Brakes fading

[Bradsp8]

Stock 75 but with a Tom's Brake booster/angled bracket/master cylinder. Still have drums on all 4 corners. When I'm at a stoplight my pedal slowly sinks unless I pump it. This happens to the point that if it's a long light my pedal is almost bottomed out and it starts moving forward unless or until I take my foot off and re-apply the brakes. Usually only one pump is needed but I experimented and this fading will continue indefinitely. Do I have a vacuum leak in my booster? Any other ideas I can check to solve this issue? Thanks.

 

[Broncobowsher]

Your master cylinder is bad. Fluid is passing around the seal and you have to repump to put the fluid back on the front side again. You didn't mention anything about fluid loss, which confirms the internal leakage.

 

[savage]

Did you look in between the MC and vacume cylinder to see if fluid was leaking.I put Tom's Brake booster/angled bracket/master cylinder on my 74 and one of my wheel cylinder started to leak ,I was told when you put a new MC on with old wheel cylinders the new MC makes good presuire that can cause the wheel cylindrs to leak.

 

[TwoDalesDad]

It does sound like a bad MC...but It would be wise to check all of the wheel cylinders anyway....Just for piece of mind...since your brakes are a public safety feature.....and a life or death moment...maybe prevented...