Brake Master Cylinder: Description and Operation

Exploded View Of Master Cylinder Assembly:

This master cylinder is designed for use in a diagonal split system (one front and one rear brake served by the primary piston, and the opposite front and rear brakes served by the secondary piston).

The tandem master cylinder is similar in construction to an ordinary master cylinder, the principal differences being that it has two pistons and three cups and that hydraulic pressure is developed in two chambers, one for front left & rear right brakes and the other for front right & rear left brakes.

MASTER CYLINDER OPERATION:

Master Cylinder - Normal Operation:

Normal operation:
Depressing the brake pedal forces primary piston "A" toward the left (in Figure) to pressurize the fluid immediately ahead for front left & rear right brakes. By this pressure and by the force of return spring, secondary piston "B" moves similarly to pressurize the fluid for front right & rear left brakes.

Master Cylinder-One Circuit Operation-Front Left & Rear Right Brakes Circuit Failure:

Single circuit operation (front left & rear right brakes circuit failure):
Depressing the brake pedal causes primary piston "A" to move as above but, because the front left & rear right brakes circuit cannot hold pressure, the fluid immediately ahead of this piston does not get pressurized. Piston "A" keeps moving, compressing the spring and when it reaches the piston "B" retainer, it begins to push piston "B". From this point on, piston "B" moves to pressurize the fluid ahead and thus actuate the front right & rear left brakes.

Master Cylinder-One Circuit Operation-Front Right & Rear Left Brakes Circuit Failure:

Single circuit operation (front right & rear left brakes circuit failure):
In this case, the leftward movement of piston "A" has but little effect in pressurizing its fluid (for front left & rear right brakes) at first, because the initial rise in fluid pressure causes piston "B" to promptly yield and move toward the left. Very soon the forward end of piston "B" comes to and bears against the head of the cylinder. From this point on, the leftward movement of piston "A" becomes effective to pressurize the fluid ahead of it for the front left & rear right brakes. The below Figure shows secondary piston "B" at halt.