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Thread: rebuild or replace

  1. #1
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    rebuild or replace

    I've got an 83 R100RT the has a bad rear master cylinder has anyone had any luck rebuilding those or should I just replace it?

  2. #2
    Administrator 20774's Avatar
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    What's bad about it? So, it depends...there are services that will overhaul or sleeve a master cylinder if you want to keep what you have. Or you can buy knew and be up and running more quickly and confidently.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
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    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

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    Registered User kgadley01's Avatar
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    I had this problem a couple of years ago. I replaced mine with a new unit. You may want to check with Beemer Boneyard to save yourself some money...
    AKA SNAPGADGET
    Lifes too short to ride an ugly Motorcycle

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    I'm not sure how bad it is all I know is it will not build and pressure.

  5. #5
    ONE LESS HARLEY 04r1150rs's Avatar
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    if you rebuild give yourself a 50% chance of it holding up for a year or less....just my experience on rebuilding MC's. Check with Motobins for a price of a new one. They are usually quite a bit cheaper than the stateside stealerships, even considering the shipping and Brit LBS to USD exchange.
    Richard
    2004 R1150RS
    1984 R80 G/S
    2003 Suzuki DRZ 400S

  6. #6
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    Quote Originally Posted by 04R1150RS View Post
    if you rebuild give yourself a 50% chance of it holding up for a year or less....just my experience on rebuilding MC's
    I rebuilt one 9 years ago, and another 6 years, and they're still holding up fine. So from my experience, I'd say the OP has a 200% chance of it holding up.

    I have another one on my bench right now waiting on a rebuild.

  7. #7
    ONE LESS HARLEY 04r1150rs's Avatar
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    well obviously your results may vary... I've taken great care to lightly sanded or honed those being rebuilt and inspected inner surfaces for nicks and such still have had them leak. I don't rebuild MC's anymore due to past experience w/ cars and motorcycles but have done many brake calipers with great results...Just something to take into consideration, that rebuilding doesn't guarantee it will be leak free. Rebuilding is a gamble and may or may not work. If the rebuild doesn't work then you out the price of a rebuild kit and MC and maybe a ruined gas tank, if it works then just the rebuild kit.

    If I were getting paid to repair a customer's MC, I wouldn't want to take a gamble that the rebuild would work and potentially have eat the labor and explain why now the customer will have to buy a MC because the rebuilt one leaked. What rebuild it again for free or have the customer by a new MC on top of what was already charged because I have a 200% success rate w/ rebuilding hydraulics...
    Richard
    2004 R1150RS
    1984 R80 G/S
    2003 Suzuki DRZ 400S

  8. #8
    Rally Rat
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    related note, what are people's thoughts on re-sleeving master cylinders?

    I know a guy who can get it done for about a hundred bucks... Wondering if it's worth it.

  9. #9
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    Is he able to install the sleeve and have all the orifices line up? I don't know how much a new rear master is. But with 100 bucks, you should be close.

  10. #10
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    this was for a front master. specifically a dual disk. I've not seen the guy's work, but He comes highly recommended.

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    "Rebuilding" is quite a general term and can reach from just cleaning to changing parts to re-sleeving. If all that is need to use a "repair kit" and put a new plunger and seals in the MC, I would do this and expect the unit to last a while.
    Re-sleeving to me is tricky and I hesitate to trust the work and the cost may be very close to buying a new part.
    Early K-bikes ( and maybe R bikes at that time too) had a problem with the front MC, where the anodized plunger wore the soft bore out. BMW was selling a rebuild kit in Europe, but not in the U.S. Here they listed the complete assembly for replacement. Mainly because the replacement and later original equipment parts had a hard bore. I brought several repair kits from Germany at one time and provided friends in need with them. Some worked and lasted, some did not. I put one in my 1990 K1 and it lasted for two years and then started leaking again. I replaced the complete unit then.

  12. #12
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    Quote Originally Posted by Roguetek View Post
    related note, what are people's thoughts on re-sleeving master cylinders?

    I know a guy who can get it done for about a hundred bucks... Wondering if it's worth it.
    In terms of working on old stuff like we do, I was once told, "See what you can get away with." Yeah, we're dealing with brakes, but if we're competent enough to know what a master cylinder is, we're competent enough to determine if a job is safe or not.

    The master cylinder I just rebuilt is honestly a bit rough. If my rebuild success rate drops, I'll shoot for re-sleeving this one. Why not? Is your guy a friend, an airhead mechanic, a machine shop or what? Heck, I have a couple mills and lathes at home, so I might even try the job myself (some day).

    Assuming your master cylinder in question is from your '77 R100RS listed in your profile, MAXBMW has a new one for $387.00 and a rebuild kit for $67.55. If it doesn't need to be re-sleeved, $67.55 is not a bad price for a good working master cylinder. If you need to get it re-sleeved for $100, you'll have an essentially new master cylinder for about $167.. still 43% of the new price.

    I say one of us should give it a shot and let the rest know how it goes.

  13. #13
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    Thanks for all the input but being I will be riding my wife on the back I opted for a new one.

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