Topic: My stupid master cylinder rebuild mistake - help!

[j2dawson]

I received my master cylinder kit today and was putting it in. As I was installing the snap ring my hand slipped and everything went flying across the garage. I retrieved everything except the rubber cup that goes over the end of the spring. I've looked for hours and it is nowhere to be found. It appears that it can't be purchased separately. Naturally I have already thrown away the old one.

Does anyone have a used one that they want to part with? I hate to spend another $28 just for that piece of rubber.

Thanks,
Jim

[madmtnmotors]

I'll take a look, I should have a used one bagged up somewhere, unless someone else beats me to it. I know the rubber ring on the piston is the primary pressure seal, but does anybody know if the rubber cup on the end of the spring is a critical seal, or does it just cushion the spring?

[j2dawson]

Thanks for looking Wilbur, I really appreciate it. If you find one let me know how much you need for it and I'll get it right out.

Jim

[madmtnmotors]

Actually, looking at the schematic in the manual, the rubber cup under the spring is labeled "primary cup" and the rubber around the piston is labeled "secondary cup". This makes sense looking at their orientation, so I would say the cup under the spring is the most important one. I would suggest scouring the garage a couple more times to see if you can find the new one you lost. If it were me, I would not want to install a used primary cup, which is all I would have.

Maybe someone has a partial kit laying around? Sorry I couldn't help with a new seal.

[j2dawson]

I would be willing to try a used one if I had one.
Thanks anyway.

[krusty]

We wouldn't be talking about the piston dust seal would we?

[madmtnmotors]

I would be willing to try a used one if I had one.
Thanks anyway.

I'll see what I've got, I know I bagged up the remains of more than one MC rebuild.

[j2dawson]

We wouldn't be talking about the piston dust seal would we?

It's the rubber cup that is between the spring and the piston.
I think the primary cup is the one on the shaft of the piston. This might be called the piston dust seal.

[krusty]

OK its not the dust seal then. If you want brakes you'll need it.

[madmtnmotors]

Found a couple. PM me your address and I'll pick out the best one and stick it in an envelope.

[j2dawson]

Thanks to Wilbur's generosity, I got my master cylinder rebuilt. I also rebuilt the caliper and all is working well.

[BobbyR]

Thanks to Wilbur's generosity, I got my master cylinder rebuilt. I also rebuilt the caliper and all is working well.

Wilbur's used one will get you going for sure and it is nice of him. If you intend to keep using the bike, when I got a few extra bucks I would purchase new parts in the near future.

[madmtnmotors]

Thanks to Wilbur's generosity, I got my master cylinder rebuilt. I also rebuilt the caliper and all is working well.

Wilbur's used one will get you going for sure and it is nice of him. If you intend to keep using the bike, when I got a few extra bucks I would purchase new parts in the near future.

Yep, I made it clear that it was for "testing" purposes!