Brake Systems - DELCO-Moraine Dual Piston Master Cylinder: Description

NOTE: All General Motors sub-compact (H and T body styles) models use master cylinders with a common reservoir for both pistons. All other makes and models use master cylinders with two reservoirs, one for each piston.

Master cylinder is a single cylinder with front and rear pistons. Unit can have a divided reservoir or a common reservoir. Rear piston is operated by a pushrod. Front piston is operated by rear piston. In a separated reservoir, the larger reservoir feeds the disc brakes. This is because the pistons used on disc brakes are larger than wheel cylinders used on drum brakes. A residual pressure valve is located in the master cylinder under outlet seat for drum brakes. This keeps a small amount of pressure in drum brake circuit. Disc brake outlet does not have a residual pressure valve.

NOTE: Disc brakes must not have any residual pressure or they will lock up.

On some master cylinders a stop screw is screwed in from outside of cylinder. This stop screw limits return stroke of front piston. Some master cylinders have one outlet on bottom and one on the side. A bleeder screw on these master cylinders allows trapped air to be released.

NOTE: Chrysler models do not use a residual valve for rear drum brakes.