coopsvette7074

So i just took my 77 out for a drive for the second time today, but this time as i approached a set of lights the car stalls.....Brought it home and looked to see if theres a vacuum leak or anything obvious but found nothing.....When in park and i pump the brakes the rpms increase by 1000 to 1500......its a fairly stock engine with a cam and edlebrock carb....any thoughts?

Sayfoo

PB booster shot craps

coopsvette7074

Any tips for swapping that out?

yyz1970

Hate to tell you its one of the most difficult repairs
Bolts are under the dash above the brake pedal
remove the drivers seat so you can lie on your back to access the brake booster bolts under the dash

BLUE1972

Pull the seat and put milk crates alongside the sill plate with carboard on them. makes it easier on your body.


I would unplug the booster, plug the hose and see if the idle still increases , if it does not it's the booster.

doorgunner

Rookie question: Could the one-way vacuum supply valve that plugs into the front of the booster be defective?

BLUE1972

That should hold vacuum in the booster, you can pull it and you should be able to only blow through one way.

Sayfoo

It is a bit of a project to replace the booster, so, yes, make sure it is the booster before you change it.
Good tip on using milk crates to even up your working space. Definitely remove the drivers seat. Then with the right combination of extensions, universal joints, and a deep socket, you can reach the nuts. Once you break them loose, they will usually come off with your fingers. Also, tape over the universal joints so that they will remain in position, not just flop around.

Dirty Dalton

And now you've done the easy part! Getting the nuts on is a whole nother challenge. And, before you even think of sticking the replacement booster in:

1. the shaft interface between booster and master cylinder is IMPORTANT!! Some boosters come with a gizmo to facilitate getting that right.
2. Ensure that the clevis pin you have, that secures the booster 'fork' to the brake pedal, will pass thru the fork with surplus for the retaining clip. DAMHIKT!

doorgunner

Annnnd before all that....make sure the end of the rod that stabs into the booster has enough taper/or radius on the end of it so it will bottom out in the female part of the new booster. (It's rare, but sometimes the new booster is mis-matched to the brake pedal "push-rod") (Been there )

Sayfoo

There is a tool available (gizmo above) that checks the dept of the hole in the mc and the length of the rod on the booster in order to get the small clearance needed for the combo to work correctly. Use your googlefoo.

derekderek

start over and make sure you need a booster. it could be revving when you hit the brakes because it is too rich and the extra air from booster is improving the mixture. unhook and cap brake booster line. see how it runs and what engine vacuum at idle. get or borrow a vacuum pump and test the booster for leaks. it would suck (pun intended) to replace booster with a new one and have the same problem.