Rear brake advice

[peteremc]

Hi all.

My bike (1982 R65LS) has developed a small, but very annoying and most unexpected external oil leak from my rear brake cam. I will take the wheel off this weekend and hope it hasn't leaked inside the brake drum as well. I guess the only thing it can be is the rubber O ring(s) that sit on the cam that are allowing oil past.

My question is this: Do I pull the cam and just go to the local auto parts supplier and try to match the size? This is what I did when I last reassembled the rear brake bits (probably a bit over a year ago) so unfortunately I no longer have the original o-rings. Or should I be ordering a couple of O rings from the BMW parts supplier so that I know they will be the correct size?

Obviously not a big deal either way financially for 2 tiny rubber O rings, but as I just bought the last pair of O rings from a local auto parts place and they appear to be failing, they may not have been the correct thickness and I may be safer going to the BMW parts place.

Any/all advice appreciated.

[Tony Smith]

Sadly if you see oil it is probably on your rear brakes. i say M'eh they never worked a damn anyway, wipe it off and put them back together. If you are feeling like making work for yourself, wash them is degreaser ( I would use brake cleaner but be careful you do not de-bond the shoes)

The "O" rings are catalogue ones and will cost you all of $0.25 each at Allied bearings in Aumuller St - take the brake cam with the defective "O" rings on it for matching purposes.

It is just vaguely possible to damage the O-rings by being brutish with them on assembly. Little known but true fact, the correct assembly lube for rubber O-rings is Metho in copious quantities.

[Barry]

I agree, standard NBR O rings should be fine with oil.

The number of O rings increased in an attempt to cure the leaks. A liitle lower oil level might help and that won't harm the final drive.

[peteremc]

Thanks Tony. In fact Allied Bearings was where I purchased the current ones. The bloke I dealt with didn't want to process the purchase for such a small amount so from memory I made a small donation to the shop beer fund. So if they're a generic item, I'm not sure why they might be leaking.

And I'll have you know that I have a semblance of rear brake by using brake cleaner and a very fine grit sand paper on both surfaces. I was somewhat surprised by the degree of the result and have become used to having a rear brake.

If I was again fitting O rings to contain oil I would be coating them in oil prior to fitting. Wouldn't metho in copious quantities just dry them out or is this what would encourage the seal?

[peteremc]

Thanks Barry. Mine has two O rings - one on the brake side and one on the external side.

And I had wondered about lowering oil level considering the splashing around that must go on in there, but didn't want to tamper with this. I'll fit the new O rings first and see how it goes.

[mrclubike]

I am using quad rings
They have 4 sealing edges instead of 2
They also have good tension when installed

[Tony Smith]

Thanks Tony. In fact Allied Bearings was where I purchased the current ones. The bloke I dealt with didn't want to process the purchase for such a small amount so from memory I made a small donation to the shop beer fund.

Yeah, they are like that, I usually buy some hand cleaner, a bag of shop rags or something else I can use for exactly the same reason.

 So if they're a generic item, I'm not sure why they might be leaking.

I'd hazard a guess (in order) that either your oil level is too high, you used expensive (and un-needed) synthetic oil [it has migratory properties that would make an African Swallow envious] or you accidentally caused some harm on assembly.

And I'll have you know that I have a semblance of rear brake by using brake cleaner and a very fine grit sand paper on both surfaces. I was somewhat surprised by the degree of the result and have become used to having a rear brake.

That works - for a while. The natural state of any airhead drum rear brake is that they are marginal in operation - this is not a bad thing as they actually have pretty decent (for the time) front brakes and the lazy rear brake can be passed off as a safety feature :-). In contrast (early) airhead rear disc brakes tend to be vague in operation and altogether too powerful - I fitted a later and larger diameter rear master cylinder to my R100RS to calm it down a bit because a mere brush of the rear lever would lock the wheel.

If I was again fitting O rings to contain oil I would be coating them in oil prior to fitting. Wouldn't metho in copious quantities just dry them out or is this what would encourage the seal?

I do realise that it is counter intuitive using a "dry" fluid as a lubricant. All i can say is that a long time ago I was told to use Meths and I didn't believe it either - then I tried it and was very surprised indeed. I do suggest that you try it (as the actress said to the Bishop).

On a completely different note, a very old friend is visiting me this weekend (and is bringing goodies to assist the RS resto project) He is borrowing Sylvia's R65/80 and we are going up to Yungaburra for breakfast if you are interested [no pressure, you have all day today and all of tomorrow to fix your brakes]. This means I will be missing the memorial ride for the Cattanas but I actually think they would understand and approve.

[Bob_Roller]

OK,  what is metho ??
The first time I replaced the o-rings on the brake camshaft I cut one .
I put a slight bevel on the opening hole on the brake shoe side of the final drive, so the o-ring doesn't come up against the edge of the final drive cover .
It starts to compress it and so far I have not pinched one since .

[mrclubike]

this is a Quad ring
way better than a standard O ring

https://daemar.com/quad-rings-30.html/

[Tony Smith]

this is a Quad ring
way better than a standard O ring

https://daemar.com/quad-rings-30.html/

Gunna get me some of them!

[Tony Smith]

OK,  what is metho ??
 .

Technically it is "methylated alcohol" aka "methylated spirits," "Meths" and "Metho"

It is alcohol (usually sourced from wood alcohol, but may also be from sugar cane so it may be any blend of Methanol and Ethanol)  for general use that has been made unpalatable for drinking by the addition of about 10 per cent methanol and typically also some pyridine and a violet dye.

Pryridine is a colourless volatile liquid with an unpleasant odour, present in coal tar and used chiefly as a solvent.


Meths was/is traditionally made from wood and therefore Methanol but recent changes in the amount of alcohol produced from sugar cane and is therefore ethanol.

Down and out people have always drunk Metho when unable to afford anything else - having tried it once as an experiment I cannot imagine how they keep it down, but there are many "recipes" such as mixing with lemon cordial base, straining through egg white, and even straining after mixing with shoe polish which are alleged to make it easier to drink.

Even if you can get past the fact that Methanol will make you blind, kill your intestinal system and quite possibly kill you outright, the taste (courtesy of the Pryridine) is truly vile and the dye will stain your mouth and lips (which at least makes diagnosis at the ED a bit easier).

[Bob_Roller]

It's called denatured alcohol here .
Additives, like rubber cement solvent, auto fuel, to make it unsuitable for human consumption .

[BPT]

If I'm looking correctly at the fiche, those 2x10mm rings in MrClubike's pic are the correct size for the brake cam?

[Bob_Roller]

Yes, that's correct size .

[peteremc]

Thanks all. As it turned out, I didn't get anywhere near the bike on what turned out to be a very full weekend. Having a fairly large block of land with many tropical plants following plenty of rain and being right in the middle of growing season in the tropics, some garden maintenance was required, by order of "she who must be obeyed". That's OK. everyone's happy.

So, I missed your kind invitation for breakfast in Yungaburra Tony. And it would've been spectacular morning for a ride up the Gillies on Sunday morning. I snuck out for a run up to the Rex Lookout and a sneaky beer at Ellis Beach late yesterday afternoon (on another bike, obviously).

Back to the job I need to do. Before I pull the brake cam, I'm going to have to drain the final drive oil. Does anyone happen to know how much oil I can put back in to keep the level below the cam?

One more question I've been meaning to ask a million times: As this is an unscheduled activity, I don't have a replacement crush washer for the drain plug and it will take me some time to get one, so does anyone re-use crush washers and if I did on this occasion, what are the chances of it not doing it's job properly?

Cheers