Triumph Repair: 1973 TR6 Brake problems, disc brakes, brake servo

Question
Have replaced entire brake system except hard lines and servo unit. After about 8 miles of travel - front disc brakes lock up and overheat, the brake pedal gets very hard while traveling. can this be caused by the brake servo unit? If not - what else could be the cause? I am using castrol LMA brake fluid.

Answer
Hi Chuck,
For the brakes to lock up and the pedal to feel hard the master cylinder piston is held down. When you release the pedal the master cylinder piston MUST return to a point that there is an open and free channel of fluid from all four wheels to the reservoir. The fact that the pedal is hard proves this is not the case on your car. First confirm that the pedal returns fully. Then do this, run the car until the brakes are in a bind and quickly jack up the front and loosen a bleeder valve to see if the wheel gets free. If so and the brake pedal does return do it again and this time loosen the two nuts mounting the master cylinder to the booster. If it lets the wheels free you have a problem between the master and the booster. Some had an adjuster in between but if not you may have to make a thick gasket to space the master cylinder away from the booster a little.
Howard