ok so whats going on before we changed some parts is brakes work then loose pedal but then comes back. i checked everything that deals with the brakes. vaccum hose to the booster looks good and is connected. master cylinder was not leaking in to the booster. no leaks anywhere from the calibers or drums. we have changed out the calibers and master cylinder, bleed the brakes. its still has the same problem. what do you think it could be....

 

I know you checked the booster.... But... Maybe it's still the problem..?

Edit- ya got abs?

 

if the booster was bad it would be just a hard brake. this is my buddys XJ im helping out on, and remembered that he ran his intake/filter over by the vaccum pump. where all the hoses connect to and i had him go check it maybe somthing broke or came a little loose from the mod. everytime he shuts the hood it pushes down on his filter then in the the pump house. i asked him if the problem started after he did that and he said yes, so im thinking thats the problem.

 

The master cylinder can be leaking internally. Check the rear brake adjustment before replacing the master cylinder, the shoes should just barely contact the drum if adjusted correctly.

 

that the first thing i did for it. i did everything you can do to the brakes before replace things. ive already replaced the master cylinder and both fron calibers. the bleeders screws broke so had to replace them. but yea rear drum i where they should be.