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Hey all! I can't seem to find a search answer so I thought I'd post up and get some opinions. This is probably a service tech question, but I'll solicit from those with experience. First of all let me say that I'm mechanically competent and not afraid to work on a motorcycle. Do it all the time, although not for a living. This question, though, has me thinking.

I recently purchased a bike with 55K miles on it, and the brake master cylinder is beginning to get tired. I have plans to rebuild the Master, along with the clutch cylinder for good measure, but when I spoke to my local service department about it they recommended a replacement. The main reason being that the bore is probably worn out. Now, the only reason I can see replacing a master cylinder (as opposed to rebuilding) is down the to anodized coating wearing off the inside of the cylinder bore. (I am traveling away from the bike, or I'd already have it apart and inspected by now.) I've not put 55K miles on a modern bike, so I reach out to ask this question:

What is the lifespan of a modern Master Cylinder?

I would expect to rebuild one about every 25K miles (or sooner), but there must be a point at which the master cylinder bore will wear. How long?

-Tom
 

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You don't say what bike or if you have OEM parts, the masters are not all the same. Not sure about life expectancy from the bore, but I can tell you that most of the OEM Brembo masters, especially from the 916 / 996 era, do not have rebuild kits readily available. Not sure about older or newer. Some sites (Gotham for one) have kits listed, but only for few masters. People have remarked that KTM may have a kit for a Ducati OEM fit Brembo master, but I have not followed those leads. I had a 996 style clutch master go out last season. Looked for a while for a kit, but no luck. I just picked up another off eBay. I pulled my old one apart and there really is no reason you couldn't rebuild it if kits were available. Didn't look too closely at the bore for wear, but nothing more than a few seals and springs just like the many old automotive clutch and brake masters I had rebuilt in my youth.
 

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It depends. Master Brake might "go" if the fluid was very old, and then bled in new fluid. I say BRAKE, because the entire stroke never gets used on a master, until you go to bleed the system. Then, you are asking the seals to pass over areas that are (were) still virgin.

Sometimes this crud can ruin the seals...

Learned this with cars many years ago...
 
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