Final drive seals

[Luca]

Bike in question:  82 R65LS

I've got oil pouring from the rear wheel. I've pulled it apart and it seems like the leak is at the brake cam, which seems to be a common problem with these machines. Should I go ahead and get the BMW o-rings or should any properly sized o-ring work?  I've got a little box of metric o-rings...  But it's penny wise pound foolish to try and save some time and money on little bits of rubber if they're gonna fail and wreck another set of brake shoes.

Also, I know I have oil migrating from the driveshaft tube to the final drive. It isn't awful, but should be corrected eventually. However, from what I've gathered, replacing the input seal (or even just taking it apart to goop up the threads etc. is a bit of a job that requires special tools. Is this the case?  If so I can live with the oil migration for a while yet, as money is a bit tight at the moment.

Thanks in advance,
Luca

[montmil]

Buy the BMW OEM O-rings.

I have two large selections of metric O-rings and there's not one that is the exact size required. You can try some but it's a PITA to have to disassemble and refit a couple times before the little light bulb goes on. [smiley=idea2.gif]

Use caution when installing the new rings as there is a sharp edge at the brake camshaft that can easily cut that new O-ring, Order a couple extra and lube 'em liberally prior to reinstall. That's been my personal experience with this deal.

Spend some quality BMW-love time cleaning gear oil out of the brake drum. If the brake shoe linings are contaminated, I have heard that some frugal Airhead riders boil the shoes and skim off the oil by using an ice cube wrapped in a shop towel.  

[Bob_Roller]

I replaced the o-rings on the brake shaft on my '81 R65 in June of last year, I noticed last weekend, that I had gear oil on the rear wheel again .

I lubed the o-rings and the holes in the final drive housing before reassembly, obviously they were damaged during reassembly .

The tool required to remove the nut, is around $35-40 .

The BMW shop manual makes a point to make sure you use thread sealant on the threads before reassembly, or oil migration will occur .

[Luca]

Thanks for the advice, Monte.  I'll go ahead with the BMW o-rings

The shoes are almost definitely original and are very well saturated, so I'm just gonna get a new set.  I've got a little over $100 in gift certificates for my local shop, so I'll just get the parts through them (the new helmet will have to wait).  I'm gonna need a few parts to finish my little fix-up-and-sell Nighthawk 650 project anyways...  got say, working on that Honda has only strengthened my love for the Beemer  [smiley=bmw_smiley.gif]

Anybody have experience with the pinion seal?

[Luca]

Hey Bob,

I have a factory manual for our bikes... but the pinion seal replacement is only covered under the procedure for stripping the entire final drive.  Will I need to separate the whole thing as covered in the manual, or can I replace the pinion seal just by removing the nut on the input shaft?

Thanks,
Luca

[Bob_Roller]

I think the final drive has to come completely apart .

My '82 LS, had the fill port for the driveshaft was stipped out .

I removed the cover and crown gear, then took it to an independent BMW shop, to have the threads repaired .

The best I can tell, is that you can't remove the input seal with the pinion gear still in the final drive .

[Luca]

Alright, I'll get to the pinion seal later.

Thanks for the input.

[montmil]

Luca, What evidence leads you to suspect a failed pinion seal?

[Luca]

I believe I've had some oil migration from the driveshaft tube to the final drive.  I didn't measure what I drained out of the driveshaft tube, but the final drive has been slightly overfilled the last few times I removed the small plug on the back of the unit...  well except for this last time, since the brake cam sits lower than the fill level plug.

I've read that often the seals are fine and the goop job is poor...  but if I do eventually get in there I think I'd just replace everything and not risk having to do the job twice.

[montmil]

Snowbum has a treatise on the issue of over-filled driveshaft lube migrating into the final drive. His suggestion, and that of others, is to drain the driveshaft and refill with 100cc of gear lube. No mas.

That's pretty good advice considering the difficulty in actually "checking" lube level within the driveshaft. Easier and faster to drain n' refill that overfill.

I had replaced the O-rings on the rear brake cam shaft. Then read about the overfill issue. New O-rings aren't leaking and the '81s driveshaft lube is da'Bums advised quantity.

Perhaps try the 100cc of gear lube before spending unnecessary cash.

[steven m]

Good idea.  Replace all the seals while it's out.  I have a migration issue from the drive shaft to the final drive on my bike, but it is very slow, for now, so I haven't taken it apart.  If your splines aren't in good shape you might consider picking up a used unit with good splines, rebuilding that, and then just swapping it out.  Or drop it off with an expert have have it rebuilt.  Considering the massive torque out bikes make, ha ha, unless the PO was drag racing, once again, ha ha ha, yours should be in good shape. I changed the transmission, drive shaft, and final drive oil at the same time to factory specs.  I'll drain them all at the same time into a graduated beaker and find out exactly where the oil is moving to/from.

[Luca]

The PO never even wore out the factory tires, let alone beat on it. All my splines are fine...  I think the issue was just one of aged rubber that didnt get much use over the last 30 years.

Ive read Snowbums encyclopedia and have been aware of his (and D. Ausherman's) notes on migrating oil since before i put the bike on the road. Since the d-tube oil level isnt extremely critical and im short on cash (and gonna sell my car and look for a truck) I'll deal with the pinion seal at the end of the season and the migrating oil until then. Ive also got a semi-synthetic in there that might find leaks more easily than a conventional gear oil

[montmil]

... Ive also got a semi-synthetic in there that might find leaks more easily than a conventional gear oil

Seems the BMW OEM, never-been-changed seals don't always like the synthetic oils. Numerous reports of leaking engine seals after switching to syn. Returning to dino oils and the leaks... don't.