Jaguar Repair: 1985 series 3 4.2, master cylinder, series 3

Question
Hi, Brakes work fine when stopping at lights etc but,I lose the pedal pressure when waiting for green light. I am not losing any fluid that I can see.After pumping for 1 or 2 times the pressure is back up again. Someone said it could be Servo problem ?????? Can you help  Pleeeeeeeze.

Answer
Hi David,
The symptom you out line is of a bad master cylinder. (If you are not loosing fluid)
Sometimes it is noted that light pedal pressure seems to go to the floor faster than hard pedal pressure at a stop light.
The fluid is bypassing the master cylinder piston, that is why no fluid is lost.
Howard