Oilhead Rear Drive “Big Bearing” Replacement
A great thread with images can be found on Advrider.com
Date: February 17, 2006
Author: Ron Wiebe – BC, Canada
I’ve just finished replacing a failed rear drive “big bearing” on my 2001 BMW R1150GS and wanted to share my experience with fellow riders and DIY mechanics.
Acknowledgments
First, a huge thank you to Dick Fish, whose detailed post on BMW rear drive bearing repair was an invaluable resource. Dick is an accomplished rider—former ISDE competitor, top 10 Iron Butt Rally finisher, and participant in the Ultimate North America Challenge. His tip to change the rear drive oil at every engine oil change helped me catch the problem early.
Early Detection Saved My Final Drive
Thanks to routine oil changes and vigilant inspections, I noticed shiny metal flakes on the magnetic drain plug—a telltale sign of bearing failure. This is different from the usual gray sludge you might see. If you spot shiny metal flakes, take it seriously. Fortunately, my large oil seal remained undamaged due to the early catch.
Let me be clear: it’s not a matter of if your rear drive will develop this issue—it’s when. In our small BMW club (just 50 members), five bikes had this failure last year alone.
From what I’ve seen, there’s no obvious correlation to mileage. It’s more likely related to heavy loads (e.g., two-up touring, lots of luggage) and shock loading (like potholes or road debris). Solo riders may be at less risk.
Step-by-Step Repair Guide
⚠️ Note: If you’re not confident in performing mechanical work, consult a qualified mechanic.
Tools & Materials Needed
- Heat gun or propane torch
- Hydraulic press (or access to a machine shop)
- 600-grit sandpaper / emery cloth / Scotch-Brite
- Freezer and oven for bearing installation
- Standard tools and sockets (including 7mm hex)
1. Disassembly
- Remove the rear brake caliper, rear wheel, and ABS sensor. 🔧 Note the stainless steel spacers on the ABS sensor—they’re critical for proper clearance.
- Remove the “funny fender extension” from the rear drive.
- Separate the rear drive case halves by removing the 8 x 7mm hex bolts. The inner case is the half closest to the wheel; the outer case is attached to the Paralever.
- Extract the crown gear and bearing assembly from the inner case.
- Heat the case with a heat gun or torch (carefully—don’t burn the paint).
- Tap gently on the wheel side of the gear to push it out.
2. Removing the Damaged Bearing
- Remove the old bearing from the crown gear.
- Best done with a hydraulic press and custom bracket.
- Heat the bearing and keep the crown gear cool (cold rag helps).
- Alternatively, lever it off with a screwdriver (carefully!).
- If unsure, take it to a machine shop—10-minute job.
3. Preparing and Installing New Parts
- Clean up the mating surfaces on the inner case and crown gear.
- Use 600-grit sandpaper, Scotch-Brite, or emery cloth.
- Install the new big bearing.
- Freeze the crown gear and heat the bearing (180°F / 82°C).
- If cleaned properly, the bearing should drop into place with no force.
- Reinstall the crown gear and bearing into the inner case.
- Don’t forget the preload shim(s).
- Again, freeze the gear and heat the case.
- The assembly should drop in without force.
- Replace the large oil seal.
- Install it flush with the outer lip of the case.
- Lubricate the seal surface with gear oil.
- Reassemble the rear drive case halves with the 8 x 7mm bolts.
- Replace the large o-ring seal between the cases.
- Reinstall the fender extension, brake caliper, and ABS sensor.
- Don’t forget the ABS sensor spacers!
Parts Required
| Part | Description | Part Number |
|---|---|---|
| Big Bearing | (Updated 17-ball version) | 33121468899 |
| Large Oil Seal | 33127663482 | |
| Large O-Ring | (Case halves) | 33111241257 |
📦 These are the only parts needed for a standard bearing replacement. If your crown or pinion gears are damaged, additional parts and steps will be required.
A Final Word of Advice
Change your rear drive oil at every engine oil change. It’s the best preventive maintenance you can do, and it just might save your final drive from catastrophic failure—like it did for me.
Some dealers (especially in Canada) may not be aware of the updated bearing part number. If your local shop can’t find it, try Chicago BMW or San Jose BMW—both have stocked it in the past.
Stay safe, and ride on.
— Ron Wiebe, BC, Canada
Caveat:
This guide is compiled from a combination of third-party sources, including forum posts, community contributions, and rider experiences. It is intended for informational purposes only and may not reflect official procedures or specifications from BMW. While care has been taken to present accurate and practical information, you follow these steps at your own risk. Mechanical procedures may vary by model and year, and errors in disassembly or reassembly can lead to damage or injury. Always consult a qualified technician or an official BMW service manual if you are uncertain or inexperienced. Additionally, always verify part numbers and compatibility with your specific motorcycle before ordering or installing any components.
