[Healeys] troubleshooting rebuilt Girling BJ8 brake servo

[R. Cobb]

Unit was rebuilt using kit from Moss.

Symptoms, following bleeding hydraulic brake system (no differences 
noted whether car running or not): On first try of brakes, nearly no 
braking, with pedal going almost to floor.

Second try, sometimes a release is felt in the pedal (with an 
associated, slight "pop" sound) with a bit more braking and less travel 
of pedal.  By the third try, the pedal travel seems more normal, and the 
braking is improved, though not up to the level expected.

The above pattern has been replicated numerous times, with the thinking 
that perhaps if something were binding, it would work-in. No such luck.

Any thoughts?

I recall that some months ago a contributor mentioned having had to 
install a thinner sponge rubber ring for under the piston seal...because 
of binding(?).  Could this be the issue?  Would this result in the 
behavior I'm experiencing?

Thanks in advance.

Bob