940 brake vibration

From a point at sea, to the circles of your mind, this is Tony Stanley:

People here have suggested that over tightening the wheel nuts promotes disc warpage - I've never had a problem on my 740. But warped brake discs are more likely to be felt through the brake pedal than the steering. I think I'd be having a look at wheel bearings or track rod ends.

Jack the wheel off the ground and grasp it at 6 and 12 o'clock; try rocking it. Ideally you shouldn't feel any play. Don't confuse it with steering or suspension movement. If there is any play, suspect wheel bearing.

Do the same at 3 and 9 o'clock. If you can feel movement, have someone put the foot brake on and repeat. If the movement is still there, suspect track rod end. If it disappears, suspect wheel bearing.

While it's possible that the disks are indeed warped beyond specs, what could be happening is the minor (below spec) warpage that is normal can be amplified if the bushings at either end of the strut stay (aka caster) rods are worn.

I remember reading somewhere, probably here, that heating up the brakes a lot, then sitting on the brake causes transference of material from pad to disk. Apparently if you look at your disk (both sides) you may see an outline of the pad left on the disk. Sort of like leaving an iron on a shirt I suppose. This can cause snatching. I wish I could remember the website.

Stuart.

Most of the time what I see is this effect caused by rust. Where the pads are sitting is protected, the remaining unprotected surface rusts. This is not a problem on a car driven every day, or stored in a garage, but can cause a really uneven surface on an infrequently driven car that sits outside, especially in the rear.