BMW R850R: Rear Brakes

The below repairs, replacements, and what-not have all been done by me on my 1997 R850R. Many of the procedures can apply to other BMW bikes of similar vintage, primarily the R1100R and to a certain extent the R1100GS. Do not attempt any of these procedures unless you're confident in your skills - however limited - as a shade-tree mechanic. Don't send me hate mail if you mess something up!!

Replacing Rear Disc Brake Pads

Tools Needed: 5, 6, and 8mm hex wrenches or sockets; hammer & drift or punch; needlenose pliers; large flathead screwdriver; large syringe or turkey baster; rags
Parts Needed: one set (kit) of rear brake pads, BMW Part # 34 21 2 335 465; DOT4 brake fluid (if necessary)

Note: You'd normally think the brake disc would be connected to the wheel; not so in this case. On the R850 & 1100R bikes, the rear disc brake is actually connected to the DRIVE, not the wheel - so you can perform this maintenance item with the wheel in place! Be aware that brake pads and brake dust can be VERY harmful to your health - don't inhale brake dust, don't put brake-dirtied fingers in or near your mouth or nose, and clean your hands thoroughly when you're done.

Check this picture for locations of some parts mentioned in this procedure.
Full size (1600x1200) versions of these pictures reside here.

1. Remove both seats and the right side hard case.
2. Remove right side panel - you'll need at least the 5mm hex wrench here to remove the bolt securing the side panel by the brake light. If you have the side case rails and the accessory rack on your bike (like I do), there are TWO 5mm hex bolts (over & under) as well as a black spacer that goes BETWEEN the side case rail and the rack rail on BOTTOM bolt. The front bolt of the side case rail is a 6mm hex. Be careful of the small press/snap fittings on the BOTTOM of the side panel.

3. Wipe off any debris/brake dust from the disc.
4. Visually inspect the disc for deep scratches, chips, or other damage. If it shows damage of this type, it should be discarded and replaced (by a qualified mechanic if necessary).
5. Using an 8mm hex wrench, remove both bolts securing the caliper to its mounting points. Being careful not to twist the brake line, rest the entire caliper assembly on the right rider's footpeg.
6. Visually inspect the mounting bolt threads as well as the threads they secure to. If you detect any damage, get thee to a qualified mechanic.
7. Clean the outside of the rear brake fluid reservoir and remove the cap (you may have to hold the body secure with your other hand - it's just in a press fitting).
8. Using your large flathead screwdriver, gently and SLOWLY pry the existing brake pads apart until you can move them no further. They should slide smoothly and relatively easy, though it will take a decent amount of pressure to get them to move. Don't worry about damaging the pads - you're replacing them, remember? You should use a simple twist-pry motion to initially get them apart, then move on to full-on prying. Watch the fluid reservoir and DO NOT ALLOW IT TO FLOW OVER. As you separate the pads, brake fluid in the caliper and the line will be forced back into the reservoir. If it looks like it's in danger of overflowing, use the syringe or turkey baster to remove some brake fluid.
9. Once the pads are as far apart as you can get them, use the pliers to remove the E-clip/C-clip/circlip or whatever is securing the end of the brake pad locating pin.
10. Using the hammer & drift, unseat the locating pin and, once it's free enough, remove it and wipe it clean. I had the best results - being without a helper - by resting the caliper on the footpeg and just taking my time.
11. Remove the worn pads, noting that one end has a tab and the other has a hole (for the locating pin). Make a mental note of where that little tab goes. Discard the worn pads safely (I put them in the box the new pads came in & put that in the trash).
12. Place the new pads in the caliper; be sure to insert the tab completely into its housing. You should get some resistance when you press down on the pads - there's a spring under them (from how you're looking at them anyway) that helps keep them in place.
13. Reinstall the locating pin - you will most likely have to use your thumbs to get the holes lined up (due to the spring) and wiggle things around a bit. The pin should slide right in once it starts moving. Tap the end of the pin with the hammer to fully seat it.
14. Reinstall the E-clip/C-clip/circlip.
15. Reposition the caliper on the brake disc. You may have to wiggle it back and forth a little - using your thumb to hold the non-piston side pad in place will help. GO SLOW and don't damage the disc!
16. Reinstall the 8mm hex bolts. Remember how tight they were when you took them off? Make them THAT TIGHT again! If you have a torque wrench, the proper torque for these bolts is 40 N-m or 29 ft-lbs.
17. Refill the brake fluid reservoir with FRESH DOT4 BRAKE FLUID if necessary - NEVER re-use removed brake fluid!!
18. Using your hand, apply the rear brake several times until the pads seat firmly against the disc.
19. Reassemble the side case mounting bar; be sure to get the spacer in the right place if your bike has the accessory rack on it like mine. Remember - long 5mm bolts in the rear by the tail light, short 6mm bolt in the front. Don't forget that the rearmost hole of the side panel has the top 5mm bolt through it!
20. Finish reattaching the side panel and install your seats.
21. CAREFULLY test ride your bike, firmly applying the rear brake. If you detect any "hitching" or "dragging" feel, IMMEDIATELY stop your bike and go back through ALL the reassembly steps to ensure you didn't miss anything.
22. Clean your tools and put them away; safely discard any removed brake fluid as well as the worn brake pads.