Julian
My car has an intermittent VERY serious vibration under braking. It doesn't happen all the time, and when it does I can usually let off/get back on the brakes a few times and it will go away, but it's something I really need to sort out for safety. It seems to happen much more in hot weather. It's like driving on the strip at the side of the highway, but MUCH more severe. It's really the whole car shaking, not a vibration through the pedal like you get from warped discs.
I have tried driving with the abs module fuse pulled and it still does it. I have a vague feeling it's coming from the rear, but hard to tell since the whole car vibrates so badly.
So I'm thinking about taking the rear wheels off and checking out my brakes, but beyond just looking for worn pads or anything clearly broken, I'm not too sure what else I should be looking for. Any tips for what to check?
Jamest5r_
How olds the brake fluid?
Julian
I haven't changed it in the couple of years I've had the car, but would that cause the severe vibrations? It feels like it has to be something pretty serious
timbo
i had an issue with my 850 wagon where the cheap brake pads in the rear would overheat and cause the whole car to vibrate violently. i put new rotors and decent pads in and it fixed it. If your brake pads are overheating you will see heat cracks in the friction material and the surface of the pad will be smooth like glass.
post some pics of the pads and rotors when you have the wheel off.
Rolvo
+ 1 to changing brake pads. I too got a trembling/tram-lining vibration from the rear after a while after warming up - turns out it is a known issue and shims were the solution. I took the pads out and pads were 50% worn (already had shims fitted) so replaced with new pads (bendix) and using original shims and all good since .
Julian
A few pics attached. Pads seemed to have reasonable thickness left, and had the shims pictured on each pad.
I also looked at the front which seemed ok except for the dust seal being partially popped out. I'll have to replace this with a new one since it seems to have stretched over time and now has too big of a circumference not to pop right back out of its groove in the caliper
carnut222
Hmm, any chance the rubber dust seal you mentioned could be getting sandwiched between the pad and the piston? That could cause a problem!
Julian
I don't think so, since the pad has three metal tabs that hold it to the piston and the rubber seal sits pretty close to the caliper still. I did clean out the area behind the seal, although it didn't seem that dirty.
Ex850R
The shim is broken. Don't use it.
Lots of calipers I have seen on P80s don't have the shims and only some new pads have them.
Ex850R
The pad looks worn in wedge shape from that half shim, get new pads.
carnut222
That shim is not broken. Some are designed that way.
Julian
What do the shims do? And should I be putting them back in or are they not necessary?
carnut222
They are intended to keep the brake pads from vibrating causing brake noise. I would reinstall the shims as per the factory and make sure those asymmetric ones are fitted the correct way around (I don't know what orientation they're supposed to be in). Usually you smear some brake paste on both sides of the shim, and on back of pad, when installing. Make sure it's the correct stuff - obviously not grease! :)
Ex850R
Most of the P80s I have had haven't had the shims. They help with squeal stopping.
Half the pads I've put in didn't have them.
Have never got around to grease either!
Julian
Ok, so I bought new pads today and installed without shims. The guy at the brake parts shop said they wouldn't be necessary since the new pads have rubberised backing. I have the shims sitting in the garage in case I find they're needed.
I only went for a brief drive but the vibration didn't happen. Will drive a bit more this afternoon and see if it stays gone.
My theory is that maybe the shims sometimes got stuck on those pins the pads sIide on and caused vibration, so I have sprayed a bit of lube on those too.
Julian
So I was driving today, and the vibration came back! It wasn't as bad as previously and not as frequent, but still there.
I took the brakes apart again, and put the half shim back in. After doing a bit of reading on this it looks like this was volvos solution to the vibration issue when it arose. I made sure I scrubbed and cleaned the slide pins, shims, spring contact surfaces and put a thin coating of nickel anti seize lubricant on them to try to stop anything binding. I've driven a small amount since doing it and the vibration has not yet happened. Fingers crossed.
At the moment I'd recommend anyone with similar problems get fresh pads, scrub the pins, springs and shims (pick up some half shims if you don't have them, I believe they are meant to be installed with the full end down) and lubricate the contact surfaces (with the obvious exception of the pad friction material) with a high temp lubricant.