Brake problem.....

[74Charger]

Ok, heres my deal.  I have a 74 charger 440 with a 509 cam / tunnel ram setup. Because of the cam I have.  I had to get a MP vacuum pump installed.  But here still lies my problem.  I still have horrible brakes.  And the vacuum pump stays running.  It will not shut off.  If I plug the end of the hose to the pump it shuts off.  So that rulles out that the vacuum pump is faulty.  Brakes are not that old.  Plenty of pad almost like new.  One way check valve new.  Vacuum hose all new.  Brakes have been bled properly twice.  So I think I have a leak in my booster?  But I was told if it was the booster.  The brake pedal would be up high and be very hard.  Is this true?  Instead when I push on the brakes they almost go to the floor before they start to stop.  If I pump the brakes.  The pedal seems to come up a little for a second.  But then fades before it almost goes to the floor and then the brakes start to slowly work.  Would this be along the lines of air in the system?  Or a faulty master cylinder?  This is very frustrating.  Any suggestions would be greatly appreciated.

[69BlackChargerRT]

I had the same problem with my '69.  I thus went to manual brakes, but as poor as they were, I am switching back to power.  I suspected a leak in the booster (as the pump would run then shut off for a few seconds then switch back on).  My vacuum can is fine, therefore I had the booster rebuilt and am in the process of finishing the task.  I will let you know asap whether the booster leak was the culprit.  Good luck.

[Chryco Psycho]

it must be a bad diaphragm in the booster creating an inernal leak which is hurting the brake performance

[74Charger]

it must be a bad diaphragm in the booster creating an inernal leak which is hurting the brake performance

If thats the case.  Can it be rebuilt?  Are they worth getting rebuilt?  Or just buy a new one?  I know the local Checkers / Autozone / Napa auto stores has them.  If I have to get a new one.  Are there huge differences between different brands? 

[Chryco Psycho]

we have a rebuilder in town , & yes they can be rebuilt but I guess it depends on the overall condition of your booster , it may be just as good to replace it 

[71charger_fan]

"I thus went to manual brakes, but as poor as they were, I am switching back to power"

Power brakes are not power brakes, they are power assisted brakes. They don't develop any more brake line pressure than manual brakes. If your manual brakes weren't stopping you I suspect a problem other than the lack of a booster.