I've been working on getting my 1996 850 NA wagon to stop shuddering upon braking. This is especially noticeable when stopping from highway speeds. I changed the front rotors, pads and inner and outer tie rods to no apparent effect. The ball joints seemed okay both to me and the guy who did the alignment. So today I got the rear rotors turned, installed new pads and new emergency brake shoes. The shuddering seems somewhat different now, in that the brake pedal doesn't seem to vibrate, though there is still a considerable shuddering noise and vibration from the rear end upon braking.

I'm wondering about the rear rotors. When I picked them up from the local AutoZone, where I had them turned, it was clear that some of the rotor surface was still scored by rust. I asked the guy whether he would put them back on his car. He shrugged and observed, "They'll work." Well, the car does stop, so I suppose that's true, but this shuddering drives me nuts. Should I just suck it up and get new rotors, or is there something else I may be overlooking? Thanks.

 

Have you checked the calipers? And I suggest new rotors for the rear as it's not much $ and will put your brakes to 100%.

 

There is a chance that your rear shock mounts are bad or even your shocks.

 

Sorry for this duh moment, but I expanded my search a bit and found the many threads on half shims as a means of eliminating vibration on rear brakes. The old pads, I've realized belatedly, had full shims that were so rusted on the pads that I didn't recognize them as separate pieces. Unless someone has better advice, I think I need to get a set of half shims, install them and see what happens. Again, my apologies for a dopey initial search.

 

Check the thickness of the rotors if they are to thin, they will create a nasty vibration.

 

Been there...use the half shims. There are arrows, be sure they are pointed up.

 

For the sake of anyone blundering down this same path, the solution finally was to buy new rotors. Turning the old ones was a waste of money. Also, I started on this because of a shudder in the pedal that I assumed was linked to the front brakes. Turned out it was the rear brakes, but it was (at least for me) difficult to tell. The take home lesson here is that next time I'd buy new rotors right away and do the job once instead of twice.

 

yeah usually in the long run its better to just buy new rotors, and i had a rear caliper become sticky and did the whole shuddering thing, however i do not have shims on my rears and i have no problems since replacing the sticky caliper.

 

Also, never put old pads on new or freshly machined rotors. Pads and rotors do not wear evenly. There are peaks and valleys you can't see but when the rotors is put on a lathe you can see them as they are machined down. You may get rid of the pulse but you also have a minimum of braking surface until the pads wears down to the surface of the rotor.
Never under estimate the value of lubrication of the points where the pads contact the calipers and where the calipers are supposed to "float" to follow the rotor on those caliper mounts. Not making sure those points are clean and lubricated is just asking for the same problem again.
When you take your rotors in to have them machined try to talk to the person who is going to turn them and feel him/her out on if they know more than you. They need to be smarter than just knowing how to mount your rotors, turn the machine on and rip some metal from the surface and charge you. If they can't tell you you really should buy new rotors, yours should be fine, they can try but they wouldn't recommend it or some informed recommendation to you, you should go elsewhere. They should be fairly sure of the outcome before they chuck them up and if they didn't bother to measure them to make sure they were above minimum then all they want is your money and they don't care about it's quality. If you get indifference it's time to move on to a different person at that store or a different store. It's your brakes, they need to know what they are doing!

 

Had the same issue and installing the shims solved it. I do need new rotors but the shims took care of the violant humming sound.