Help Needed Need help locating problems with brakes

[smokin joe]

When ever I apply the brakes they work fine. BUT if I let the pedal up and jam it down again RIGHT AWAY the pedal is rock hard and my truck does not hardly stop.
I have replaced the master cylinder & power booster. I have bled the lines really good. I checked for air leaks and cant locate any. When I pop off the hose to the power booster it releases the built up air. I hold my finger on the hose and I can feel air sucking from the hose. It doesnt seem to be sucking air as good as what is should.
Any suggestions?
Thanks !

 

[Crumm]

Vacuum pump.

 

[96P_Stroke4x4]

weak vacuum pump x2

 

[95_stroker]

They took my answer.

 

[smokin joe]

That was it. Thanks guys ! ! !

 

[MBRPCrazyford]

OK here's one. My brake work great. The truck stops on a dime. Here's the problem, if I sit with HARD pedal pressure on the brake, it slowly drifts to almost the floor, but not quite. I never lose brake feel or anything like that, they just slowly drift to the floor. Now, when I let off the pedal and get back on it, the pedal is firm just likeit should be and then it starts going towards the floor again. It's weird. The brakes are bled fine, plenty of fluid. Nothing out of the ordinary. I'm not losing brake fluid anywhere. It's a little strange. Any help would be great. thanks

 

[95_stroker]

Hole in the diaphragm in the booster would be my guess.

 

[MBRPCrazyford]

Hole in the diaphragm in the booster would be my guess.

So, that would mean a booster rebuild or a new one? Is there any way I can check the diaphragm? The booster is the big black thing that the master cylinder is attatched to by the firewall, correct?

 

[smokin joe]

They are only like 60 or 70 bucks at Auto Zone.

 

[MBRPCrazyford]

OH, ok, I gotta check into it. Thanks