Well I've been doing some reading and I'm not sure if it's the ABS module or the modified rear shims I need to fix this problem on our 96 850 turbo wagon. When braking the cars shudders or vibrates and it feels as if it is comming from the rear of the vehicle, although I can't be sure. It doesn't happen every time. However you can make it happen by applying extra pressure when braking. My wife says you can feel the pulsating through the pedal. After much reading I've narrowed it down to either rear pads that are not seating properly, in which case the modified shims might fix it, or the control module for the ABS system is bad or is going bad. The brakes were re-done by me about a year ago and have worked fine until now. The pads have plenty of meat left on them. Is there any way to know for sure whether it is the rear pads or ABS module? Thanks for any replies.

I'm having a similar problem with my 97 850. I came up with an idea to narrow it down to ABS or mechanical problems. I removed the 30A fuse for the ABS pump/motor to prevent the ABS pump from running. The ABS light stays on now, which I expected. I drove it a few miles yesterday, and so far the vibration is gone. I'm guessing the vibration was the ABS system activating. I'll drive it for a few days with the fuse removed to verify, then I'll have to figure out how to troubleshoot to find out what's causing it to activate when it shouldn't.

I just went through all this. I had the same experiance. I had the wheels off three times. I first replaced front and rear pads , and rear rotors. It still shook. I then modified the rear shims. It still shook. I then changed all pads to OEM Volvo , I put in Volvo modified shims, and I put in new rotors on the front. This fixed the problem. BTW, I had new tires put on , and I think they didnt torque the lugs . I believe this caused it all. It cost me around 300.00 for a brake job I did myself.

I had the same problem and BOUGHT the modified shims from a local Volvo dealer. Fixed my problem completely. Also had brake squeal which the Volvo silicon grease took care of.

Slic
'93 850 GLT, 132K

I've got a 1994 850 Wagon and am experiencing the same problem. I am begining to think it has to do with the ABS module, and NOT warped rotors as my problem is intermittent as well. Like you most noticibly when extra braking pressure is applied...Hope we both get some answers... if not a least some ideas of where to look...

Brian
--
Noobie Volvo owner just wondering what took me so long!!!

Usually it is related to warped brake disks (AKA rotor). You will notice it more during heavy breaking. However, I am puzzled with the pulsation on the paddle.

Ronjon
'93 850

I considered warped discs, however, wouldn't the vibration be felt all the time at every application of the brakes to some extent? This is not the case. In this senario, the problem is intermittent. As a matter of fact, all my problems with cars seem to be intermittent. Why can't they just break and be done with it? Aargh!

You may need to read the on board diagnostic from the ABS socket. However, I heard that, some 850 years do not have on board diagnostics and you need a scan tool. 'not sure.

Ronjon
'93 850

Thanks for the reply Ron. I had a recent fuel problem with this vehicle and had autozone hook up the computer to reset check engine light and read codes. At that time, the brake problem had already started. The ABS light came on, then went back off after a while. I asked the tech at autozone for the codes and just the one for the rear O2 sensor was activated (the rear O2 has been setting of codes as long as we've had the car). I was hoping at this time the ABS had put out a code but it had not. The only indication so far is an occasional ABS light which normally goes off after a while. Check engine light is off for now. If I want it on, all I gotta do is romp on it one time and the O2 sensor will throw a code as usual...damn thing. Anyway, as far as I can tell, no codes from ABS. If you are talking about a computer hookup directly to the ABS module, I wouldn't know about that.

It may not be your problem but I had a similar issue with my 850R - where the rears would shudder violently - intermittently. It seemed to only happen when the brakes had warmed up, and when it happened the frequency of the vibration was much higher than what you get with warped disks. Also, the harder you pressed on the pedal, the worse it got.

Turned out the rear pads had glazed over. The guys that service the car ripped the pads out and roughened everything up and they have bedded in Ok after this, with no recurrence of the problem. Got it done during a service and didn't cost me a Zac.

You should be so lucky....


.

Hey Wolfman,
Thanks for the info and check this out. I hopped in the car today and decided to check it out myself. My wife had been giving me the info so far on the problem. I went out and had the car shuddering in no time. Felt some pulsating in the pedal like the wife said. Vibration all through the car. I was trying to determine if the anti-lock mechanism was coming on and causing the problem. I still was not sure. Then I decided to try something, as I drove, I applied the emergency brake a little. I figured if the rear pads where vibrating, this would effect the symtoms. If it was the antilock, this would not. So, I'm drivin around applying the emergency brake and the regular brakes with varying amounts of pressure, sometimes hard sometimes easy. Sometimes just the emergency brake. After much jick-jacking (that's a professional term) with the emergency brake I noticed I could not make the symtoms re-appear no matter what I tried. So I drove it around for about a half hour applying the brakes at different levels and NOTHING. Worked like a charm. So, if I'm luckier than you, this is my diagnosis: The rear brakes where glazed or not properly seated or the rotors where dirty/rusty, something to that effect. Me driving with the emergency brake halfway pulled in spurts either re-seated them or knocked the glaze off or cleaned the rotors. Whatever the actual cause was, this "treatment" fixed it. So, if I don't return to this thread, it means the symptoms did not return. If the symptoms do return, I'll come back and have some crow pie!

Good luck wih your fix. I must say, when I had the shudders the problem was intermittent so I would think it had gone away and then it would come back to bite me after a while. Having had a couple of sets of warped rotors, I would say that the characteristics of the shudder were clearly different from warped rotors - much higher frequency and more violent, to the point where it felt sometimes like the back of the car was shuddering and dancing.

I feel I contributed to my problem by not using the brakes firmly enough and by not bedding them in when the new pads + rotors were fitted. BTW - my current rear brakes are not OEM items, they are aftermarket rotors and low-dust pads. This may also contribute in that there is less of the natural wear (and freshening up of the contacting surfaces) than what one would have with the original parts.

bp238,

Your e-brake is actually a mini-drum assembly inside the rear rotor hat. The method you desribed would not clean off your rear pads/rotors. Maybe you e-brake has something to do with this problem?

Just a thought.

-Brad.

Could be a problem with the e-brake. I drove it again this evening and still no problems....keeping my fingers crossed.

Well, dam. It's back, but not as bad. Seems if I work the brakes a little harder I can ease the symptoms but we still have a problem. I'm thinking the shimm kit is the best place to start. I did notice once, a quick pulsing in the pedal like the ABS was acting up. Just felt it once though. It's like the shuddering might trigger the ABS every once in a while. Maybe if I can fix the shudder (if it's the shims), the ABS will be OK. My last resort will be the ABS module.