I had the same kind of shake. I removed the read brake pads and modified the shim by cutting out a square in one of the quarters. Since then I never get the shake. I still occasionally get the ABS light. The dealership also told me I needed a pump, but from what I have read in other posts, that is a common code when the card fails.

For me, the shaking was unrelated to the ABS light.

The instructions for modifying cutout are on bay thirteen

http://www.volvospeed.com/850rbrake1.htm

Go to the second page.

If you need a used ABS pump pls let me know because I have one sitting around.
It came bolted to my ABS Controller, but since my car only needed the ABS Controller replaced I still have the pump sitting here. Make me an offer.

e-mail me letsfroggy at yahoo dot com

Could be just a speed sensor on one of the rear wheels, either dirty or broken wire or just a bad sensor. There should be a code stored if the ABS light came on. You just need to find a shop that has the scan tool to read the ABS codes on a Volvo, not easy to find. Good luck.


Mike
'95 850T

Whatever you do. DO NOT Replace or open the hydraulic block.

Vibration on the rear brakes is not always associated with a malfunctioning ABS system. I have a 98 V70, 96 and 95 850. Once in a while, for no reason at all I get the vibration/shatter in the rear breaks, this problem is not related to the ABS system. Activation of the ABS system by a defective ABS control unit if felt mostly on the break pedal.

The problem with your ABS sytem is most likely a defectiv ABS Control unit, all of the ABS units will eventually fail. That is what everybody is referring to when they tell you to buy a used one.
Used units will also eventually fail as well as a brand new one from the dealer.

Your problem is very common and easy to take correct.

Here is more information on Volvo ABS issues.
Vitor's web page
Click on the ABS / TRACS Repair link.