Prior to 1967, most automotive master cylinders were limited to just one hydraulic reservoir and this reservoir was the only one which distributed hydraulic fluid to each wheel.
Step on the brakes and the brakes worked. The single hydraulic reservoir limited the system to either working, or not.
There were several companies which worked on a dual-cylinder brake system. Wagner Electric, later acquired by Studebaker, developed a dual- cylinder brake system.
The dual-cylinder brake system made it safer to drive a car which had a dual-brake brake system.
And in 1962, Cadillac developed a system that used a dual-braking system with separate front and rear hydraulic lines so that if one circuit had a leak, the other could still stop the car.
American Motors also offered the tandem(split) cylinder system as standard equipment. The split diagonal system divided the brake circuits between one front wheel and one rear wheel on opposite sides of the vehicle. It was not a complete front to rear system but it was a step in the right direction.
Dual master cylinders have two separate chambers that separate the front and rear brake circuits. This type of system prevents the total loss of braking action in the event of brake fluid loss. The brake circuits can be split front and back or diagonally.
Both systems will stop the vehicle with only one circuit operating, however, this system is not safe for normal use, but there would sufficient fluid left in the system to allow safe stoppage of the vehicle.
Operation of the dual master cylinder is simple. When the brake pedal is depressed, force is applied through the push-rod to the master cylinder piston.
As the piston cup is forced forward, brake fluid is trapped and hydraulic pressure builds. Hydraulic pressure causes the movement of brake assemblies, such as calipers or wheel cylinders, to stop the rotation of the wheels.
When the brake pedal is released, fluid is forced back through the lines into the master cylinder reservoir.
Vehicles that have disc brakes in the front and drum brakes at the rear require a metering valve (see below). Disc brakes are always in contact with the rotor, but with the drum brakes, they are slightly pulled away from the drums.
Symptoms of master cylinder failure
Like all other automotive systems, the most common cause of master cylinder failure can be attributed to:
- Normal wear
- Contamination, as the brake fluid is hygroscopic (attracts water)
- External corrosion
What is a power brake booser?
The first power brake booster was invented in 1927 by Belgian engineer Albert Dewandre. By 1928, Pierce-Arrow was the first car company that used a power booster system.
Although vacuum brake boosters were available from that point on, they didn’t become standard equipment until much later.
Drum brake systems took less power to operate but the advent of the disc brake, made it necessary to use a power brake system.
Power disc brake systems are difficult to operate because it takes a lot of force to depress the pedal, which was complicated by the fact that the average passenger car used to be a lot bigger and heavier than the average car that’s on the road today.
What is a metering valve?
Vehicles that have disc brakes in the front and drum brakes at the rear require a metering valve. Disc brakes are always in contact with the rotor, but with the drum brakes, they are slightly pulled away from the drums.
The metering valve allows the drum brakes to come in contract just before the disc, until a threshold pressure has been reached.
This threshold pressure is very low and just barely engages before the disc brakes kick in.
By having the rear drum brakes engage before the front brakes disc brakes gives the vehicle more stability and keeps the vehicle in a straight like.
What is a pressure differential switch?
The pressure differential valve is a piston switch that lets the driver know if a leak occurs in one of the brake circuits. As long as the pressure in both circuits is the same, the piston will stay centered in its cylinder. But if one side develops a leak, the pressure will drop in that circuit, forcing the piston off-center.
This closes a switch, which turns on a dash warning light in the instrument panel of the car.
What is a proportioning valve?
The proportioning valve reduces the pressure to the rear brakes- regardless of what type of brakes a car has, because the rear brakes require less force than the front brakes.
The amount of brake force that can be applied to a wheel without locking it depends on the amount of weight is on the wheel.