I first noticed the problem while pushing the bike out of the garage. The rear tire made a strange squishing noise. I figured perhaps it was low on air, or maybe the tire compound was different (this was a fairly new tire after all) After checking the air pressure, I placed the bike on its center stand and spun the wheel. All seemed fine. However, once I tried rocking the wheel back and forth by holding it at 3 and 9 o’clock, there was noticeable play. The wheel rocked on its axle roughly a millimeter or so.
“Ach du lieber, mine final drive ist kaputt!”
How could this happen? I changed the final drive fluid religiously. The bike has only 53,000 miles. So I contacted my BMW dealer in Orange to get their opinion, and was quoted $3000 to fix. WTF???? Absolutely horrified, it was obviously time for plan B.
First step was to check the bike’s shop manual to see what it had to say. There seemed to be a lot of custom tools required. Not good. So I contacted my friend who works at a machine shop to see how hard it would be to replicate some them. No problem, anything to see what makes this bike tick.
Than it was off to the liquor barn for a case of liquid courage, and I got started.
FINAL DRIVE REMOVAL
Removing the final drive is a fairly straight forward process. With the rear wheel off, I place some blocks under the catalytic converter to act as support in case some one accidentally leans on the bike. I also tied the center stand to the sump guard to prevent any chance of the bike moving forward.
I figured Id try to do as much disassembly as I could while the final drive was still attached. I started with trying to remove the circlip that holds the wheel flange in place. This proved to be impossible without a circlip removal tool so I was off to Harbor Freight where I found the perfect tool and a cheap laser powered heat thermometer (something that would be really useful later).
With the proper tool in hand it was time to remove the circlip, but to my dismay the prongs were too large to fit in the circlip holes. You got to be kidding me? So I bust out the metal file and start modifying. Soon I had it at the right diameter and the clip came off without a fuss.
Next I removed the brake disc. Before doing that, I decided to mark on the wheel flange where the disc was attached. Not sure if this matters, but what the hell. At the very bottom of the final drive, there is a relief where you can get access to the bolts holding the disc in place.
I removed the cover to the bottom mount with a small screw driver.
There was also a circlip here that had to be removed.
There is a lot of information on advrider on how to un hinge the final drive and drain its fluid so no need to get in to any of that. I captured the fluid in a cup to check for any metal filings or anything that might tell me what’s going on inside.
Seemed pretty clean to me.
Once drained, it was time to remove the assembly. The shop manual says you should use a retaining strap to secure the FD so it wont drop. No pic, but the strap goes through the axle shaft hole and than attaches to the bike frame above. It didn’t seem that necessary to me. Once the bolt was almost all the way out, I could hold the assembly with one hand and drive out the bearing stud using a drift.
Next I removed the shaft seal cover using a screw driver.
And than the shaft seal circlip using a little hook.
At this point, I did NOT remove the shaft seal itself. I recalled speaking with one of the mechanics at the Phoenix BMW dealership about this seal, and how it needed to be placed at a specific depth. They had a special tool for this. Without access to this tool, one would need to be made.
After a little bit of cleanup, I headed off with final drive in hand to my friend’s machine shop.
FINAL DRIVE DISASSEMBLY
Step one was to get the wheel flange off. This requires a puller system. After making a few measurements, we started with milling the disc that would press against the axle.
The finished product:
Next the fixture to attach to the wheel flange.
The finished product:
Before attaching the fixture to the wheel flange using the wheel bolts, be sure to mark the position of the wheel flange on the axle for assembly later.
With fixture attached, heat up the wheel flange to ~100..110 degrees Celsius using a heat gun. My new Harbor Freight laser thermometer worked like a champ here.
Once heated up, the wheel flange came off easily.
Next it was time to remove the housing cover. We marked the shims so they could be replaced exactly the same way during assembly.
We removed the screws holding the housing cover. The shop manual says to heat the housing cover to ~80 degrees Celsius, but that didn’t seem necessary. We placed the disc created previously on the opposite side to the axle, and used it to help push the assembly apart.
Next step was to remove the wheel axle from the housing cover. This required another fixture to hold the housing cover securely in place.
The axle disc made earlier was used again to push the parts apart.
Came apart nice and easy.
Once apart we could start seeing the problem. Lots of greasy rust all around the main bearing.
Next step was to remove the shaft seals. We started with removing the larger main seal with a screw driver.
More greasy rust. So it would seem that the main wheel bearing probably went bad.
Than we removed the smaller shaft seal on the main cover housing also using a screw driver, but not before measuring its depth for later. During assembly we want to place the new seal at the same depth as the old one.
