South Carolina CDL Permit Test - Air Brakes

Brakes are particularly prone to getting out of adjustment if they are hot. Be sure to routinely check the adjustment of your brakes. For a vehicle to be safely controlled, all brakes must be properly functioning and adjusted.

While driving downhill, you should hold down the brake pedal until your vehicle reaches a speed 5 mph below your safe speed, then release the brake pedal. Repeat this process.

Some pre-1975 vehicles have a front brake limiting valve, which has "normal" and "slippery" settings. The idea behind these valves was to limit the air pressure available to the front brakes when driving on slippery surfaces, and thereby reduce the danger of a front-wheel skid. Studies have found that this is not actually a concern, so if your vehicle has a front brake limiting valve, leave it in the "normal" position.

Foundation brakes are used at each wheel. The most common type is the S-cam drum brake.

Always apply the parking brake when leaving your vehicle unattended.

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.