Brake Pedal Sink Down

[Ron H]

A disc brake conversion I had done left me with many problems to rework such as the pedal height and brake switch contact among other things. The conversion included manual to power brakes. I thought I got it pretty close; but the pedal return (full return) remained an irritation. I took the easy route for time being while I could determine better solutions by putting in a return spring. Be damned if even this hasn't worked. Pedal seems to suck down after car sits and seems like I have poor vacuum until motor warms up a bit. I have a slightly modified cam after engine rebuild I've heard can play havoc with vacuum. Anyone encountered this sort of problem?

 

[black64]

Sounds like you are losing vacuum from booster after shut down. Maybe check valve not right or hose loose. You should have firm pedal when you first start it with foot on brake pedal should drop some when vacuum is present from running engine. What is your vacuum at idle? You say poor vacuum until car warms up maybe a vacuum leak. What brake kit did you use?

 

[Mike67]

Where is your vac source coming from, carb or manifold?

 

[Ron H]

SSBC kit for '65-'74 B & E body (car is '63 Fury). The vac line is off the intake port not carb. Line seems tight. I'll have to check vac since motor rebuild..

 

[5.7 hemi]

You should be looking for at the minimum 15 inches of vacuum for power brakes.

 

[coloradodave]

You should be looking for at the minimum 15 inches of vacuum for power brakes.

Hey Zack, I have 4 wheel power disc brakes ( 76 A body front, Moser rear) utilizing a Corvette master cylinder and 8" booster. I have 12" of vacuum and awesome brakes. My experience...

 

[5.7 hemi]

That’s cool! What size mc you using?

I was just passing along stuff I’ve read over the years. Hmm, now I’m gonna have to do more research.

 

[beanhead]

I had that problem once due to rear drums being out of adjustment, on a manual drum/disc setup..I'd get out of the car and the brake lights would be on..it throws the whole system out of whack

 

[Ron H]

Now that I have car on stands (won't say "jack" anymore fearing retribution) I'll see what the rear brakes look like but the matter seems like a vacuum loss; but figuring check all out. There's also a good degree of pedal travel before getting the brakes that could be needing new shoes or even drums; rear drums are old. The problem I have from doing more reading is sort of opposite folks more often have with brakes, my pedal sinks when car is off while others have that happen when car's running. I've been told to look at the gap (rod) between the booster and cylinder as a culprit as well. Don't think the SSBC instructions made mention of this will look again.