I have a SC430 that is fitted with a LS430 master cylinder and vacuum servo
( The ABS bits were all removed)



After bleeding the pedal is rock solid.
Problem with engine started........the pedal goes to the floor and seems soft

Have bled it several times with no improvement when the engine is running.

Brake lines have been T'd front and back to each master cylinder ports

I originally tried a smaller Toyota Celica servo with a jaguar Series3 master cylinder
Same problem......firm pedal with engine off and then soft to the floor with engine running.



2 different servos with master cylinders giving the same issues.
Firm pedal when engine off - then to the floor and soft with engine running.

Any ideas ?