1. Measure the depth of the recess in the back of the MC piston with the butt end of a dial caliper.

2. Cut a strip of light cardboard the same width.

3. Use this cardboard strip as a gauge to adjust the length of the booster push-rod.

In other words, the distance from the face of the booster to the tip of the push-rod must equal the depth of the recess in the MC piston.