Brake judder - opinons please

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I have significant brake judder, noticeable at speeds of 60+. The brakes are fairly fresh and look ok to me, though I don't know what make they are. I'm pretty sure it's the rears since there is no vibration in the steering wheel.

The pics below show a front disc versus a rear. The markings are continuous on the fronts but the rears have what look like definite start and end points. Rears are in the top pic.

Any thoughts before I replace them?

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helix402 said:

Discs in second pic look worn out. Not necessarily the cause the off the brake judder however well worth measuring and comparing to minimum thickness to check.

I see what you mean but think the angle is misleading. They're fairly new.

It's a 335i if it helps. Suspension problems are unlikely since the shocks were all replaced not so long ago and it all looks fine. Just gone through the MOT.

I was considering getting them skimmed but the cost isn't that much less than replacement. May still be the best option though I guess.

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Fore Left said:

I had the same on my 330i. Horrendous vibration at 50mph+. Turned out to be a sticking rear caliper. Take the car for a good run, stop and flick water on the disks. If any boils, that's the culprit.

A constant vibration or only under braking? I don't understand why a sticking caliper would cause a vibration but what to I know? I don't think that's the problem anyway as they turn freely on the drive.

Thanks for all the comments, though I'm none the wiser currently. I'll either replace or skim and report back. Probably skim as they still look like new on the rear.

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HustleRussell said:

That's a bad idea! A number of people, including two with direct first-hand experience of this problem on BMW 3-series, have said that this problem can be caused by a sticking brake caliper. Guess what happens when you replace or skim the discs and fit new pads without properly investigating the cause?

If the caliper isn't moving freely it drags on the disc and gets very hot, when the disc, piston, pad backing etc etc gets hot it expands which causes the brake to drag more, this causes it to get hotter.... and then you leave the motorway and stop at the lights, the pad welds itself onto the now stationary disc leaving a nice patch of friction material on the disc, rinse and repeat...

I'm not ruling anything out but in the absence of a conclusive diagnosis I'm minded to start with the cheapest/most likely causes. I first noticed the issue a couple of weeks after I bought the car, since when I've done about 8000 miles in 10 months. It hasn't got any worse and the discs and pads look new and both sides look the same. A sticking caliper seems unlikely and it won't be the end of the world if I waste £80 on skimming.

I've had a sticking caliper before on another car. It was obvious, I could feel it once it got bad and the pads on the caliper were shot.

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I thought I'd update this since I've finally gotten round to getting it looked at and somebody may find the info useful in future.

I took it to a garage that has this kit:

http://skimmydiscs.co.uk/

They put it on the MOT brake tester and found a vibration on the N/S rear with brakes applied. So they skimmed both rears and the judder is 100% cured. I don't know what caused it so hopefully it won't come back.