The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: joshr65 on September 22, 2008, 11:30:33 AM
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Hi,
Every few days I notice on drop of brake fluid on my fuel tank. Where do these Master Cylinders leak from usually? I cleaned it off to check but don't see the leak. It must be very small. The brake feels fine and not mushy.
Thanks,
Josh
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Brake fluid will strip the paint off the tank and the brake lever/throttle assembly if allowed to continue. If you have the round type master cylinders, those often seem to leak around the base of the plastic reservoir, that "sits" into the metal alloy base. If this is the case, there often isn't a good way to repair them and they usually get replaced outright. The rectangular ones (from 1981 -> later) can leak from the base where the plastic reservoir sits into the allow base as well, though leaks there are often due to
failure of a small rubber O ring, which can be replaced. Both styles can also leak from the end of the plunger(where the brake lever pushes in on the end of the piston).
Look carefully in these areas for signs of moisture. Sometimes a spritz of talcum powder helps to detect moist surfaces (and give your "baby" a fresh clean smell) !
There are rebuild kits available for approx ~$50 US (last I checked) for the rectangular ones - they come with several different diameters of piston, so you must get the one that matches what is on your bike. There is a number that is stamped into the metal housing, usually toward the front/lower side that will say something like "15" or "12" or "13", etc.. This is the size (Diameter) of the piston in millimeters and is the size of the rebuild kit you should get if you are going to try to rebuild/repair yours. Before attempting a rebuild, you should probably take yours apart and check the condition of the bore (inside where the piston does its work). If it is heavily corroded and not shiny/smooth you may be better off ordering a new M/C assembly for around $150, as the replacement parts will only last a little while in a corroded bore. You can't clean up that corrosion easily - scratching the surface in there with something like steel wool will cause further issues down the road..
Anyplace that the brake fluid has gotten onto you should clean with water and some sort of soap - any brake fluid residue will damage the paint over time if allowed to sit there.
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Thanks for all the info! Appears to be leaking from lever plunger. The bike has only 15K on it so hopefully just a seal went. Will check it out further.
Josh
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Unfortunately it'll cost you about $50 to find out! You have to buy the whole rebuild kit (rubber bits, spring, piston) as you can't buy just the rubber stuff - AFAIK. >:( In all of the cylinders I've ever rebuilt I have never seen a "bad" piston, but they're gonna get yer money fer one anyway. [smiley=furious3.gif]
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Well that's fine. At least I will know it is done. What's a good source for the kit?
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Most BMW dealers or independent repair shops can order these for you, or you can get them at a number of online sources, depending on where you live.
If in Europe/Great Britain - order from Motobins. IF in the US of A, check out Bob's BMW, or Chicago BMW, or Capitalcycle. All these places have websites with parts info -
I tend to order a number of things from Capitalcycle - you can check out their website (though the prices there are outdated) or give them a call. I also have had good service with Bob's BMW.
I noticed that one can order just the plunger, or just the bellows for the main reservoir, but the rubber bits that go around the plunger are not for sale separately.
You may find that having a new plunger and other seals is a good idea anyhow.
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Unless you are in a big hurry Chicago BMW (http://www.chicagobmwmotorcycles.com) will give you the best price at 20% off current list price. I believe the only things I have ever bought from Bob's were at straight list price and my local dealer charges list PLUS! Is it a wonder I never buy anything from them?
The advice about inspecting the bore is valid, though. If you do wind up needing a new cylinder contact me before tossing out your old one, I have an idea and need something to experiment on...
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If you do wind up needing a new cylinder contact me before tossing out your old one, I have an idea and need something to experiment on...
aaah, the old "re-sleeving" investigation ?? In theory at least, it should work if you can get a good tight seal at the passageways to the reservoir..
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That's my thinking. I know automotive brake restoration specialists sleeve cylinders in brass and I remember seeing ads from a vintage Corvette brake joint that sleeved 'Vette cylinders with stainless steel. I'm pretty confident in my ability to sleeve a cylinder but the rubber bits are still an issue... But just think, sleeved in stainless you'd never have to worry about it going south on ya...