I was driving when i put the brakes on the pedal went to the floor. I pumped the pedal a couple of times to get brakes. I checked the front disc brake pads and they look almost new, i replaced them a few months ago. I checked the rear brakes and they are worn down probably 3/4 of the way. I checked for leaks at the wheel cylinders and found no leaking in the front or the rear. I did find the rear adjusters were not working so the rear brakes were not adjusting out as they wear. I manually adjusted them out so there would not be so much shoe travel before they hit the drum. Didn't help. I replaced the master clylinder and bled the brakes, the pedal was good untill i started the engine at that point the pedal went to the floor. I checked the vacum hose to the booster and had good vacum. I then replaced the vacum booster unit and when i pushed on the brake pedal i had good pedal until i started the engine and it went to the floor. I rebled the brakes, used over a pint of fluid. I made sure that i had good flow with no air bubbles. Still very little pedal when the engine is running.
Someone told me that i had to make sure the master cylinder is for drum brakes in the front and disc brakes in the rear.I don't know what the difference is but when i ask about this from the local auto parts store they did not know what i was talking about. The book listed the one they sold me.
I'm thinking about replacing the wheel cylinders on the rear and the front calipers, the only thing left would be the brake lines.
Does anyone know what i'm doing wrong? Any help would be appreciated.
John Spangler

 

You didn't mention anywhere in your thread that you bench bled the new/rebuilt master cylinder.

 

I forgot to mention, yes i did bench bleed the new master cylinder.

 

Did you bleed the Load Sensing Proportional Valve (lspv) that is mounted to the right inside frame? It is the rod that is connected to the rear axle.
That leaks sometimes