Having a problem with my power brakes. Have front disc - rear drum set up. The brake peddle feels like a "rock". There is between 13-14 inches of vacuum at idle, when fully warmed up. Although the vacuum needle does jump around quite a bit. After reading through Master Power Brakes troubleshooting section, I read that a hard peddle for a front disc - rear drum set up was caused by either a defective booster or low vacuum condition . Now the booster is completely rebuilt/replated to showroom condition by Steve Gregori at http://www.detailplating.com
So, my thought was that the vacuum is "too low" to support the power brakes. How much vacuum is everyone else pulling with their 502/502's ? :confused:

Any help sorting this out is truly appreciated. :(

Kent
'68 Malibu ZZ502/502 :D
ACES #5102 graemlins/thumbsup.gif
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My ZZ502 pulls 13" of vac at idle.
I didn't seem to notice a hard pedal when the booster was hooked to engine vac. I decided to go with a vac pump for my brakes. The ideal vac for power brakes is around 16".

Thanks for the reply. If you have 13 inches then, sounds like I have normal vacuum. Was thinking maybe I had a vacuum leak somewhere. Anyone else ?

Kent
'68 Malibu ZZ502/502 :D
ACES #5102 graemlins/thumbsup.gif

Steve rebuilt mine it lasted 600 miles.
i had to send it back and have it redone.

the booster would hold vacuum but as soon as you pushed the peddle it lost everything.

the way i found this out was i took it to Bendix, i have a friend who works there.
and i had it hooked up to their computer and bench tested.
everything was fine until you hit the peddle.
my peddle was like yours hard as a rock.

Donnie

Master Power brakes says they want 18" of vacuum. We had a 66 chevelle at my shop with a nasty cam in it , and it had 8" of vacuum. We installed one of MP'S vacuum pumps to help the brakes. It worked just fine. The pump runs on demand, not all the time, so you don't hear it.
Chip

We put a 502 Ramjet into a 60 Impala and tried the small six or seven inch booster to clear the valve cover and even with a vacuum pump you couldn't lock up the brakes. We installed a hydra-boost setup, all kinds of brakes now.

Thanks for the replies guys. Trying to keep an original appearance to the engine compartment. Hopefully I can sort this out. Any more 502's out there with a vacuum reading at idle ? :confused:

Kent
'68 Malibu ZZ502/502 :D
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