Need help with my brakes

[1972 orange c10]

I hope someone here can help me figure my brakes out. My brake pedal has gotten really hard to push since i took my qjet off and put a holley 670 strret avenger. I just thought it was the booster so i replaced the booster and mc and bled the brakes and it was good for a day or so and now its hard again. I took proportioning valve off a parts truck i have and it didnt help. Could the holley be sucking more vacum than the qjet. If anybody could help me i would appreciate and by the way this is a awesome site i get on here everynight and get in trouble for being on computer too long. Thanks morgan

[texanidiot25]

Sounds like there's no vacuum getting to the booster from the new carb... As I know nothing about holly's, have you tried swapping carbs, or where the booster plugs into for vacuum?

There should be no reason why a holly would affect manifold vacuum unless the booster is connected some place else.

[72Much]

Run the engine for a few mins and pull the hose from the booster. Should hear a burst of air when you do. This will let you know if the motor is feeding enough vacuum for your brakes.

[1972 orange c10]

Thanks i will try that in the morning i have just got done doing a complete brake job on my four runner and messed with the truck. I have never had that kind of problems with brakes before. I do know the truck needs front brake hoses they are getting dry rotted but i didnt think that would have anything to do with a ahrd brake pedal. Thanks for the suggestions. Morgan

[spinning wheels]

Disconnect the vacuum hose to the booster. Insert a vacuum gauge into the hose, coming from the engine. You should be getting around 15 inches of vacuum.

Also check the valve that plugs into the booster. Its that small, round white plastic part, where you connect the vacuum hose to. They can go bad and not allow your motor to, in a word, suck. Its a one way valve.

Also, there is a small round rubber seal where the MC mates up to the booster. Check to see if it is there. You will need it. I was missing mine and the booster would not work. Felt like I had manual brakes and the pedal was hard as a rock.

Good luck