Than it was on to finally removing the bearings. We started with the smaller crown wheel needle bearing. A simple disc pusher would not work here because of how the bearing is seated.
You can see how the needle bearing is seated. A disc can not make full contact with all of the bearing. This required something more rectangular.
We had to modify our fixture to handle the shape of the main housing cover by trimming away some of it. Once that was complete, we could attach the main housing cover flush up against it.
With the rectangular disc in place ready to push the needle bearing out.
Again you should heat up the housing to a release temperature of ~100 degrees Celsius.
The main bearing had another circlip that needed to be removed first.
Than it was on to make another disc just shy of the diameter of the bearing so we could press it out.
Once again we placed, the housing cover in our fixture and pressed out the bearing. Again heating the housing to a release temp of ~100 degrees Celsius.
Bearings and seals.
The bevel pinion gear showed no wear and moved fine, so we decided not to touch it.
PARTS AND INSPECTION:
First I cleaned all the parts. while being very careful not to let any dirt accidentally get near the bevel pinion. It appeared to be in good shape and I didn’t want to change that.
I had ordered new parts before taking the final drive apart and all looked in order with the exception of one gasket ring. This gasket ring is shown on the final drive assembly diagram, but was missing from mine.
This gasket ring should be placed between the main bearing and wheel flange. However, after making a measurement, there was simply no way you could make it fit. I figure this may have been added to later model final drives. This is unfortunate because with out this gasket ring, the main bearing is exposed. My guess is that water will inevitably penetrate the main bearing seal and destroy it as it did to mine.
The shop manual recommends that the thickness of the shims between the housing cover be checked when a new bearing is installed. The new main bearing was identical to the old one so we figured there really should be no reason to adjust them and left it at that.
The first step was to mill push/puller discs for the bearings and seals.
We started with the crown wheel main bearing and seal. After attaching the housing to our fixture, it was just a matter of heating up the housing to ~100 degrees Celsius and pulling the bearing into place until seated.
After installing the circlip, we pulled the seal into place the same way.
Than it was on to the needle bearing. At first glance the new needle bearing looked like it could be installed flipped any way. However, this is not the case. There is a definite front and back to it. One side of the bearing sleeve is shallower than the other. This allows gear oil to penetrate the bearing easier. This side of the bearing should be installed toward the inside the housing where all the gear oil is for improved lubrication. There is no mention of this in the shop manual, and we almost missed it. Sorry no pic, but is pretty obvious when you look at it.
We swapped housing covers on our fixture and pulled the bearing into place. Again heating the cover before hand.
Next step was to install the wheel axle in to the housing cover. We had to offset the housing cover a bit on our fixture in order to accommodate the axle. Than it was just a matter of pushing the wheel axle until seated. Be sure to lubricate the sealing lip of the shaft sealing ring before hand. The axle should be turned as well during the process in order to keep the sealing lip from doubling over on itself. The axle turned on its own while we wrenched it in to place.
Than it was time to install the housing cover. We replaced the housing cover O-ring and lubed it a bit for easier assembly. We placed the housing cover in position and turned the axle until we felt the gear splines engage. Than we placed the shims in the same position as they were before. Finally we used a press to lightly push the assembly together evenly.
After screwing the housing covers together, I placed the entire final drive assembly in the freezer to prepare it for the wheel flange.
The wheel flange went in to the toaster oven.
We aligned the wheel flange with the axle using the alignment marks drawn on the parts during disassembly.
The shop manual says that after heating the wheel flange to ~110 degrees Celsius it should slip in to position easily in order to prevent damaging the coating on the wheel axle. Ours required a bit of persuasion with a press. Not a lot though.
Once the wheel flange was seated all the way, we installed the circlip. The manual mentions that if you install the circlip the wrong way it could cause the brakes to overheat. Honestly have no clue what they are talking about. The circlip can only be installed one way, and seems identical on both sides. Decided not to worry about it.
Almost done, just one more step, installing the outer seal. We milled a pusher to the exact depth as measured before hand and pressed the seal in.
And with that we were done. All that was left was to attach the final drive back on to the bike, fill with fluid and test.
The play in the rear wheel is now gone, and the wheel turns freely. No more squishy sound either. At this point, it hasn't leaked and appears as good as new. I guess time will tell.
The bearings and seals cost me a couple hundred, I forget exactly how much. I think we used about $20 in aluminum, and went through 2 cases of beer. Of course, the knowledge gained was priceless.
Hope this has some value to some one out there.