aggarcia Posted September 27, 2011 Report Share Posted September 27, 2011 For a 97 Volvo 850R, I have had a issue with rear brakes causing a horrible vibration that shakes the car when braking from less than 25 mph to a complete stop. The vibration shakes and rattles the whole car. I have owned my 850R for 15 months. This problem existed since i purchased it, but only showed itself after 1+ hour in stop and go traffic. When I got the car it only made a slight vibration and was not that noticable. The more I worked on car to improve it the worst this vibration has gotten. What I have done to date - I have replaced the rear calipers with rebuilt units, flex lines, new Brembo rotors, Poterfield R4S pads, the full and half shims, brake goo, new hardware, rear sway bar, MattyMoo Trac/ABS unit, and bleed the brakes. The wheels are tires have been replaced and swapped with on effect. I have used the diagnostic troubleshooting on Matt's website and everything tests ok. The whell sensors ohm out fine, and the abs pump ohm out ok. I had my wife drive the car around, and brake while I could see and hear it and the rears can be seen to grab and roll, grab and roll. While driving and this vibration can be seen and felt. If you are really braking aggressively the pedal travel is longer. Since the vibration is in the rear, what controls the pressure to the rear brakes? The only two parts that I have not replaced is the brake master cylinder and the ABS pump. I did find a 97 ABS pump from a car with TRAC/ABS at the local junk yard, but I want to be certain before replacing with a used part. Any ideas? Any help is greatly appericated. AG Link to comment Share on other sites More sharing options...
dimka18 Posted September 27, 2011 Report Share Posted September 27, 2011 Mine does the same thing.. Let me know if u figure this out? Im stumped my self.. Started to happen when i installed some cheap rear brake pads.. Also squeak when i brake while going backwards. Link to comment Share on other sites More sharing options...
Gilhuly Posted September 27, 2011 Report Share Posted September 27, 2011 I have a lot of experience with this issue and I've never not been able to fix it yet. Did you say that you have both solid and half shims? I would get rid of the full shim and use only the half shims. If your pads are not new, pull them and figure out which way they are wearing crooked. They will be slightly slanted. You want the fat part of the pad on the trailing edge (or top) of the normal forward rotor rotation. This is what the half shim helps accomplish - more piston pressure on the trailing edge(installed top) of the pad and less on the leading (bottom) edge. The vibration is a grab and release that occurs by the leading edge grabbing and releasing many times a second. I don't think it can be seen. The way to deal with pads you've had for a while that still have lots of life in them is to remove them from the caliper and switch them inside/out, making sure the shims are rearranged to reinforce the trailing(top) edge. Hang with me on this. It will work and your wife will look at you admiringly for about five minutes before forgetting you've ever successfully fixed anything. I use silicone grease on the pad backs and on the shims as well. Link to comment Share on other sites More sharing options...
FCP Euro Posted September 27, 2011 Report Share Posted September 27, 2011 From what you have said, I am thinking it is not the brakes, but an issue with the rear suspension. How do the bushings in the delta arms look? Link to comment Share on other sites More sharing options...
aggarcia Posted September 27, 2011 Author Report Share Posted September 27, 2011 The pads and rotors have been replaced since I purchased the car. I have tried both the full and half shims and neither fixes the issue. i have used lube on the brake pins and the orange anti-rattle noise goop on the back on the pads. I think the noise has gotten worst with the more aggressive Porterfiled pads. I first it would take several blocks or until the car got warm before the noise happened. In the rear I have install H&R rear springs, Yellow Koni shocks, and the IPD 25 mm swaybar. The car has been to the alignment shop several times looking for a possible suspension cause of the vibration. The alignment shop could not find anything wrong with the suspension. I checked the delta link bushings when doing the rear sway bar. I had though about the rear suspension also, but would all the delta link bushings go bad at the same time to cause the rear vibration? If the bushing were that bad you would think the car would not hold alignment or show so strange handlling effects. AG Link to comment Share on other sites More sharing options...
Gilhuly Posted September 28, 2011 Report Share Posted September 28, 2011 I would go with volvo pads on the rears and reinspect the way you've installed the half shims and the way the pads are wearing. I think if I had your car on my lift for a half an hour your problem would be in the past. This is a very common problem. Either a particular has it or it doesn't for some reason. I've never seen this not be fixable. Being in Houston does make it worse, though I will admit. High heat and humidity does bring it on. Link to comment Share on other sites More sharing options...
aggarcia Posted September 28, 2011 Author Report Share Posted September 28, 2011 I will try playing with the Porterfield, stock pads, and half shims this weekend. Since I like my cars to stop and at some point have taken them all on the race track, the Porterfield pads have never let me down. The issue is not noise, I could live with a little brake noise. It is the whole back of the car vibrating when braking speed gets to less than 25 mph to a complete stop. I have a feeling that brake pads will not fix this issue. I will let you know what the out come is next week. AG Link to comment Share on other sites More sharing options...
Gilhuly Posted September 29, 2011 Report Share Posted September 29, 2011 Believe me, I know EXACTLY what you are describing. It is absolutely intolerable. Link to comment Share on other sites More sharing options...
rmorse Posted September 30, 2011 Report Share Posted September 30, 2011 It's a shim issue. Link to comment Share on other sites More sharing options...
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