Rear brake advice

[Bob_Roller]

You can reuse a crush washer, as long as it does not have any damage on the sealing areas .
It's usually best to replace them .
When you order some, get them for all locations, a couple of sets will last you a while .

[Tony Smith]

Others will tell you that is safe to reuse a crush washer providing the sealing surface is not marked - they are correct.

I suggest haunting eBay and buying a jumbo sized box of copper washers in assorted sizes, cost is minimal  and you will cover most of the common sizes.

[Barry]

I've used the same crusher washers for 12 years and it wouldn't surprise me if some of them are the original 40 year old ones as the bike came to me  having only done 6000 miles. It's not the cost of new ones that stops me replacing them, more the hassle of buying them.  They never leak,  the thing with solid copper crush washers is not to crush them too much.  The nice thing about my bike when I bought it was it had been maintained with a light touch. Nothing was remotely over tightened which was telling of the PO.

[skippyc]

I call a crush washer, one that is made from copper rolled around a softer core. Then there is flat copper washers which I anneal before reusing.

[Bob_Roller]

I was first exposed to crush washers early on in my aviation career .
They were as you described, a thin copper shell, filled with some sort of fiberous material, I hope it wasn't asbestos .
The solid washers today, are seals as far as I'm concerned .

[peteremc]

Finally got around to getting the job done! Fortunately, there was no oil in the brake side.

Easy fix in the end. The O rings were available and ridiculously inexpensive. I cleaned up the cam and used lots of metho/denatured alcohol as Tony advised - still seemed weird.

Anyway, just thought I would pass on that I started to replace the oil before replacing the cam so that I could keep a torch handy and see exactly how much oil it would take to fill the drive to just below the cam height. It took about 310 mls. Apologies to those not using the metric system, but the recommended fill is 350mls from information in the Haynes Manual.

Cheers

[Tony Smith]

I cleaned up the cam and used lots of metho/denatured alcohol as Tony advised - still seemed weird.

And I'll bet you were nearly as surprised as I was the first time I tried it at how well it works.

but the recommended fill is 350mls from information in the Haynes Manual.

Haynes - distributing information of doubtful accuracy for near on 50 years.

I went looking for the list of BMW revised oil quantities but could not find it. I will keep looking and post here providing someone doesn't beat me to it.

[peteremc]

Also checked the Clymer manual which also says 350 cc (which is the same as mls) but also gives the imperial measurement of 11.8 oz. Working on percentage basis 10 oz. would equal 310 mls.

[Tony Smith]

I can't find it, which is a bit irritating.

But here is what I remember/know. There are two different final drive castings used on pre and post 1980/1981 bikes, the early one (same as /7) takes significantly less oil than the later one.

The earlier one you are supposed to fill to the bottom of the filler plug thread - this guarantees a leak.

The later one you remove the fill check bolt and then remove the vent and fill till oil dribbles out the oil check hole - this also pretty much guarantees a leak.

Some but not all of the later castings have a tube driven into the casting the full width - these, and others that have been so modified, are the lowest leak risk. Those that do not have the fill width tube may have two, four or even more O-rings fitted as BMW and owners tried to stop leaks

In any case in either casting you will dramatically reduce the tendency to leak if your oil level is below the level of the brake shaft. How much below is a matter of conjecture but if you think about it, the thing is splash lubricated by the crown wheel and I suspect that providing the bottom of the crown wheel is in oil that will be enough - when the big seal failed on mine a long way from home and covered the RHS of the tyre with oil I drained it and then refilled so that there was only the bottom 1/2 inch  of the crown gear was covered in oil.  Not only did on;y the smallest amount leak out after that, it ran a couple of hundred kilometres with no problem (and for the first 100km I was stopping regularly to check both leaks and temperature.

So, I think the level can be a lot lower than that originally specified with no danger at all. Now, I know that BMW changed the recommended level, I will keep looking for it.

[Tony Smith]

Ok, searching this very forum I found the "factory" figures of 250ml and 350ml for the early and late model respectively, AND, a general consensus that 20~30ml less in both greatly reduced leaks. Providing the bottom of the crown gear is still immersed I say 50 less would do no harm.