Power Brake Booster Help

Hello all,

I have rebuilt/replaced from pedal to drum on my Frankie. After bleeding, adjusting (although it has 11" w/self adjusters" i am finding that the pedal still just pushes without any stop. Nada. I tested the rebuilt MC and it squirts out fluid when pushed.

I am not that familiar with booster brakes. While engine is running i pulled the vacuum hose and the engine speed up. Is that typical? Not very versed on Carb vacuum either.

Maybe i didn't adjust well enough? Do the self adjusters do that work anyways or do i still need to ensure a slight drag, then back out a start nub or two until no touch?

What else can I check/do?

 

Sounds like maybe the shoe adjustment is way loose? You manually tightened them, to get close initially... did you hit the pedal hard once or twice during the process to center everything?

Does the pedal improve if you have the e-brake on, or pump the pedal quickly?

Automatic adjusters require quite a number of hard pedal applications to have a significant effect at first. IIRC correctly, some ask for reverse stops.

I'm assuming you didn't leave out or misfit any parts. And you got all the air bled out completely.

 

Engine speed up on vacuum hose removal is normal ( basically manifold vacuum leak )

 

Is the booster new? Does it have the correct check valve it came with? Vacuum Booster Diagnostics | Know Your Parts

Booster needs manifold vacuum. Either a port at the base of the carb or direct to manifold. The rear drums need to be adjusted so you can put the drums on, then take your adjusting spoon and adjust until there is a slight drag on the drums. Ensure the adjusters are on the correct sides.

Adjust the brake arm push rod free play, but not excessive. Inch or so.

Bleed brakes.. Don't crash?

 

Did you bench bleed the master cylinder?

 

Possibilities
- push rod is not actually pushing the MC piston (hidden by the booster)
- brakes are so badly adjusted there is no resistance
- brakes at the wheels are assembled wrong so that the cylinders are not pushing on the shoes
- MC bore is full of air
- wheel cylinders are full of air
- MC seals are not holding pressure
- wheel cylinders are not holding pressure (you'd see a lot of fluid on the ground)

The booster is not connected to the fluid - it's just helping your muscles. If you connect the booster and the engine speeds up, that indicates a vacuum leak.

Likely others I'm not thinking of offhand.

 

This may help.