Gday,

I think I may know the problem, but want to make sure before I go and buy another master cylinder.

I had spongy brakes in an EF so I put an AU master cylinder in and bled the system. Driving along the pedal just kept getting harder and harder until it got to the point where all 4 brakes were stuck on and the car wouldnt move until I released the pressure from the system.

So Im guessing that the AU master Cylinder must be different to the EF?? Or have I not bled the brakes properly??

Cheers

exactly what my 68XT wagon did after i bled the system, according to the shop i stuffed the booster by pushing the piston too far in ( to hard on the brake pedal when bleeding) brakes stay on cause its not releasing vac or something, so i'd be looking at the booster first

What has happened is that you have pre-loaded the master cyl.
Basically the rod of the booster is holding the master cyls piston in a little, and this prevents it from relieveing pressure. You must either shorten the booster rod or place a suitable sized spacer between the mast cyls body and booster.