Hi

I have a very strange brake problem on my 850 that neither I nor the mechanic that works on my car can figure out. I had new front OEM size cross-drilled rotors installed along with some KVR brake pads about a month ago. I broke them in, as instructed, and as far as I can tell, they work wonderfully and very smoothly. But recently, I've taken a new route to work that has a steep descent that requires a good amount of braking and that is when I first felt some vibration. It only occurs on this stretch of road and I have yet to duplicate this vibration on any other surface and/or road around where I live. I don't feel the vibration particularly in the steering wheel or anything, just some noise and then the whole car seems to quiver/vibrate--can't even accurately point out that it is even the front brakes causing it. And it only occurs at very very low speed, by my accounts, the noise & vibration kicks in at the last 2 to 3 seconds of braking and by that time, I've slowed to practically a crawl. Today I had my mechanic re-torque the lug nuts (to make sure they are torqued within spec) and visually inspect the brakes and he could not find anything at fault. I hope the rotors aren't warped and my mechanic assures me that warped rotors would be more obvious and would happen at all speeds. Can anyone offer me some help on this one?

This sounds like a classic problem of warped rotors. Often temperature has a large effect on rotor vibration. Slight warps may only be detectable once the rotors get warm. In your case they may be the rears rotors too. Do a simple run-out test on the rotors when they are hot.

My suggestion is when they wear out replace them with the stock Volvo rotors or go to ATE's slotted rotors if you must have the extra performance. Volvo brakes are and have always been overbuilt and are the most reliable combinations that I have seen (except for the late 700's). Cross drilled rotors are not as good as they seem. Often the holes allow cracks to occur when but to the extreme, and they are less reliable than some others. If these rotors are warped, do not machine them straight, just replce them and ensure that the wheel nut are tightened equally.

Andrew P

If your front rotors were warped, normally the steering wheel would quiver from side to side when braking. The vibration of the car (vibra-bed) is normally caused by the rear rotors. If your rear rotors and pads are close to new also, you might try the cut out shim kit that Volvo sells to help with the rear brake vibration. Your discription of the vibration and how to cause it doesn't sound too bad. When really bad a shot trip up the freeway with 5 to 6 pedal applications will normally get the car shaking good on demand, and it will continue until the rotors cool down. Try the cut out shims and let us know how it went.

Hey Rich K. thanks a lot for your input--much appreciated. So it's possibly the rear rotors causing the vibration? But those haven't been touched, I only had the front pads and rotors replaced last month. I'm actually still on the original rear rotors although the pads have been changed before but that was quite a while ago (at least 6 months or even a year ago). But thanks for pointing that out, I will do some more investigating and take a good look at those rear brakes now.

I have noticed on numerous occasions shortly afyer replacement of front rotors and pads, the rear brakes start to have vibration problems as you describe. The cut shims Rich mentions usually corect the problem. They are stainless steel and have a corner cut out of the bottom/front.

This is certainly getting stranger by the minute! Would you happen to have any explanation or theory as to why replacement of the front rotors & pads would cause such a vibration problem with the rear rotors? They seem to have no connection whatsoever considering that they are on opposite ends of the car. Also, these cut out shims--Volvo service dept. sell these as a kit? How much are they roughly and how much would it cost to get them installed?

Thanks again everybody.