Newish brakes warped?

[B19GRR]

Hi all,

I had new discs and pads fitted all round at the end of September at the local garage. Got about 3k on them now and I'm getting really bad judder up through the steering wheel as I brake. The frequency slows as the car slows so I'm fairly certain that it's brake related. There is the outside possibility that it's BMWs famous shimmy caused by control arm bushes but I had the suspension checked over and a 4 wheel alignment shortly before doing the brakes and got a clean bill of health on them. I was thinking of jacking the car up in the morning and giving the wheels a spin. I'm guessing if the discs are warped then the wheels won't spin freely, is that reasonable?

If the discs are warped any ideas on where do I stand regarding having them replaced given age/mileage on them?

Cheers,
Rob

[Rockatansky]

I am of the opinion that brake discs don't warp, what you are describing is uneven brake pad deposits or pad pick up.

Good reading here: http://www.stoptech.com/tech_info/wp_warped_braked...

You *might* be able to clean them up, it might even be worth trying to re-bed them properly.

FWIW I had this recently on a set of rear discs with less than 1k miles and had to replace them.

[B19GRR]

Yep I've considered this and it's definitely a possibility. As to whether discs can warp or not I dunno, never experienced anything like this before. I did follow that recommended bedding procedure immediately on collecting the car especially as it's an auto so brakes get used more due to lower engine braking. Other than that I'm always pretty light on the brakes modulating my speed with the loud pedal wherever possible. Not had a chance to spin the wheels yet though. Also I guess I should get the wheel balance checked, they should be OK as they were just refurbed and balanced up by the refurb company but for a few quid it's worth checking.

Cheers,
Rob

[Mr2Mike]

Rockatansky said:

I am of the opinion that brake discs don't warp,

They absolutely can warp, though it's likely not the most common cause of juddering brakes.

Edited by Mr2Mike on Tuesday 10th November 19:37

[GreenV8S]

I think unequal pad impregnation is a more likely cause, especially on an auto where you're likely to come to a full stop with the brakes on. (This causes uneven impregnation especially during the bedding-in process.) It's possible to measure the discs for flatness if you want to make sure, but in your case I'd start by taking a close look at each disc and see whether the surface looks uneven. If the pads have impregnated it unevenly leading to hot spots and hard patches it's often visible to the naked eye in the right light.

[Rockatansky]

Mr2Mike said:

Rockatansky said:

I am of the opinion that brake discs don't warp,

They absolutely can warp, though it's likely not the most common cause of juddering brakes.

Fair comment.

I have only ever bent a disc (a motorcycle one, through physical impact) but never warped one.

[Pickled Piper]

Try the bedding in procedure again. Nine times out of ten this cures it.

pp

[B19GRR]

Right, got the car up on jacks, couldn't see any darker deposit areas on the discs. When I spun the wheels I could hear the pads lightly rubbing but seemed pretty even all around, so nothing really conclusive. Out of interest how many revolutions of the wheel would be expected when giving them a good heave ho? I was getting around 3-4 turns. I'll give the bedding in procedure another shot and also get the balance checked again.

Cheers,
Rob

[paintman]

Spinning the wheel & counting the revolutions doesn't prove a great deal. Unless the wheel(s) are stiff to turn as a result of the pistons & pads not retracting slightly as the pedal is released which could indicate a braking system fault such as sticking or partially seized calipers.

If you have a dial gauge check the disc run-out.
I presume wheel bearings & all other items are in good order?
What have the garage that fitted the pads & discs said about the problem?

Edited by paintman on Sunday 8th November 17:04

[B19GRR]

paintman said:

Spinning the wheel & counting the revolutions doesn't prove a great deal. Unless the wheel(s) are stiff to turn as a result of the pistons & pads not retracting slightly as the pedal is released which could indicate a braking system fault such as sticking or partially seized calipers.

Yep, I figured it would just give me a quick idea if anything was majorly wonky.

paintman said:

If you have a dial gauge check the disc run-out.
I presume wheel bearings & all other items are in good order?
What have the garage that fitted the pads & discs said about the problem?

I had new (refurbed) calipers fitted last December and the suspension was checked over recently so it should all be good. I haven't spoken to the garage yet as I've been snowed under with other things, just wanted to double check things first to see if it was something obvious.

Cheers,
Rob

[B19GRR]

Just to wrap this up, I had the car in the garage on Friday and it turned out the near side front was warped. Not enough to see visually but measurable apparently. Anyway a new set of discs and pads up front done under warranty and all seems good so far. Hopefully just a manufacturing default in that one disc and the new set will stay true.

Cheers,
Rob

[paintman]

Good news. Always nice to know what a successful result was.