1965 - 1967 Corvette: Chevrolet Service News: Dual Main Cylinder Component Replacement
Source: Chevrolet Service News
Date: August 1967 - Volume 39, Issue Number 9, Part B
The dual main cylinder used on 1967 passenger cars and light trucks is designed and built to satisfy individual brake system displacement requirements for each vehicle line. Therefore, it is necessary that correct parts be used when replacing either complete master cylinder assemblies or the component pistons of these assemblies.
There are two sources for dual main cylinders used on 1967 Chevrolet vehicles: Delco Moraine and Bendix. The Bendix unit can be readily identified by a 'Secondary Piston Stop' bolt on the bottom of the casting. Delco Moraine main cylinders do no have this bolt [reference Figure I, page 5-2 of the 1967 (Passenger Car) Chassis Service Manual].
The displacement capabilities of a particular cylinder are specified by the two letters which are stamped in the metal on the top of the closed end of the master cylinder barrel. Master Cylinders should only be replaced with another cylinder bearing the same two-letter identification.
The length of the secondary pistons in these master cylinders is a critical factor in the displacement capabilities of a particular master cylinder. These secondary pistons are coded, using rings or grooves in the shank or center section of the piston. Refer to the chart below for proper identification.
The primary pistons are of two types. One has a deep socket for the push rod and the other a very shallow socket.
It is mandatory that replacement pistons be identical to the original piston. This can be verified by checking the identification marks on the secondary piston and the socket contour of the push rod end of the primary piston.