My 1986 F350 has a brake issue. When I step on the brake pedal it looses it's pressure slowly. There is no leak in the lines, I replaed the brake booster, and the mastercylinder. It has micro? or mac? lock, that I am not familiar with. I bled the brake lines in the front and the rear with the micro/mac? lock on and then when it was off.....What can I do now?

 

Sounds like you got a leaky wheel cylinder in the back end.

Pull the drum and look for signs of fluid inside.

later,
Dustin