Head scratcher hard pedal

[Roger63]

So I got the new engine in and running perfectly, I knew I would have low vacuum with my cam choice. I tested the brakes and as I thought I didn't have enough vacuum for proper brake performance. I purchased an aftermarket vacuum cannister with a gauge, installed with all new hoses and retested. No change, my next test was to see how much vacuum I could build, it built 20 inches of vacuum, plenty right? So I let it sit overnight and rechecked. It held 19 inches of vacuum overnight. Any ideas?

 

[jamie]

Sounds like your booster is bad.

 

[Curiousyellow71]

11-12 lbs a booster should work yet. Sounds like booster is bad or your gauge is bad.

 

[MIKESPOLARA]

Did you measure vacuum at lowest possible idle speed, no vac advance etc. Might not have 20". Easy to read 20" if you bring speed up, close carb butterflies then it will measure high
If its 14" or so the booster should work OK then bad booster

 

[1 Wild R/T]

What booster are you running? OE? Or a new repo?

 

[Roger63]

What booster are you running? OE? Or a new repo?

It's a repop that came on the car

 

[Roger63]

Did you measure vacuum at lowest possible idle speed, no vac advance etc. Might not have 20". Easy to read 20" if you bring speed up, close carb butterflies then it will measure high
If its 14" or so the booster should work OK then bad booster

At idle with no vacuum in the tank it will build about 7 inches of vacuum. It won't build anymore without raising the rpm.

 

[jamie]

Get your 20 inches of vacuum,shut car off and pull check valve out of grommet on booster,it should hiss/leak vacuum.

 

[1 Wild R/T]

If it's this style....

It's probably bad... I had a customer with one like that, I replaced it, still no brakes, rechecked everything & convinced myself I must have gotten a second bad booster... Got a third... Still rock hard pedal... Triple checked everything, was talking to a friend who builds allot of hotrods for customers... He tells me he's replaced over twenty of them & refuses to do it anymore... He only uses rebuilt OE boosters.... I got an OE booster for my customers car, had Dewey rebuild it & the brakes were perfect.... I'll never waste my time on one of those again...

 

[Roger63]

Well apparently I'm gonna have to follow 1 Wild R/T advice. Replaced master cylinder booster bled the system but not much improvement.

 

[RemCharger]

Is that the Chevy corvette type one that comes in all the kits??
Junk

 

[Roger63]

Is that the Chevy corvette type one that comes in all the kits??
Junk

I don't know, when I bought it I was told it was for my car