I have a 72 Chevelle with power disc brakes in the front and drum brakes in the rear. How many inches of manifold vacum will be needed to still be able to operate my power brakes? I have no problem using a vaccum resivouir if it will be required. The engine I'm building will have 14-18 inches of manifold vaccum will this be enough to still operate my power brakes?

Brandon

hey Brandon the 350 in my 81 only makes around 15 at idle and the brakes work just fine. Work even better since I put on another booster...

Thanks for the response JJ, is the 350 in your 81 fairly stock? does it have a slight cam in it? To bad you weren't able to make to the Laurel 4th of July show, I enjoy talking with you and your parents and we don't usually meet up to often. I know you must have called Tom there like five times since I was sitting next to him at the show. ;)

Brandon

This issue was a tricky one for me - partly because not all my dogs are barking when it comes to wrenching. Even with my 11" booster, single piston front discs, big rear drums, I required 18" to make them feel solid, 20" to make them feel almost like late model car brakes - which I characterize as dependable. I set the benchmark comparison against the brakes in my wife's small suv. ABS sensitivity aside, I believe brakes should be, well, brakes! I wasn't happy with hard pedal, soft pedal, "you'll get used to it", etc, etc. The only metric I allowed to change in comparing the two cars was brake pedal application timing - I already know I have to hit the pedal a little sooner than a modern brake system (Lord knows we have all gotten used new millenium stopping distances). That said, the best result I got was from using a supplemental electric vacuum pump that also has a t-feed off the manifold. By itself, the pump can give me a constant 25", I have it dialed into 22" and the brakes feel VERY dependable. Without the pump on, the brakes still work, but I have to allow an extra second or two lest I tap whomever happens to be in front of me. Also, without the pump, the pedal will be on the floor by the time I come to a stop if I have to make a relatively quick stop (like if somebody cuts me off a couple car lengths too soon). The brakes will stop the car - no doubt about that. The vacuum pump adds what I felt was a necessary level of insurance. Just my opinion, though. There are plenty of folks on this site and others that achieve excellent braking characteristics with straight manual brakes. In the end, it was up to me as to what I was comfortable with when stopping a 550hp (before rebuild) heavy.

Hey Brandon
You making it to the Big M saturday? I don't know if I'll have the wagon there but I will be there. The motor in the wagon is the one that was in my yellow 72... it has the 327/350HP cam in it.

Nope I wasn't able to make it, how was the turn out.

dunno had something else come up

mikehartwell

I was wondering what kind of vacuum pump you have as well as cost and where to get one. I added a vacuum cannister to mine but I am still not happy with it. Also you said the pump would supply 25 but you had yours on 22, does that mean there is an adjustment on the pump?