By: jpattonfamily

jpattonfamily — Sat, 18 Jul 2009 10:05:55 +0000

brake booster diafram leaks better to replace whole unit

By: musiclicker

musiclicker — Fri, 17 Jul 2009 06:13:53 +0000

I own a shop, and have my share of dealings with brakes. First of all lets think about this: The brakes are mechanical, and work just fine until you turn the engine on, so this indicates the master cylinder is fine, and the problem somehow lies within the brake booster. Don’t think it is bad just yet! The vacuum line that supplies the booster may be the problem. There is a check valve in the line where it plugs into the booster. If its bad, then the booster will rob all the vacuum when you start the engine, and the pedal comes back once it runs some, so I think this valve may be bad. Take it out, and see if it hold pressure one way but not the other. If so, then its working right. With the engine running, unplug the hose, and it should kill the engine, or very near cause it to stop running. There may not be enough vacuum on the line, and it could be plugged up under the carburetor with carbon. You should be able to run a clothes hanger into it to open it up. I’ve seen some that had to be drilled out because the stuff was so hard, and had accumulated there for years. Either way… make sure you have a good supply. Make sure you have a good hose that doesn’t leak, and the valve that plugs into the booster where the hose plugs onto should be able to suck air out of the booster, but not suck air the other way. In other words it lets air flow one way, but not the other. Since this is vacuum it should flow out of the booster, and not into the booster because you are dealing with vacuum, and not air pressure. If you determine the supply is good, and the valve is good, then if it doesn’t work replace the booster. It must be one like what comes on it, or you could have a problem with the length on the rod for the master cylinder. You could even have the wrong booster on it.
Glad to help out, Good luck!!!

By: grandnational_man

grandnational_man — Tue, 14 Jul 2009 16:38:13 +0000

The brake booster is bad.
You will need to buy a reman unit. It should be about $75.00 to $150.00 and you won’t need to bleed the brakes again either.

By: eldoradodave

eldoradodave — Sat, 11 Jul 2009 06:17:31 +0000

Its in the vacuum booster. Diafram ,maybe but their is a kit to rebuild it

Comments on: Does anyone know anything about the brake system of a 77\’ Chevy truck?

By: jpattonfamily

By: musiclicker

By: grandnational_man

By: eldoradodave