Hell everyone, I seem to be having trouble with my 74 Chevy truck. It starts up great, idles great and runs fine, except that "sometimes" it wants to die upon coming to a stop. Floats seem to be good, 2 turns out (adjusted w/vacuum gauge). I have noticed that the vacuum hose going to the booster was cavitated, my brakes are not that great, goes pretty close to the floor. And I notice a slight change in the RPM once the pedal is depressed. If the booster was bad, wouldn't the brakes be hard to push? And if the master cylinder was bad wouldn't they would go to the floor, right? So, my question is, Can a bad master cylinder cause the engine to die upon stopping? Maybe a bad diaphram between the booster and master cylinder? Truck has 327, Holley 600cfm (4160), (4.5 powervalve or 6.5 same problem), 8 degress BTDC, HEI w/acell supercoil, Elgin 280/280, .443/.433 cam, TH350. Thanks for any help.

The booster can leak when the brakes are applied. Plug the line and see if RPM change goes away. Change the hose if it is sucking flat, also check the check-valve that goes into the booster. both are cheap. You will most likely have to replace the booster. I know at one time you could get it separate from the master cylinder. Cheaper that way, but check the price it might not be much difference.

Richard

Thanks for the reply. I already changed the hose, I had a fuel line for the vacuum hose and I thought that it was too flimsy, but problem still exist with respect to the stalling. Just to make sure we are on the same page, when I spoke of the "booster" I am refering to the big round thing that the master cylinder mounts to, where the vacuum hose connects. I don't have a check valve on it, it is just a 90 degree nipple that fits into a rubber gromet. Yes, you can get them separate, master cylinder $14.00 and Booster $79.00. Not too bad.

I thought they had ta check valve by then. I think it is the 90 fitting you are talking about is the check valve. The Booster is the big thing on the back of the master cylinder. They will leak differently. Sometimes they just leak other times it is only when you apply the brakes. With the truck just idling apply the brakes and see if the idle changes. Then pull the hose to the booster and plug it with a bolt or something and do the same. If the idle only changes with everything hooked up, the booster is leaking inside. I have seen those like that too many times to count. It is just a big rubber blader and wares out. It is over 30 years old now. It could be the original.
Richard

Thank you, PapaG. I am going out to do that right now. Very informative reply. Thanks.