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Old 01-06-2015, 04:41 PM   #1
OregonBob OP
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Master cylinder repair kit R100

I have a 1983 R100. Mechanics say the master cylinder is leaking. After careful observation, it seems so. It isn't much, but after riding around, I see a little bit of fluid weeping out where the front brake handle is.

Looking at the Max parts fiche, I see there was a master cylinder repair kit for up to 9/80, but nothing for the 1983. It would be great if I could repair this, rather than having to buy "the whole unit" for hundreds of dollars.

What are my options?

thanks. Bob
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Old 01-06-2015, 04:44 PM   #2
Solo Lobo
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If you check the underside of the MS, it should be marked with a size (ex 13mm) and you can buy the correct kit.

Make sure to strip your MS before buying the kit to check for pitting, which would have to be honed out, and would require a larger sized kit.

You might also check motobins in the UK, IIRC the kits ran something like $80 in the US and the motobins complete MS was $130 or something
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Old 01-06-2015, 05:55 PM   #3
op48no1
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Mine was leaking. I bought a new piston, which comes with the rubber seal or ring, IIRC.

I had a hard time getting the old piston out on account of corrosion. I ended up putting it in a vice and twisting and pulling until it was finally free. I figured there was nothing to lose, so I wrapped some fine sandpaper in a tube, stuck it in the cylinder bore, and did a little gentle up-and-down, back-and-forth. Then I reassembled the piston into the cylinder, put it all back together, and it works fine and hasn't leaked since.

YMMV.

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Old 01-06-2015, 09:54 PM   #4
Rob Farmer
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Quote:
Originally Posted by OregonBob View Post
I have a 1983 R100. Mechanics say the master cylinder is leaking. After careful observation, it seems so. It isn't much, but after riding around, I see a little bit of fluid weeping out where the front brake handle is.

Looking at the Max parts fiche, I see there was a master cylinder repair kit for up to 9/80, but nothing for the 1983. It would be great if I could repair this, rather than having to buy "the whole unit" for hundreds of dollars.

What are my options?

thanks. Bob
I wouldn't bother putting a new piston in it unless you are going to have the bore re sleeved. I put a new piston in my GS weeks before a trip, no sign of any leak after that until I was in the back of beyond and it let rip big time cutting several days of the trip and dumping brake fluid down the side of the tank. For what it costs I'd fit a new cylinder and then forget about it for the next 20-30 years or so.
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