Rear transmision seal

[EddyQ]

Went to the dealer today and got a new wheel hub, fuel pump and fuel strip all covered under warrentee. However, they said my tranny rear seal is leaking and needs to be replaced. I took a look and there was not much for oil. None anywhere except a very small amount on what looks like a rubber seal between the swingarm and tranny. They said the oil typically runs down the swingarm and comes out near the final drive. But nothing was coming out yet. SO, I didn't get it replaced.

 

Is this a difficult job requiring special tools?? They said the swingarm needs to come off for access. Seems like an opportunity to get in there and lube up the front spline and possibly inspect other things. Any opinions?

 

Oh, the bike just rolled over 40Kmi.

[dirtrider]

Morning Eddy

 

Nothing really exotic in the tool department but you will need to remove the swing arm.

 

If it isn't leaking a lot of gear oil then probably not worth doing yet.

 

You might look in the final drive end rubber gator boot to see how much oil is in there.

 

The bad (expensive) news is-- you might also find your drive shaft U joints starting to go once you get in there.

 

 

[EddyQ]

Thanks DR!

If it isn't leaking a lot of gear oil then probably not worth doing yet.

You might look in the final drive end rubber gator boot to see how much oil is in there.

That's my thoughts as well. I plan to do the FD fluid before it snows and I'll get a decent view of the issue then.

 

The bad (expensive) news is-- you might also find your drive shaft U joints starting to go once you get in there.

So, is this something that goes at 40Kmi? I assume to check, I would look for excessive play in the joint.

[dirtrider]

 

The bad (expensive) news is-- you might also find your drive shaft U joints starting to go once you get in there.

So, is this something that goes at 40Kmi? I assume to check, I would look for excessive play in the joint.

 

Morning Eddy

 

Or excessive tightness (make sure the U joints articulate smoothly without binding or notchy feel to them)

 

Obviously loose is bad but so is binding or notchy.

[lkraus]

BMW specifies a special tool to re-install and torque the swing arm bolts.

 

You can make a substitute pretty simply:

 

It might also be possible to do without the special tool, I've not needed to attempt this job yet. I'd think with the rear strut off, you could simply feel for looseness or binding after locking the bolt in place, though it might take a few tries.

[dirtrider]

Morning Larry

 

I milled a 30mm socket with a large window as it does make multi-jobs easier but for a one-off deal you really don't need anything special. (don't even need a deep socket)

 

Once you properly adjust the inner stud just mark (index) the stud's position (a paint mark at the very top will work).

 

Then back it off slightly & torque the outer nut, then check the index mark. If it (the stud) moved into the correct clocking as the nut torqued up then you are good to go. If it is short or long of position then loosen the lock nut & back the stud up more (or clock forward) & re-torque the outer nut. (usually a try or two will have the stud index mark rotate into the correct location as the nut torques up)

[EddyQ]

Thanks for that Larry and DR! If that is the difficult part, I think I would be fine.

[dirtrider]

If that is the difficult part, I think I would be fine.

 

Afternoon Eddy

 

Yes, there is nothing real difficult or requiring unique special tools--It's just a big pain in the a$$ to replace that seal.

 

You might be able to stop or slow the seep just by changing to a different brand/type of transmission gear oil. Some gear oils (like Mobil-1) have very little seal conditioner in them so do leak easier than some of the more conventional gear oils.

[Don_Eilenberger]

One other thought.. what can be perceived as a rear-transmission seal leak might not be. Does the oil smell like transmission oil?

 

If not - has the engine oil been overfilled? The vent for the engine goes into the airbox. If the oil is overfilled - the oil vapors created condense in the bottom of the airbox (which is formed with valleys and lumps in it to fit to the top of the transmission.) Somewhere there is a drain in it - which will dribble the oil out on the top of the transmission, where it runs down around the starboard (right side) top and ends up where the rubber gaiter fastens to the transmission.

 

It will then flow down the gaiter and drip off the bottom. If there is enough of it - it will flow back along the swingarm.

 

BTDT - dealer diagnosed a rear seal leak on the tranny. I didn't think so, so I started looking very carefully, and found a barely visible trace of oil above and in front of the gaiter.

 

That inspired me to remove the air filter, and using a video-protoscope sort of mechanics tool, look into the airbox, where I found oil condensed in the valleys on the bottom of the airbox.

 

About 20 minutes with rags and towels on a long screwdriver pushed into the airbox through the filter hole mopped most of it up.

 

No more leak. The leak was gone. No longer there. Fini.

 

Worth checking, especially if the oil doesn't smell like transmission fluid.

[EddyQ]

Thanks Don. I will check that as well. I did top off the oil a week before going to the dealer. If I overfilled, it wasn't by much. I think the level was just visible at the very top of the sight glass.

[Don_Eilenberger]

Eddy - the other BIG clue that made me start looking for an alternative leak source from the dealer diagnosis, was there was oil on the front of the rubber gaiter type boot.

 

Since that end of the boot is held onto the transmission quite tightly with a tie-wrap, it would seem doubtful that a leak on the output seal would result in oil there.

 

Dealer mechanics sometimes tend to assume the worst case scenario, and miss the simple stuff.