1996 850 R auto: terrible vibration when braking

[B234R]

Well, I had this trouble for a year, but now it´s unbeareable.

In february last year due to persistent ABS problems I put a remanufactured ABS module and a used pump motor. ABS codes were cleared and everything got right.

Four months later the car started to vibrate badly when braking, only at low speed (under 40 km/h- 25 mph). The shake came from the rear, the whole car vibrated noisily but brake pedal feel was normal. It only every now and then, so I got used to it. Last autumn I changed rear pads (non OEM, they were Brembos) hoping to solve the problem, unsuccesfully.

But since last week the vibration started to happen almost always, and not only at low speed, making the car undriveable. I noticed that it seems to shake when the brakes have reached a certain temperature, perhaps after a few minutes of city driving.

I took the car to the workshop, when I told the mechanic that I changed the ABS module and pump he deduced that they could be faulty, and he had to conect the scan tool. He will do it next monday.

But this afternoon I connected VOL-FCR to my car, and it didn´t pull any code...I noticed too that the vibration happens going forward, but the car never vibrates going backwards...

If you could help, I would be very grateful. I think the mechanic´s suspect about the ABS module and pump is wrong.

Greetings from Spain!

[tryingbe]

Front brake does most of the braking. If there is brake vibrating, it's almost always the front rotors/pads needs to be replaced.

[Bluevanacd2005]

When is the last time the rotors were changed?

Spenser

[B234R]

Thanks for your replays,

the vibration can be clearly felt from the rear end. I don´t know exactly when the rotors and front pads were changed, I bought the car to a friend two years ago and I have replaced only the rear pads (about 8,000 km ago).

I´ve reading a bit and it seems this could solve the problem, the famous shims
http://www.fcpgroton.com/product-exec/p ... gory_id/45

so I´ve ordered them to my local Volvo dealer and I´ll pick them up on monday. I´ll keep you informed.

Thanks!

[cn90]

Shims are used to reduce noise, not vibration.

Resurface your rotors and move on.

[Ben850]

My '96 wagon is getting a vibration from the rear as well. When I bought the car I was aware it needed brakes all around and I grabbed some basically new coated front rotors and new pads from a V70 at the yard, but could find no rears.

I had good pads to put on the rear. No good rotors but noticed the calipers both had sticky pistons. (rusty) A piston on one caliper was frozen I believe.
I presently have a vibration in the rear still while waiting to replace everything. Check for sticking calipers.

I have drilled and slotted rotors with Akebono Ceramic pads ready to go all around. I have two rear calipers to put on. The only thing holding me back is breaking loose the brake lines from the calipers. I have tried several penetrants. Torches. I will try the "Freeze-off" penetrant lastly before I order new factory rear metal lines and commence to tearing things apart.

As a side note, the Permatex synthetic brake lube is great for keeping the rear pads quiet. Use it liberally. It does not break down under heat. I haven't used shims on the sedan or the wagon. (I think Akebono pads actually have a backing that also keeps them quiet)

[B234R]

Well, it seems there is a Service Bulletin (Group 51, No. 803) about this vibration...

BRAKE SHIMS -MINIMIZE RESONANCE VIBRATIONS REAR AXLE
TECHNICAL SERVICE BULLETIN
Reference Number(s): GROUP 51, NO. 803, Date of Issue: August, 1996 Related Ref Number(s): GROUP 51, NO. 803
ARTICLE BEGINNING
NEW SHIMS TO MINIMIZE RESONANCE VIBRATIONS, REAR
Model(s): 1993-97 Volvo 850
Section: 5 - Brakes
Group: 51
Bulletin No.: 803
Date: August, 1996
REFERENCE
TP 5001201, Section 5, Brakes (incl. ABS and TRACS); 850 1992-On. TP 5002202, Section 5 (50, 52, 55, 59) Brakes (incl. ABS and TRACS); 850 1996-On.
SERVICE INFORMATION
If a customer complains of resonant vibrations from the rear of the car when braking at low speed (frequently when the brake discs are hot after repeated braking), the problem can be fixed by replacing the shims. A kit with a new type of shim has been produced for the rear brake calipers. The kit has P/N 272272-6 (kit contains 4 shims).
NOTE: Resonant vibrations are experienced usually when the car has new rear brake discs/pads.
The service manual referred to in this service bulletin is the Service Manual Section 5:
Brakes (incl. ABS and TRACS) 850 1992-On TP 5001201 or
Brakes (incl. ABS and TRACS) 850 1996-On TP 5002202.

My symptoms are the same, and the shims are very cheap, so I´ll begin changing these. I´ll keep you informed.

[Ben850]

Noting the 18+ year old bulletin, I would still allow for the newer technology of ceramics and synthetics to quiet the brakes. The shims are really no longer needed.

As far as the vibration goes, new rotors and pads, possibly refurbishing/replacing rear calipers.

[scot850]

Have you checked your parking brake mechanism for it sticking? Cables seize and cause the shoes to stick and cause vibration. The activating mechanism on the back-plate of the rear can also seize.

Jack the car up and see if either rear wheel is dragging. You could try backing off the adjuster and see if the problem goes away, before stripping it all down.

Neil.

[Ben850]

Have you checked your parking brake mechanism for it sticking? Cables seize and cause the shoes to stick and cause vibration. The activating mechanism on the back-plate of the rear can also seize.

Jack the car up and see if either rear wheel is dragging. You could try backing off the adjuster and see if the problem goes away, before stripping it all down.

Neil.

Good point.
The E-brake shoes had come apart inside both of my cars rear rotors. I am sure that will add to a vibration until you take the pieces out.
It is easy to figure out if the shoes had come apart. Lift the lever.