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MG MGB Technical - master cylinder rebuild

Well I did it...I rebuilt the dual line/non-servo MC on my '74 B; and inspite of all the hype, I thought it was rather easy...I bench bled it last night and all seems fine...this leaks...And I've been worried about that...While I was there, I did the Clutch MC, as well (real easy)...

Now the question, if the brake MC is going to leak, do they normally wait until installed?...

Well, Pete, I don't want to be negative, but after spending the bucks to get mine resleeved and then carefully rebuilding it, it started leaking slowly out the front after a month or so. This is after holding up thru numerous bouts of bleeding using various methods. I took it apart again, and installed another kit that I had on hand. At that time, I thought that I'd probably damaged some part in reassembly. Then, on a subsequent thread on this list, I read that the piston had to be pristine; it had to look like chrome, or it'll leak, cause it's used as a seal. Wish that I'd read that before beginning, 'cause mine was far from pristine. Now, since my car is 'still' in construction, I'm debating whether to try refilling this one and trying it again, or just buying new. The cleanup after the last episode isn't something that I want to repeat, what with having to take all the supporting pieces apart, buying new gaskets, and repainting of the surrounding area. My stubborn streak says 'try it again', but I'm leaning toward a new master so as to avoid all that. So, for the short answer, 'yes', it can wait a bit to start leaking. Best, Joe
Joe Ullman

Joe is correct that if the chrome has any pitting or scratches in it it may eventually leak. I rebuilt mine in 1991 and it is still fine.
John H

i've given up rebuilding anything related to brakes- it's just not worth a possible failure. I gladly spent the money when needed for new master cylinders for the B and the midget.

don g

my piston is chinny pits or deep scratches...

Pete, yours may be successful. It's not brain surgery, and I'm obviously in favor of the DIY approach if you can. if your scratches really aren't 'deep', it may hold. Lucky you, with a chinny chrome piston; wish I had one! Joe
Joe Ullman

Joe, I'm losing my marbles...chinny?...The piston is chrome and mirror-like...and I'm hoping it behaves...Thx...and I let you know...If it leaks, the best prices for a new unit seem to be with Apple...

This thread was discussed between 04/08/2008 and 05/08/2008

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