Brakes: 855R Rear Brake Bias

[charlesdawest]

I have a 1996 850R Estate which i have owned for nearly 2 years. When i bought the car it had only just received new genuine front and rear disks the fronts being the 280mm. I found the car to be quite poor at stopping and prone to brake fade. After a few months the car developed an alarming vibration from the NSR. I replaced the calliper only to find the same problem immediately. After research on this forum i decided to upgrade the front and rear disks to Black Diamond grooved and drilled with black diamond pads, along with the front disks being increased to 302mm with calliper extensions. This immediately made a big difference to brake feel and stopping power, and brake fade kept to a minimum unless high speed extended breaking from over 100 to zero say but soon regains feel again. It also removed the NSR vibration which would indicate the original rears had warped as it only happened when the rear disks became rather hot. The car has run for 11 months before developing this NSR vibration again and is currently in the garage again. They have found the rear disks are working hard and have warped again, and are now being sent to black diamond for warranty claim. I have been told by the garage that these 850 estates have i higher rear brake bias due to its weight and so causing the rears to over heat? Is this correct? If so, now the car has the larger 295mm fronts as fitted i believe on the later V70R replacement to the 850R (so a greater front breaking capability) i wonder if these cars had a different front / rear brake bias? If so is it possible to replace the Brake Proportioning Valve to the later V70R? (I am not sure if either these cars have them actually), hence this post. I would be grateful for anyones input as don't want to fit new rear disks again under warranty only to find 11 months later i am back where i started. Thanks Charlie

[charlesdawest]

After much searching found the answer to the vibration problem. See below

By VOLVO 850 93-97 REAR BRAK... on the 26th of Jul 2010 05:51:19 PM Download | Raw | Embed | Report 1.BRAKE SHIMS -MINIMIZE RESONANCE VIBRATIONS REAR AXLE -1995 Volvo ...
2.Page 1 of 3
3.BRAKE SHIMS -MINIMIZE RESONANCE VIBRATIONS REAR AXLE
4.TECHNICAL SERVICE BULLETIN
5.Reference Number(s): GROUP 51, NO. 803, Date of Issue: August, 1996 Related Ref Number(s): GROUP 51, NO. 803
6.ARTICLE BEGINNING
7.NEW SHIMS TO MINIMIZE RESONANCE VIBRATIONS, REAR
8.Model(s): 1993-97 Volvo 850
9.Section: 5 - Brakes
10.Group: 51
11.Bulletin No.: 803
12.Date: August, 1996
13.REFERENCE
14.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.
15.SERVICE INFORMATION
16.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).
17.NOTE: Resonant vibrations are experienced usually when the car has new rear brake discs/pads.
18.The service manual referred to in this service bulletin is the Service Manual Section 5:
19.Brakes (incl. ABS and TRACS) 850 1992-On TP 5001201 or
20.Brakes (incl. ABS and TRACS) 850 1996-On TP 5002202.
21.PROCEDURE
22.1.Before replacing the shims the brake pads must be removed. See Fig. 1 . 2.Remove rear wheels.
23.http://www.ondemand5.com/mric/common/asp/printart.aspx
24.9/20/2008
25.BRAKE SHIMS -MINIMIZE RESONANCE VIBRATIONS REAR AXLE -1995 Volvo ...
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27.REMOVING BRAKE PADS
28.1.Push out split pins with a 3 mm (0.12") punch. See Fig. 2 . 2.Remove retaining spring. 3.Remove brake pads and shims. Use puller 999 2917-6 if brake pads will not come out easily.
29.CLEANING AND CHECKING
30.1.Clean brake pad contact surfaces in brake caliper. 2.Check piston boot. 3.If piston boot looks worn, replace it as a precautionary measure. 4.If the piston boot is damaged, recondition the brake caliper according to Service Manual section KD, (or PPP) "Disc Brake Caliper Rear, Recondition". 5.Press pistons back with a adjustable pliers (water pump pliers) or press tool 999 2809-5. See Fig. 3 . Take care to avoid damaging piston boot. 6.Check that piston boot is in the proper position.
31.INSTALLING THE SHIMS
32.1.Grease the shims on both sides with a thin layer of silicon grease, P/N 11613254. 2.The new type of shims has a cut-out. The shims must be installed with the cut-out facing down in the disc brake caliper. See Fig. 4 .
33.INSTALLING BRAKE PADS
34.1.Install brake pads. 2.Install one split pin and retaining spring first, then the other split pin. See Fig. 5 .
35.WARRANTY INFORMATION
36.Claims may be submitted under the New Car Limited Warranty when there is a documented customer complaint for brake resonance using claim type: 01.
37.OPERATION NO.: 51913-2 - Shims rear brakes installation.
38.TIME ALLOWANCE: 0.5 hr.
39.Fig. 1: Brake Pad - Remove
40.Fig. 2: 3 mm (0.12") Punch - Push Out Split Pins
41.Fig. 3: Water Pump Pliers & Press Tool P/N 999 2809-5
42.Fig. 4: Shims - Installed W/Cut-Out Facing Down In Brake Caliper
43.Fig. 5: Brake Pads, Install Split Pin & Retaining Sprint, Then Second
44.http://www.ondemand5.com/mric/common/asp/printart.aspx
45.9/20/2008
46.BRAKE SHIMS -MINIMIZE RESONANCE VIBRATIONS REAR AXLE -1995 Volvo ...
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