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Weird power brake problem.

71RRHI

71RRHI

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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?
 
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?
 
Doorkicker said:
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?
Click to expand...
The pedal is hard, same feeling as stopping a power brake car that's not running.
 
71RRHI said:
The pedal is hard, same feeling as stopping a power brake car that's not running.
Click to expand...
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.
 
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.
 
twecomm said:
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.
Click to expand...
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.
 
Pulled the check valve, seems good, can not blow into it, but can blow out of it.
 
Curious did you ever find the issue?
 
Moparfiend said:
Curious did you ever find the issue?
Click to expand...
The problem is since the car is a 4 speed, sitting in the garage, I put the car in neutral, start the car, back out of the garage. First time I hit the brake there is no power assist. If I release the clutch and move again. Hit the brake and have power assist and works great all day of driving.
I have never figured out why. All I have been doing is starting the car in neutral, press and release the brake pedal. Put it gear, back out of the garage and brakes work normal.

Don Frelier said:
Yeah, What happened after the blow job?
Click to expand...

eldubb440 said:
he probably fell asleep
Click to expand...
That does usually happen.

lemondana said:
How big of a cam do you have in it?
Click to expand...
I don't now the exact specs of the cam. But I believe its stock spec, or very mild above stock. I put a vacuum guage on the vacuum hose going to the booster, and have 15-17" of vacuum at idle.
 
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