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MG MGB Technical - brake master cylinder: hone or polish ?

Fellow B lovers,

I am in the process of overhauling a brake master
cylinder (dual line, no servo, MGB 1970 US spec).
The inner wall looks pretty good, no pitting or deep
scratches. I was planning to have it lightly honed,
but yesterday I found an article on the Internet which
stated that Lockheed master cylinders were produced
with highly polished rather than honed inner walls,
and that the rubber cups are designed for very smooth
surfaces.
Polishing with "white jeweler's rouge" was recommended
rather than honing.
I would like to hear some more opinions on this.

Regards,

Gerald.
Gerald Belder

I'd recommend that you lightly hone it with a 180 grit flex hone (ball type) and if you want to do any polishing, use some green scotch bright to take the microscopic peaks off. I would not go any further than that.

Sean
Sean Brown

When I rebuilt mine (67 single line) I just cleaned out the bore as much as possible with soft cloth and clean fluid. It's been a year and no problems.

Bud
Bud Goetzinger

Gerald. I would use a flap sander. This is a relatively thin metal rod (1/4" or about 7mm) with is split at one end to hold a strip of sandpaper or emory cloth. The other end is chucked in an electric drill or a die grinder with a proper sized collet. Work the sander back and forth in the bore along the long axis, not stopping anywhere. If you stop, you can get a small enlargement in that area. Start off with 320 grit emery cloth, polish the inside of the cylinder, clean well using paper towels and brake fluid and dry. Then, inspect the bore. If cleaned up and smooth, go ahead and rebuild it. If you see pits, have the master cylinder re-sleeved or replace it. Just spoke to a fellow yesterday who had to go through five of these master cylinders (new from Lockeed) before he got one that would hold up. Probably worth trying to rebuild your current one rather than buy a new one. Les
Les Bengtson

Gentleman;
My method is simple. I tear down the cylinder. then take it to the sink and flush it with water. Pump some mechanic hand soap into the bore then clean it throughly with a tooth brush. Rinse it compleatly then blow dry with air. I hasen't failed me yet, Learned it from a older Mercedes mechanic back in 1972 when I worked at a Dodge/Mercedes/Vovlvo/Triumph dealer. Bob/International Auto Service
Bob Thompson

This thread was discussed between 13/11/2001 and 14/11/2001

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