[169indy]

I like to study the Section 5 Brakes of any GM Chev Chassis Service Manual.

Definitions from them: 1968

A) <<SWITCH>> A New brake pipe distribution and switch assembly is mounted below the main cylinder. Front and rear hydraulic brake lines are routed from the main cylinder, through the brake pipe distribution and switch assembly, to the front and rear brakes. The switch is wired electrically to the brake alarm indicator light in the instrument panel. If a leak in either front or rear system occurs, the pressure differential (150-250 psi) during brake application will cause the piston to compress the springs and move (the piston) in the bore until it touches the electrical contact (grounding the circuit) which causes the parking alarm brake lamp on the instrument panel to light.

B)<Lower Rears><PRESSURE REGULATOR VALVE>> On certain models the rear brake hydraulic line is routed through a pressure regulator valve mounted on the left subframe rail. The valve controls the hydraulic pressure to the rear brakes resulting in the correct pressure balance between the front and rear hydraulic systems.

C)<Upper Fronts-DISC BRAKE Car>< PRESSURE REGULATOR VALVE>>Models with disc brakes have a pressure regulator valve mounted below the main cylinder. The valve meters the hydraulic pressure to the front brakes resulting in simultaneous braking balance between the front and rear brake systems. This valve guards against premature lock-up of the front wheels when the brakes are applied.

I know my 69 Pace car stops very nice and maintaining a correct bleed and brake system maintenance should be considered one of any enthusiast first priorities. Going FAST is easy, Stopping is Critical.
Try stopping a 1925 Hudson super 6 at 35mph, external friction OD brakes on the REAR only, You have heard of ARMSTRONG steering, try one step above Fred Flinstone BRAKES

Jim W