OK, so here it is, all the Do’s and Don’ts for changing out the Final Drive.
The usual disclaimers apply. For instance, do you really want to attempt mechanical work that puts your ass on the line, in more ways than one, risks damage to some very expensive parts, may result in premature drive line failure, and may disable your scoot for weeks or months while someone else cleans-up a costly mess? It is therefore stated that the author hereby recommends that each person performing work do so based solely on the procedures published by BMW in the R1150GS Repair Manual.
All supplemental information and comments are provided for background understanding only and are not to be relied on by any individual performing actual mechanical work. Proceed with caution and at your own risk.
Parts and Supplies Required (as specified by BMW):
* Replacement Final Drive Unit including Pivot Bearings.
* Drive Shaft Boot Zip Tie Fasteners
* Staburags NBU 30 PTM. Spline and Bearing Grease
* Loctite 270 Maximum Strength
* Brand-name hypoid gear oil, SAE 90, API class GL 5 (250ml)
* Large Torque Wrench, >= 200NM (for Fixed Pivot)
* Small Torque Wrench, <= 5NM (for Floating Pivot)
* 30mm Socket (for Fixed Pivot)
* 16mm Socket (for Reaction Link)
* 12mm Allen with adaptor to fit Small Torque Wrench
* Misc. Standard Sockets, Adaptors and Drives
* Long Reach Flat Screw Driver
* Heat Gun or Propane Torch
* Packing Strap (to tie off center stand)
* Scissor Jack (to support rear swing arm)
* Flash Light
The Official BMW Procedure in plain English
Do’s and Don’ts: Wrenchin’ Retard Tips, Comments & Additions in Italics
Rear Drive Assembly Diagram from BMW 1150GS Repair Manual.
1. Drain the drive oil.
It need not be drained but will save spilling it later cause both the ABS port and top vent leak.
2. Remove the rear fender flap (if not gone already).
Now is a very good time to strap the center stand to the front wheel.
3. Remove the brake caliper and ABS sensor and secure.
Note washer on rear caliper bolt; front bolt uses the ABS eyelet as a washer. Do not allow brake pedal to be depressed with caliper removed. You might slip a wood shim between brake pads to avoid this potential.
4. Remove the rear wheel.
Put trannie in gear to prevent wheel rotation.
5. Loosen the rear reaction link bolt (paralever strut) but don’t remove.
Support rear swing arm with Scissor Jack behind trannie on left side of swing arm.
6. Clip the zip ties and peal the rubber boot to the rear.
7. Heat (max 120 C.) the floating bearing stud (left-hand 30mm lock nut and 12mm stud) to release loctite, loosen but don’t remove.
A heat gun is best (not a hair dryer). A propane torch will work fine at a medium/low setting. Apply flame only to the bolts to avoid melting finishes or the rubber boot. You can loosen the bolts while applying heat but be sure the loctite is melting to avoid potential thread damage. Actual measuring of the temp should not be required. The heat is only needed to melt loctite and has nothing to do with pressed fittings.
8. Same on fixed stud (right-hand 30mm bolt).
Remove the locknut first! Then loosen the left stud with a 12mm allen key.
9. Remove reaction link bolt; remove left stud; remove right stud while supporting drive unit. Pay attention to inner bearing race on each side.
When pulling the studs, be careful not to let the bearings crash on the edge of the bolts. EZ does it.
10. Slide drive with pinion shaft (U-joint section) to the rear to disengage from drive shaft spline.
Slide the drive all the way out, then down. If your going to store the drive unit. Zip tie the inner bearing races after the drive is out to prevent losing them.
Now is a good time to remove the rear shock. This is not required, but will allow more upward rotation of the drive shaft for easier alignment of the drive splines.
Photo shows shock bolt being used to support drive shaft perpendicular to transmission.
Diagram shows proper phasing of drive shaft. The U-joint lobes are mirrored on each end of the shaft.
1. Clean and pack roller bearings with grease.
The better the bearings are cleaned and the more grease is worked into the cages, the longer they will last. If the bearings are used and have pitted races, show roller indentations, or have blued due to over heating, replace the bearings. Use any good solvent to clean the bearings. Do not remove the roller cages or bearings from the outer race. The inner race comes out easily and should be removed for cleaning and repacking. New bearings do not require cleaning or repacking. If they drop or become separated later, re-clean and repack unless you’re sure no sand or metal has gotten in.
Overheated bearing race has blued and shows indentations from being over torqued previously.
