for the costs involved it's worth giving re-beddin a chance as it can work and you've got nothing to lose.
Simply find a nice quiet fast straight road.
Perform so medium braking actions from about 60mph to 10mph without engaging ABS or stopping the car. The idea here is to get the brakes up to top end operating temperature so pad material is able to treansfer - so no need to go to mad. Just good firm braking. You'll need to do at least 7-10 of these and you should feel the car stop (and feel) much better as the brakes get up to temp.
Now you want to do about 3 really hard stops - racers would refer to it as "threshold braking". You want the absolutely maximum braking (again without ABS) that you can get pressing as hard as you can.cjc
After this go for a ten minute easy drive avoiding using the brakes if possible to allow them to cool. If you must come a stop then don't sit on the brakes and use the handbrake to hold the car.

This should make things better - you can repeat as often as required so if you start seeing an improvement then you may be in luck.

When driving normally try to avoid using the brakes lightly and don't hold the car on the footbrake when still.

[P_G]

Before you do that look and see if the drilled holes are clogged and if so clean them out. High spots are usually around these holes caused by clogging wsith brake dust.

[djt]

Thanks for that info guys, very useful and I will give it a go. As you say it is worth a shot and I am often guilty of sitting on the footbrake at the traffic lights. Funnily enough I never used to because of a thread I read on here once but I have gotten lazy. Hopefully I can get them back to normal again whilst having a bit of fun in the process.

I will update after I have had chance to have a go.

Thanks again

[adsgreen]

Let's us know how it goes.
In theory if you're pressing the brake pedal hard enough then the dust should be pushed through the holes.

[simonp]

mine was a worn track rod end!

[adsgreen]

mine was a worn track rod end!

That'd do it but you'd probably notice that under normal driving conditions without braking.
Also if you jack the car up and wiggle the wheel you would probably feel it too.

[P_G]

Let's us know how it goes.
In theory if you're pressing the brake pedal hard enough then the dust should be pushed through the holes.

Problem with that is if you pressure wash your wheels the water will often conjeal the brake dust in the holes and then the rest builds up. Using certain wheel cleaner will also bung the brake dust in the holes further. If I do pressure wash my wheel I also specifically blast the discs and then after drying take it for a quick spin applying brake to clean the discs up so there is no residual rusting on the surface.

[djt]

Let's us know how it goes.
In theory if you're pressing the brake pedal hard enough then the dust should be pushed through the holes.

Problem with that is if you pressure wash your wheels the water will often conjeal the brake dust in the holes and then the rest builds up. Using certain wheel cleaner will also bung the brake dust in the holes further. If I do pressure wash my wheel I also specifically blast the discs and then after drying take it for a quick spin applying brake to clean the discs up so there is no residual rusting on the surface.

I will also give that a go too.

I am pretty confident it is due to me using the foot break at traffic lights as it is a new 'bad habit' and it has only just started occurring. This also makes me hope the build up won't be too bad.

Just need to find a suitable road now to run up and down 7-10 times without being rear ended.

[Nobber]

I've got a bit of this going on at the moment too and it's quite unsettling. Tried the re-bedding last night and it's not made a lot of difference. I'm wondering if it is build up on the drilled holes.

Anyone got suggestions for break dust cleaner or any other chemical to de-gunk the holes?

[P_G]

Use a bradle or a metal rod. No cleaning spray really required, just a bit of elbow grease.

[Nobber]

Cheers PG. I'll give it a go at the weekend. I'm about to order new pads too, just researching which ones to get though.