Leaky rear end

[Dave Backmarker]

On my R90S that is. Performing normal maintenance, I filled the drive shaft per spec and after a very brief ride, I discovered gear fluid coming out the vent and when I opened the filler hole, the final drive was indeed over full. I pulled the final drive unit and heard a clunk on the floor as I lifted the final drive away from the drive shaft. The collar nut was floating around. I have a new seal and a nifty tool to tighten the nut to the correct torque.



Has anyone had an experience like this? I have a hunch this was caused by the previous owner not tightening the nut properly. Are there any recommendations for what type of gasket material to use along with the paper gasket between the final drive and the drive shaft? I'm thinking a little gray Permatex.

DaveM
1975 R90S
2000 R1100RT

[SteveD]

Will that have any effect on the life of the pinion bearing #9?
If so, then I'd replace it whilst apart. There's a tool to remove the threaded ring #6 and the important thing is a surgical cleanliness in there before reassembly.

Ideally you won't need to go back in there if done correctly. The shaft:fd gasket doesn't need much, if anything. I've replaced a few over time when swapping out fd's and I put them in dry, with the four nuts torqued to spec only. Surfaces are as clean as possible first.

[Duane Ausherman]

Yep, somebody screwed up in the past. I would use a gasket, as it originally had.

The main error that occurs with this job is installing and tightening up the 4 nuts before insalling the axle. Put the 4 nuts on by finger, but not even slightly tight. Then install the axle to align the final drive, then tighten the 4 nuts up.

I would probably do as you plan, but be aware that you still could have oil transfer when finished, so test it out before going on a long ride.

[Dave Backmarker]

SteveD and Duane,
Thank you for the responses. I have the two tools from Cycleworks.net to hold the pinion as well as remove the slotted ring. I've replaced the seal and carefully reassembled the final drive and installed the final drive to the drive shaft with the benefit of your posts. Thank you! With my son's help, we cleaned everything to a surgical level of cleanliness.

I'll be sure to fill the drive shaft and final drive and test with a few very short rides to determine if the gear oil from the drive shaft is leaking into the final drive before I take the bike on a longer ride. I'll probably wait for a warmer day as I'm in the middle of New York state.

DaveM
1975 R90S
2000 R1100RT

[Duane Ausherman]

Put in a measured 100cc of oil in the swing arm and the final drive to the bottom of the threads. This way you know that you have a "standard" from which to measure after a few hundred miles.

If the final drive is installed while aligned, then the axle should go in and come out very easily. There is enough "play" in the final drive mounting that one can misalign it so badly that the axle must be pounded in and out. Sometimes they have been that way for years. Sometimes BMw dealers did that to customer's bikes.

I suggest doing the "shake the wheel test" before riding it, just to make sure that nothing got screwed up with the axle/wheel bearings.

[Deleted User 62]

Quick question: should the rear drive oil level be checked while it's on the center stand or sidestand, or does it even matter?

[Dave Backmarker]

Duane,
I added 150 cc in the drive shaft and then 250 cc in the final drive per my Haynes manual. The 250 cc brought the level just below the threads when on the center stand. 100 cc?

I will try the shake test. I ran the transmission through the gears (I'd just rebuilt the transmission) and everything appears to be turning smoothly.

DaveM
1975 R90S
2000 R1100Rt

[Duane Ausherman]

Quick question: should the rear drive oil level be checked while it's on the center stand or sidestand, or does it even matter?

There is no such check of oil level on the swing arm, never was and never will be. Anyone suggesting a "level" is just showing ignorance.

If ( big if you put the correct amount in when you filled it, then the check for the swing arm oil is in done in 3 ways.
1. Take a look around the swing arm and final drive for evidence of an oil leak.
2. To check both final drive and swing arm at once is easy, just remove the filler plug for the final drive and if the level is still correct, then both are correct.
3. Drain the swing arm oil into a measured beaker and record the amount. You should get out exactly what you put in.

There is one place for an error. When a transmission has just been rebuilt, the building could have installed the rear cover seal backwards. That will allow the oil from the swing arm into the transmission. That level will be too high and it can only come from the swing arm. Engine oil can't get into the transmission.

OK, use 150 cc as specified for some models. Never put too much oil into the swing arm. The higher pressure will force it into the final drive, even when it has been sealed up properly. It is far better to run the swing arm low than high. They will work just fine with only 50 cc in them.

[macdaddy]

A new or clean DS boot will hold some oil also, 20ish cc

[Deleted User 62]

Sorry Duane, I meant the oil level in the rear drive, not the swingarm. I know the spec is to the bottom of the threads, but that level would change if the bike were on the centerstand, with the rear drive hanging, or on the sidestand with the suspension under load. I suspect it wouldn't make that much of a difference, but I'm curious as to the "factory" method.