South Carolina CDL Permit Test - Double

Compressed air in an air brake system usually contains a certain amount of water and compressor oil. The water and oil can damage the brakes if left to accumulate in the system. Manually operated air tank drains must be opened daily to remove this build-up.

A driver should inspect wheels before a drive, specifically looking for damage on the wheels and rims. Wheels or rims that have had welding repairs are not safe for use.

When inspecting the convertor dolly, ensure that all components are present and in proper working condition. Be sure to check the upper and lower fifth wheel, the air lines, and the electric lines. The air lines should be securely attached to the proper glad hands and should not contain any leaks. They should be attached with enough slack to allow easy turning.

When backing up to couple a trailer, you should position the tractor directly in front of the trailer. Trying to couple while backing at an angle could cause the trailer to move and the landing gear to break.

When inspecting your vehicle's suspension, verify that leaf springs do not have missing or broken leaves. If at least one-fourth of the leaves in a leaf spring are missing, the vehicle will be put out-of-service until the defect is fixed.

Backing is always dangerous because it is impossible to see everything that is behind your vehicle. Only drive in reverse if it is absolutely necessary.

The most common type of foundation brake is an s-cam drum brake.