GS Rear Brake - Oil Contamination?

[R100RT Mark]

Got to ride a friends “new” 1991 GS this week and found it to be a lot of fun but the rear brake stinks. I am used to less than stellar performance from the (same?) rear brake of my 1993 R100R, but this was much worse. He pulled the wheel today and says it looks like there's some oil on the shoes, but no sign of any oil leaking in from anywhere. I’ll get a look at it this weekend, but wondered if anyone has any idea of how oil might have got on the shoes?

[R100RT Mark]

OK, took a look at the issue here. Shoes definitely seem to have some oil or grease contamination but there is no sign/evidence of where any oil or grease may have come from. Any thoughts?

[boxermoose]

Originally Posted by R100RT Mark

OK, took a look at the issue here. Shoes definitely seem to have some oil or grease contamination but there is no sign/evidence of where any oil or grease may have come from. Any thoughts?

IIRC there are a couple o rings where the brake shaft goes thru the final drive housing - I'd kinda assume some gear oil (or mist) has migrated across the shaft and settled out on the inside of the drum. Mixed with brake dust it's look like paste

[hardwaregrrl]

Originally Posted by boxermoose

IIRC there are a couple o rings where the brake shaft goes thru the final drive housing - I'd kinda assume some gear oil (or mist) has migrated across the shaft and settled out on the inside of the drum. Mixed with brake dust it's look like paste

+1 make sure to get the correct sized O rings for the brake cam. no substitutions. Get them from BMW.

[R100RT Mark]

Originally Posted by boxermoose

IIRC there are a couple o rings where the brake shaft goes thru the final drive housing - I'd kinda assume some gear oil (or mist) has migrated across the shaft and settled out on the inside of the drum. Mixed with brake dust it's look like paste

Originally Posted by hardwaregrrl

+1 make sure to get the correct sized O rings for the brake cam. no substitutions. Get them from BMW.

OK, are we are talking about item #20 [part #35 21 1 457 605] GASKET RING - 12X1 on this diagram? There's only 1# called off. What is the function of the gasket ring #18 and might this be a source of "misting"?

[R100RT Mark]

Bumping this to see if I can get guidance here on the o-ring/gasket ring that folks advise might be an issue for the GS rear brake shoes being discussed. I'll get to fiddle with this again this weekend and would like to make some progress.

[Box'a'bits]

Are you absolutely sure its oil & not just old & glazed shoes? They dry out, & then are next to useless. DAMHIK

[Ghilli]

I had the same problem on the monolever g/s final drive. Oil was definitely seeping trough the brake cam shaft and onto the drum surface. Even replacing the o-ring with a BMW o-ring, it still leaked. I then took the shaft and machined a new slot for a second o-ring next to the original one.

Worked perfectly until a week later when the leak migrated to the outside, leaking oil down the brake lever onto the rim..

Maybe it could be the vent valve on the top that is clogged or something, forcing the oil past the o-rings when the temperature and pressure increases.

[R100RT Mark]

All good thoughts. Tech session planned for this weekend. Should get to the bottom of this.

[_cy_]

first thing to do is drain oil... then carefully refill following instructions in factory manual. degrease all suspected areas of leak very carefully. then keep tabs on any new oil showing.

this should reveal exact source of oil.