2. Clean and coat drive shaft and pinion shaft splines with grease.
Now is when you “Phase” the U-joints. Before greasing the splines remove the pinion shaft (U-joint section) from the drive unit by carefully prying outward with a large, flat screw driver. It should pop fairly easily. Then align the splines with the drive shaft to phase the U-joint. The position of the lobes to the front of the U-joint must match the position of the rear most facing lobes of the drive shaft U-joint, deep with-in the housing where it meets the back of the trannie. Use a flash light and move the drive shaft up and perpendicular to the back of the trannie to see the exact position of the lobes. The splines only meet one way and the U-joint should be turned 180 degrees if they don’t match up. When matched, mark a convenient spot on both pieces with a scratch or indent. Remove the pinion shaft and grease both ends and both sockets. I don't use the BMW grease cause it's hard to find. I used a Moly type, high preasure, CV joint grease. Insert the shaft into the final drive and give it a soft hammer blow to reseat. Make sure it is fully seated and does not pull back out by hand.
Pinion shaft “pops” free when pried from Final Drive with a long, stout screwdriver.
Pinion shaft phased with drive shaft. Note circular U-joint fitting can be visually matched by looking
deep into the shaft housing at the right angle with a bright light.
3. Place rubber boot in position on drive unit.
Don’t forget to do this or feel stupid in about two minutes.
4. Clean both bearing studs with acetone and apply high strength loctite to threads of each stud.
Cleaning the studs and the housing threads is important. Particularly the left, or floating stud. When clean, test the studs in the housing to be sure they screw all the way with no resistance. If rough, clean again and run from the inside out to de-burr any rough threads. The left stud must turn freely to properly preload the tapered bearings. The floating, or left stud, preloads both sides. Apply a single bead of loctite, lengthwise on the right, bolt. I am told (via the Pelican R11S Forum) that BMW has issued a service bulletin recommending that the left stud not be treated with loctite to facilitate later re-torque. I have not seen the bulletin or verified it with a dealer.
5. Align U-joints and slide final drive splines into drive shaft socket.
To insert the splines matching prior marks, the drive shaft should be held parallel by carefully inserting a screwdrive through the right pivot hole in the drive shaft housing. Use the screw driver to hold up the shaft while moving the housing into place.
6. Install right, fixed stud bolt to engage inner bearing race (Do not allow stud to pinch the outside edge of bearings) finger tight.
The right pivot stud must line up straight through the bearing race. If the stud pinches the bearings or the plastic bearing cage, the bearing is ruined and must be replaced. Make sure the right stud has seated before installing the left. To replace bearings, heat the housing lightly and drive the bearing out with a socket and extension that closely match the outer diameter. Replace in the same fashion. Do not try to extract bearing races with a pry bar or screw driver.
Pivot bearings can be pressed free with a properly sized
socket and extension. Light heat may be applied if needed.
7. Similarly, install left floating stud without tightening.
The left stud should only be run about half way into place. You can hand screw all the way in and then back out about five turns if you want.
8. Torque right stud bolt to 160Nm. (118ftlb.)
When the right stud is torqued, the left stud must not fully seat or the bearings will be over-loaded and ruined. If the left stud is tight after torqueing the right side, you’ve done it wrong and need to re-inspect the bearings carefully. Replacement likely.
9. Tighten left floating stud (without lock nut) to 7Nm. (5.2ftlb.)
The left stud is torqued lightly (5ftlb.) to pre-load the tapered bearings. Like a steering head. The drive should pivot evenly, and without snags. If the bearings are under torqued, slight rear wheel wobble will result. If over torqued, they will over heat and wear rapidly. Since 5 ftlbs is difficult to set on a large bolt, most mechanics do this step by feel. For a torque wrench to work, the threads must be very smooth and any locktite must be very soft. A little too tight may be better than a little too loose, but way too tight is not OK.
10. Torque lock nut (left) to 160Nm.
Make sure the stud does not rotate while torquing the lock nut.
11. Install reation link bolt finger tight.
Put the shock back on now. Top bolt: 50Nm (37ftlb.). Bottom bolt: 58Nm (43ftlb.). Do not tighten the reaction link fully at this time.
12. Replace zip-ties on rubber boot.
You don’t need OEM parts. Any zip ties long enough will do.
13. Reinstall rear wheel with two stage torque, 72Nm (53ftlb.), then 105Nm (77ftlb.).
I place a wedge under the wheel to raise into position. Alternate bolts.
14. Reinstall brake caliper bolts. Torque to 40Nm (30ftlb.) and install ABS sensor.
Don’t forget the ABS shims. Ease the caliper on to avoid opening the pads too wide. Check brakes and bleed if required. Since the caliper is going on the same rotors there should be no reason to adjust the ABS gap, but it should be checked.
15. Load 87kg (187lb.) onto free standing motorcycle and torque reation link bolt to 43Nm. (32ftlb.)
A heavy person sitting on the bike is required for this step. It is important to preload the strut, or it won’t operate in the correct flexibility range.
16. Fill final drive with 250ml gear oil.
Fill the drive to the bottom of the filler port threads. I use BMW synth. Some folks say to break-in a new drive with conventional gear oil. I don’t agree.
Test Ride and Laugh Your Ass Off!
When all else fails……