Just seen this on the Merlin Motorsport website...........
THE LEARNING CURVE
This problem came from a very competent builder of specialised 4X4 vehicles. He was using Girling master cylinders. The problem was that after applying the brakes one circuit retained the pressure and would not release. Opening the bleed valve released the pressure; the brakes could then be applied but would again not release the pressure. We had seen this problem before. It is caused when the brake pedal hits a stop and does not allow the push rod to retract fully. This means that the piston in the master cylinder does not uncover the port and allow the pressure in the system to release. The solution is to make sure that when the pedal is released there is a small amount of play in the push rod.
The customer was adamant that the pedal was releasing fully but still the brakes would not release. He returned a week later to explain what had happened. The analysis was correct but for a different reason. He had changed the push rod and when replacing the washer and circlip he had fitted the washer the wrong way round. The washer is about 3mm thick with a chamfer on one side to accommodate the ball on the pushrod. The chamfer should be on the inside which allows the ball to fit in the chamfer. The other way round stops the piston from retracting fully.
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