Jonn has been looking at the brakes of our 1972 MGB GT, starting with the removal of the cover from the pedal box master cylinder linkage and the brake master cylinder. A new master cylinder was fitted and secured in place, with a new split pin installed in the clevis pin. A pressure bleeder was set up to prime the system before bleeding the front brakes.
The brake bleeding process continued, ensuring the system was fully flushed. After disconnecting the bleeder, initial testing showed some improvement. The engine was started to check the servo operation, which also felt better. The cover was refitted, and the system was set for further testing the following morning.
A pressure check was carried out, and the car was tested around the yard. While the brakes functioned, the pedal travel remained excessive, requiring multiple pumps to firm up. After consulting with Rob, it was suggested to place a washer inside the master cylinder behind the circlip to shorten the piston return stroke. The cover was removed, the washer fitted, and the system reassembled and bled again. However, there was no noticeable improvement.
Upon reviewing the servo installation instructions online, it was discovered that the servo should be mounted at an angle between 25 and 45 degrees from horizontal, differing from its current position. The servo and bracket were removed, repositioned, and marked for drilling. Washers were used to space out the servo before mounting it to the bracket. The mounting plate beneath the servo was ground down for clearance, and the servo was securely refitted with all components tightened. The servo pipe was repositioned, and the bracket was modified to accommodate a long bolt from beneath, securing the servo in place. The system was bled again, and the pedal felt significantly improved. However, the brakes remained engaged once the engine was started.
The pedal cover was removed again, and the process was repeated, but this time the washer was removed from the master cylinder. After reassembly and bleeding, the pedal feel was acceptable, but the brakes still remained engaged upon engine start. Further investigation into the servo vent revealed a missing seal, causing the servo to hold pressure. The old servo was checked, and the missing seal was retrieved and installed. The system was then reassembled and bled once more. After lowering the car off the ramp and conducting a final test, the brakes felt satisfactory, with the pedal travel now within an acceptable range.
