Master Cylinder Bore

norton said

I need to get a Master Cylinder, for my 1972 Duster. This is a factory H-Code car, with manual drum brakes all around. Every supplier site that I look on asks about the Bore. Is there any way of knowing this without removing the old Cylinder. The car stops good with the old one, I just can't seem to get the lid to stop leaking. I replaced the gasket with a new one but it leaks even worse.

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On several occasions like yours, I found the brake system to have air in it, and when the brake pedal is released, there is a violent fountain of fluid shoots up against the cap, and some migrates under the cap. I know some that should know better will disagree, but that has been my experience, and bleeding the air out of the system cured the issue, not a new seal, top, or M/C.

Want to check it, have a friend pump the brakes a few times and hold the pedal down, THEN remove the cap and have the pedal released, if you get a prolonged fountain of fluid squirting back into the M/C, then you need to stop the fluid return, by adjusting brakes, and bleeding.. jmo

PS, have plenty of water nearby, to immediately rinse any spilled fluid off the paint, as brake fluid is excellent paint remover.

hope it helps