Weird power brake problem.

[71RRHI]

On my 70 Coronet 4 speed with power brakes. If the car been sitting let say over night or more. I start the car, put it gear and pull it out the garage, the first time I press the brakes there is no power assist. If I move the car and hit the brakes again they operate perfectly. I can drive around all day no problems brakes work great. If I park the car for the night, next day same thing. If I press the brakes before moving the car then everything works properly.
My 71 RR has power brakes and I don't have this issue. But it is an automatic, so I press the brake before putting it in gear. My other cars have manual brakes.
Is this normal and I just didn't notice it until I got the 4 speed? If it's not normal, any suggestions on what to check?

 

[twecomm]

You may have a vacuum leak or brake booster going bad.

 

[Tinker67]

Booster check valve?

 

[Doorkicker]

i agree with the others... think it's a check valve. but I'm curious... when you first hit the brake pedal... is it hard and no movement, or does it go to the floor?

 

[71RRHI]

i agree with the others... think it's a check valve. but I'm curious... when you first hit the brake pedal... is it hard and no movement, or does it go to the floor?

The pedal is hard, same feeling as stopping a power brake car that's not running.

 

[Doorkicker]

The pedal is hard, same feeling as stopping a power brake car that's not running.

Yeah, that sounds like a check valve issue or (worse) a leaky booster. I would take little steps...start with checking the vacuum hose from the booster to the intake or base of the carb to make sure you don't have a leak, crack, whatever. Next, assuming the hose is ok, I would put a new check valve in the booster. If that doesn't work...I'd put a small amount of air pressure in the booster and listen for leaks (only after sitting for a while).

The fact that after running for a few minutes it goes back to normal... that's the engine pulling a new vacuum in the booster and the leak is slower than the ability to create and retain a vacuum while the engine is running.

Anyway, just my $0.02.

 

[twecomm]

You might want to get a hand operated vacuum pump with gauge on it and pull a vacuum on the booster and see if it holds.

 

[71RRHI]

You might want to get a hand operated vacuum pump with gauge on it and pull a vacuum on the booster and see if it holds.

I can do that, how long should the booster hold vacuum? The hardest thing for me grasp is first press of the brake pedal no power assist. Let go of pedal and push again full power assist.

 

[71RRHI]

Pulled the check valve, seems good, can not blow into it, but can blow out of it.