Air brake problem bedford bus 1977

[damotron666]

Hi guys newbie
I have a 1977 bedford bus pek1bfw
Has air assisted brakes all of a sudden the air pressure only builds 20psi and stays at that in normally goes to 7bar 100psi 90 seconds but now it will only build to 20psi and it holds 20psi so no leaks wondering what could this be i had to pump compressor up with a portable compressor but after a while of driving the air goes back down to 20psi and the brakes wont release.
Any help would be much appreciated.

[RustRemoverJim]

Did you find the problem? I’ve got similar issues, I have replaced a broken spring on the compressor delivery valve but not cured it. Compressor head coming off next. Any tips welcome.

[RustRemoverJim]

To get the head off with the compressor still fitted to the engine, the head fouls the exhaust manifold way before it clears the studs. Manual says remove the manifold. On mine that would also need to remove one of the injector pipes. I managed to avoid doing this by removing the 3 long head studs by removing the washers and locking 2 head bolts on to the studs, they cracked off easily.