North Carolina CDL DMV Air Brakes 1
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When a brake pedal is pressed and the S-cam is turned, the S-cam presses the brake shoes against the inside of the brake drum. This causes friction and will cause the vehicle to slow.
Many large CMVs are equipped with air brakes. An air braking system uses compressed air to operate.
In an air brake system, there are three different braking systems: a service brake system, a parking brake system, and an emergency brake system. The emergency brake system uses parts of both the parking and service brake systems.
Pressing and releasing the brake pedal unnecessarily can let air out of the braking system faster than the compressor can replace it. Air brakes may cease to work effectively if the pressure becomes too low.
Tractors, trucks, and buses with Anti-Lock Braking Systems (ABS) have yellow malfunction lamps located on their instrument panels. Trailers have yellow ABS malfunction lamps on their left side, either on the front or rear corner.
It is important to know the maximum air loss rate that is safe for your specific vehicle. A single vehicle with air brakes should have a leakage rate no higher than 3 psi in a minute during an applied leakage test.
Always apply the parking brake when leaving your vehicle unattended.
In an air brake system, there are three different braking systems: a service brake system, a parking brake system, and an emergency brake system. The emergency brake system uses parts of both the parking and service brake systems.
Both systems in a dual air brake system share a single air compressor. If the air compressor is damaged, neither system will be able to operate properly.
Anti-Lock Braking System (ABS) malfunction lamps are usually yellow. Even if the ABS isn't working properly, a driver will still have access to the vehicle's usual braking functions.
The service brake system applies and releases the brakes when a driver presses the brake pedal while driving normally.
On a downgrade, the braking effect of the engine should be your primary method of controlling speed. Shift down to a lower gear before starting down the hill and save the brakes for additional slowing or stopping that may be required by road or traffic conditions.
While driving, spring brakes are generally held in place by air pressure. If the air pressure gets low enough, the springs will activate the brakes.
In vehicles with air brakes, the parking brake is controlled by a knob. The knob is pulled out to apply the brakes, and pushed in to release them.
If a tractor is equipped with an Anti-Lock Braking System (ABS) but the trailer is not, the risk of jackknifing will be reduced and the driver should still be able to maintain steering control. If only the trailer is equipped with ABS, it is less likely that the trailer will swing out to one side.
It is important to know the maximum air loss rate that is safe for your specific vehicle. A triple combination should have a leakage rate no higher than 6 psi in a minute during an applied leakage test.
Water and compressor oil are removed from air storage tanks through a drain valve. The water and oil can damage the brakes if left to accumulate in the system. Manually operated tanks must be drained every day to remove this build-up.
An air compressor governor will stop the compressor from pumping air once the air tanks are at an air pressure level of 125 psi. This air pressure level is referred to as the "cut-out" level.
The most common type of foundation brake is an s-cam drum brake.
Truck tractors with air brakes built on or after March 1, 1997 must be equipped with Anti-Lock Braking Systems (ABS).
The parking brake in a vehicle with air brakes should be used every time the vehicle is parked.
A dual air brake system is made up of two separate air brake systems. The systems share a single set of brake controls, but each has its own air tanks, hoses, and lines.
In an air brake system, pressing and releasing the brake pedal unnecessarily can release air from the braking system faster than the compressor can replace it.
On a long or steep downgrade, brakes should only be used to supplement the braking effect of the engine. Apply the brakes just enough to feel a definite slowing down, then release them once you are about 5 mph below your target "safe" speed. Once your vehicle reaches its safe speed again, repeat this process.
Foundation brakes are used at each wheel. The most common type is the S-cam drum brake.
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