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Last night I received a call from a fellow Airhead traveling cross country on a 77 R100/7 asking for help with an oil leak from his rear drive. He said that he had over filled his drive and now has oil constantly leaking out of the shaft for the rear brakes even when the oil level is correct.

The rider is currently in Montana, planning to ride to northern Minnesota then south to the Minneapolis area, he ask if I could help him repair the leak, having broke down many times on the road and being a fellow Airhead I have to help him out the best I can.
Having it be a long time since I worked on early /7 my question is: If I remember correctly there are two O-rings that seal the brake shaft from the interior of the drive. The Max BMW parts list is not very clear on how the shaft is sealed, or what part numbers are needed for the O-rings. Am I correct believing that we just need to pull the brake shaft and replace O-rings, then refill the drive to the proper amount of oil and everything should be Okay?

It sounds like his rear brake shoes are oil soaked and no longer working, a couple of cans of brake cleaner and a good sanding should remove enough oil to where the brake mostly work.

The rider has a long ways to ride from Montana to Minnetonka Minnesota, I wish him luck and hope he is careful.

It could also be leaking from the crown gear seals.
The crown gear must be removed from the housing to replace the inboard one.
Not a big deal if you have the seals in stock.

I have been in contact with the brother of the /7 owner. I might not make it to MN as he is now stranded in Minot ND with a poor running engine. I think it might be a point gap problem and am trying to talk him through the repairs.

Anyone know anybody that lives near Minot? We sure could use some help.

I after talking to the brother I beleive that his drive leak if from the large seal.

Hi Curt. I'm just looking at my FD (it's in bits on the kitchen table). On mine (74 90/6) there is only a felt ring and a washer on the inboard end of the brake actuating shaft; no o-rings. I guess that felt ring is there to discourage any grease from the shaft going into the brake drum.

If oil is flooding out of the brake shaft it have to be from the big circular gasket. If oil is all over the splines it will be coming from the oil seals - if flooding out of the centre of the spline cup it will be from the inner seal, and if it is flooding over the outside of the splines, it will be from the outer oil seal. I believe the /7 should have the same setup, but I don't have any experience there. In any case, the FD would have to come out and apart. Bad news for the poor sod out on the road but it is not a major job, apart from getting that fekkin' circular gasket cleaned off (took me a couple of hours)

Re the points problem, my guess would be either that the points need filing or that they have closed up due to the fibre cam follower wearing down (no lube on the oiler felt). I guess if he gets the engine working ok he can continue riding without his rear brake, being careful to keep sufficient oil in the FD. Not ideal, but if he keeps a decent safety margin, he might make it home. Do wish him 'good luck' from me if you get the chance.

The oil level in the FD only needs to touch the ring gear and all will be OK for the trip home.

I have family in the Minot area, but none know mechanics etc. In fact I am not even sure who is still alive there. I lived 50 miles away in WWII and owned property there once.

I have an '82 R65 with that same stupid setup. There are three tiny, metric O-rings that leak at their pleasure - why did BMW .....? I also have an R75/6 - completely different rear end/brake shaft set-up.

the oil reservoir of the rear end is open to the brake actuator shaft. The O-rings are supposed to seal it and the oil makes the shaft loose and smooth for braking applications. In reality it is a PITA. Lower the level of oil in the rear end and it will mitigate the prob until you can replace the O-rings.

He should be able to arrive home safely and with a still functioning brake.

Teo