Brake pedal to floor soooo very slowly?

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67dartgtgo

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Could use some help here guys.
I've got a power disc conversion that works great. (SSBC)
Brakes grab and hold well with great pedal feel.
Plenty of vacuum @ 21".
My problem is that when I'm stopped with my foot on the pedal for a length of time the pedal ever so slowly pushes to the floor, bringing in the "Brake" light. I just give it a quick pump and it's hard again at the top until it continues downward in the same repetative manner.
The lines are all bled well with no air in the system and all lines are tight without any leakage.
Could there be a slight vacuum leak causing this?
Has me scratching my head....:coffee2:
 
Nope. It's defective. We are assuming you do not have a leak. Fluid leaks past a damaged cup or damage or dirt in the bore and escapes from the high pressure of the bore back up into the reservoir.
 
Okie doke....thanks. Gonna hafta get on that.
...Bri
 
Try to get the best quality master cylinder you can, preferably new (not remanufactured). RockAuto.com has a good selection I've bought a few off there with good results... Wagner is the brand that sticks in my mind but I think those are being discontinued unfortunately.

I once got a reman'd master cylinder from O'Reilly for my '70 Duster (manual front discs) and only a couple months after installing it the pedal would go straight to the floor if you didn't press on it fast enough. Typical for a rebuilt unit with a honed bore, the seals might not fit properly because the bore is just slightly too big.
 
Same deal with me on a fairly new (rebuilt) 1-pot MC. I took it apart and found the lip seal cut. The rebuilders honed the bore but didn't clean-up the sharp edge in the side of the bore.
 
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