master brake cyl.

[enginerod]

I have a leaky master brake cyl. on a 75 R90/6. My question is can it be taken apart and rebuilt? I can see a snap ring holding the piston in. Is there a o-ring on the piston? This is where the leak is coming from. Are there any rules I need to follow?

[Isamemon]

well of course it can be rebuilt
the kits run about $66
and if it is leaking, you really want to fix it asap
The old BMW brakes are not the best in the world, esp compared to newer bikes, adn anything that hurts the workings is not a good thing at all

well, let me change that, in most cases they can be rebuilt, if it is not scored or pitted internally

[20774]

You'll want to try and clean up the bore if pitted or rusted, otherwise it will just cut the o-ring again. You can find an appropriate sized wooden dowel and wrap some sandpaper around it. There are companies that can resleeve the older master cylinders. The other option is to retrofit a handlebar master cylinder... There's been quite a bit of discussion about which models will work. There's issues with master cylinder bore diameter and getting the right one plus routing the new hose.

[enginerod]

Thanks for the information. I have a large selection of O-rings. Can I just replace the o-rings inside? Is there more to a rebuild kit than o-rings?

[20774]

It's been a while since I've seen one of these kits. I suppose you could use any o-ring as long as it was the correct dimensions (??) and was OK for use in DOT3/4 fluids.

[Bill Burke]

James Klossner has prepared an excellent report on the procedure.

http://tinyurl.com/6rleo4

On page 4, the "cup" installation is particularly tricky. Warm the new rubber up in warm water to try to get the install done without tearing the rubber.

[enginerod]

Thanks Bill............I am going to order a rebuild kit on monday. The photos are great. How hard is it to take off the last rubber cup that is still on the shaft? I don't think I will have very much trouble after seeing the steps.

Thanks again Rodney

[Bill Burke]

Thanks Bill............I am going to order a rebuild kit on monday. The photos are great. How hard is it to take off the last rubber cup that is still on the shaft? I don't think I will have very much trouble after seeing the steps.

Thanks again Rodney
I don't know Rodney. Jim Klossner rebuilt mine. But dental pics work well for this sort of thing. I'd try to get the old one off intact if I could, just to have an emergency second shot at it if I tore the new cup trying to put it on. Best of luck and let us know how it goes.