Originally Posted by Jimz Bird
... That is opposite some of the TBirds (all 55-57) and some of the Square Birds (Under dash booster I think - need others input on that) which have the booster after the MC.
Squarebirds that have the Kelsey-Hayes booster have a tab on the brake pedal arm that presses on switch on the K-H booster that opens a valve and uses vacuum to pull on the brake pedal arm - power assist. The pushrod goes from the brake pedal arm to the MC. The K-H unit is off to the side. The MC for K-H power brake system has a 1-1/16" bore rather than a 1" bore for non-power brakes thereby requiring less travel but more pressure on the brake pedal, which is more than overcome by the power assist.