A two brake system, one operates the front brakes and one operates the back brakes.
A two braking system, one for each side of the vehicle
A two braking system, one for daytime and one for nighttime driving.
Park on level ground, turn off parking brakes, pull hard on each slack adjuster. It shouldn't move more than one inch.
Park on level ground, turn off parking brake and press brake pedal.
Park on an incline and see if the vehicle rolls.
While the engine is running, step on and off the brake pedal.
Shut off the engine and see if the air pressure leaks down.
Shut off the engine with enough air pressure, turn on the electrical power and step on and off the brake pedal until the low air pressure warning signal comes on.
Step on and off the brake, with the engine off, the parking brake knob should pop out when air pressure falls between 20-40 psi.
Get under the vehicle and pull on the spring brakes.
Turn on the engine and pump the brake pedal down to the floor.
Less than four psi in one minute for single vehicles and less than eight psi in one minute for combination vehicles
Less than two psi in one minute for single vehicles and less than three psi in one minute for combination vehicles
Less than six psi for all vehicles.
Not pressing the brake pedal hard enough.
Over heating, low air pressure, and not relying on the engine braking effect.
Not taking your foot off the accelerator pedal.
So you only have to apply the brake just hard enough to feel a definite slowdown.
So you don't have to shift gears going downhill.
So you can go through the gears on the way down
The brakes could heat up
The brakes could fail.
The brakes could lock up.
So you don't have to drain the air tanks as often.
To have a drink available if you get thirsty.
To reduce the risk of ice in the brake valves and other parts in cold weather.