South Carolina CDL DMV Endorsement Double 2

Because air pressure can eventually leak away, the emergency brakes in an air brake system must be held on by mechanical force.

Most heavy vehicles with manual transmissions require double clutching to shift gears. Learning to effectively change gears by double clutching takes practice.

Older trailers do not have spring brakes. This means that if the air supply in an older trailer's air tank has leaked away, there will be no working brakes connected to the trailer and its wheels will turn freely.

When coupling air brake hoses, you should make sure the proper pairs of gland hands are connected. They are sometimes color-coded to help drivers avoid mistakes. Typically, blue is used for service lines and red is used for emergency lines.

Because they are exposed to less sunlight and warm up more slowly, shaded areas will remain icy and slippery after ice on other areas of the road has melted.

If you need to make an emergency stop, you can use either the controlled braking method or the stab braking method. It's important to brake in a way that keeps your vehicle in a straight line but will still allow you to turn if necessary.

There are two indicators that determine when you need to shift into a higher gear. One indicator is the engine speed (rpm). You should read your vehicle's manual to learn its rpm range and shift up when you reach the top of that range. The other indicator is road speed (mph). You should learn which speeds each gear can accommodate, then keep an eye on the speedometer and shift up as needed.

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. Tanks must be drained regularly to remove this build-up.

Retarders are mechanisms in some vehicles that help slow a vehicle and reduce the need for braking. The four basic types of retarders are exhaust, engine, hydraulic, and electric.

The suspension system keeps a vehicle's axles in place. Damaged suspension parts, such as leaking shock absorbers, may be potentially dangerous defects on a vehicle.

If you must drive in fog, be sure to slow down. Turn on your flashers and low beam headlights.

Components of an air brake system include an air compressor, an air compressor governor, air storage tanks, air tank drains, an alcohol evaporator, a safety valve, a brake pedal, foundation brakes, supply pressure gauges, an application pressure gauge, a low air pressure warning signal, a stop light switch, a front brake limiting valve (on some older vehicles), spring brakes, and parking brake controls.

Due to their size, doubles and triples cannot be turned suddenly. They require extra care to avoid rollovers when turning.

For safe driving, it is essential that you maintain cushions of space on all sides of your vehicle. This helps to ensure that you will have time to take appropriate action if a problem arises.

It is essential to safety that a driver inspects coupling before starting a trip. Trailer coupling on a double or triple combination can be tested by pulling against the pin of the second semi-trailer.

Rollovers can happen when a combination vehicle is turned too quickly. To help prevent the risk of rollover, it is important to keep the vehicle's center of gravity low by loading cargo as close to the ground as possible.

All commercial motor vehicles are required to be equipped with the proper emergency equipment. This may include spare electrical fuses; three red reflective triangles, six fuses, or three liquid burning flares; and at least one properly charged and rated fire extinguisher.

Brakes out of adjustment will fade before those that are properly adjusted. Brake adjustment must be checked frequently to help prevent brake issues.

Because doubles and triples are more vulnerable than singles to jackknifing and rolling over, drivers should look far ahead of their vehicles so they can react to hazards well in advance and slow down or change lanes gradually.

In an air brake system, the air tanks are equipped with drains that allow water and compressor oil to be removed from the system. If allowed to build up, water and compressor oil can damage an air brake system.