This is a weird one for me. Overhauled the brakes on my 66 this spring and bought a reproduction master cylinder since the bowl in the old one was pretty rusty. The new one had a tapped port in the boss on the bottom with a plug in it that the old one didn’t have. The boss was there but no port. Tightened the plug securely, bled it, put it on the car, bled the brakes, etc. After every drive I would find fluid collecting on the bottom of the boss and no sign of it on the line or upper MC body.
So I pulled the plug, applied teflon tape, reinstalled and still a leak.
Pulled the plug again, pulled the plug, removed the tape, put Gas Cinch thread sealer, tightened up and still a leak.
Pulled the plug, cleaned out the Gas Cinch, applied Permatex #2 and tightened up and still a leak.
Pulled the plug again, put a small o-ring in the bottom, reinstalled the plug and still a leak, always on the bottom of the boss.
Bought another reproduction MC from different source and Hallelujah, the boss is not tapped, and is just like the old one. I like the finish of the cap on the first one better so I swapped it to the new one. Bled the MC, installed, bled brakes, went for drive. Dry when I return. Go to the garage the next day and bottom surface of boss is wet. No sign of any wetness on the line, the line adaptor, the cap or the upper MC body. WTH!
OK, I can’t see any sign of fluid on the upper body but the cap must be seeping slowly. So, I cut a 3/16” circle of cork gasket to glue to the bottom of the cardboard gasket provided for the cap and I put a sealing washer on the center bolt. Tighten it down. Go for a drive, dry when I return and later in the afternoon, next morning the bottom is wet again. Sometimes it’s even on the second day after a drive I find fluid.
Tighten the cap bolt tighter, drive, wet the next day on the bottom of the boss.
Tighten the cap tighter, drive, wet the next day on the bottom of the boss.
Repeat tightening but by now I realize I’m collapsing the cap.
Pull the silver cad cap out that came with this MC and installed it. Pushed the top out on the first repro MC for posterity sake. Haven’t driven it yet - so damn hot to go for a drive in an all black car.
Has anyone run into this??? There is absolutely no sign of leakage that I can find. The fluid just mysteriously appears after a day, sometimes 2 days on the bottom of the boss. The line is tight but even if it were a line I believe I would see fluid immediately after a drive from high line pressures, not a day or two later. No sign of leak from the rear from either MC and it would have to run uphill to get on the boss. I thought about a casting leak but what are the chances of 2 MCs with the same casting flaw? Besides after a couple days I can clean the bottom off and it will then be dry until I drive it again.
I think I’m going to see if I can find an o-ring that fits the inner perimeter of the cap to seal on the MC bowl lip. But I’ll have to be careful that it doesn’t squeeze out of position.
Any ideas what’s going on and how to stop?
So I pulled the plug, applied teflon tape, reinstalled and still a leak.
Pulled the plug again, pulled the plug, removed the tape, put Gas Cinch thread sealer, tightened up and still a leak.
Pulled the plug, cleaned out the Gas Cinch, applied Permatex #2 and tightened up and still a leak.
Pulled the plug again, put a small o-ring in the bottom, reinstalled the plug and still a leak, always on the bottom of the boss.
Bought another reproduction MC from different source and Hallelujah, the boss is not tapped, and is just like the old one. I like the finish of the cap on the first one better so I swapped it to the new one. Bled the MC, installed, bled brakes, went for drive. Dry when I return. Go to the garage the next day and bottom surface of boss is wet. No sign of any wetness on the line, the line adaptor, the cap or the upper MC body. WTH!
OK, I can’t see any sign of fluid on the upper body but the cap must be seeping slowly. So, I cut a 3/16” circle of cork gasket to glue to the bottom of the cardboard gasket provided for the cap and I put a sealing washer on the center bolt. Tighten it down. Go for a drive, dry when I return and later in the afternoon, next morning the bottom is wet again. Sometimes it’s even on the second day after a drive I find fluid.
Tighten the cap bolt tighter, drive, wet the next day on the bottom of the boss.
Tighten the cap tighter, drive, wet the next day on the bottom of the boss.
Repeat tightening but by now I realize I’m collapsing the cap.
Pull the silver cad cap out that came with this MC and installed it. Pushed the top out on the first repro MC for posterity sake. Haven’t driven it yet - so damn hot to go for a drive in an all black car.
Has anyone run into this??? There is absolutely no sign of leakage that I can find. The fluid just mysteriously appears after a day, sometimes 2 days on the bottom of the boss. The line is tight but even if it were a line I believe I would see fluid immediately after a drive from high line pressures, not a day or two later. No sign of leak from the rear from either MC and it would have to run uphill to get on the boss. I thought about a casting leak but what are the chances of 2 MCs with the same casting flaw? Besides after a couple days I can clean the bottom off and it will then be dry until I drive it again.
I think I’m going to see if I can find an o-ring that fits the inner perimeter of the cap to seal on the MC bowl lip. But I’ll have to be careful that it doesn’t squeeze out of position.
Any ideas what’s going on and how to stop?
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