CDL - Combination Vehicle Practice Test

CDL - Combination Vehicle Practice Test Truck and Trailer Operations 1. **Stopping Distance:** - A fully loaded tractor requires the shortest stopping distance. 2. **Air Leakage Rate:** - The air leakage rate for a combination vehicle with the engine off and brakes on should not exceed **4 psi per minute**. 3. **Importance of Final Air Check:** - Failing to conduct a final air brake check can lead to losing your brakes while driving. 4. **Kingpin Lock:** - The locking jaws of the fifth wheel should close around the **shank** of the kingpin. 5. **Glad Hands Connection:** - Glad hands are used to connect **service and emergency air lines** from the truck to the trailer. 6. **Rollover Risks:** - Trucks are **ten times** more likely to roll over in a crash when fully loaded compared to empty rigs. 7. **Center of Gravity:** - A higher center of gravity makes the truck **easier to turn over**. 8. **Trailer Brake Activation on Breakaway:** - If a trailer breaks away, expect the **tractor protection valve to close**. Coupling and Uncoupling Procedures 1. **Shut-off Valve for Doubles:** - The shut-off valve must be closed in the **back section** of the last trailer. 2. **Fifth Wheel Locking:** - If the fifth wheel locking lever is not locked after closing around the kingpin, the coupling is not right and should be checked. 3. **Inspection Gear:** - After uncoupling the trailer, the tractor engine should be in **neutral**. 4. **Testing Trailer Brakes:** - Apply and release the trailer brakes while listening for sounds to check functionality. 5. **Air Line Connections:** - If the brakes didn't release when the trailer air supply valve was pushed, check the **air line connections**. Emergency Procedures 1. **Major Leak in Service Line:** - A major leak in the service line will cause the **trailer emergency brakes** to activate. 2. **Uncoupling a Trailer:** - After shutting off the trailer air supply, back up gently to ease pressure on the fifth wheel locking jaws. 3. **Using the Hand Valve:** - The hand valve should never be used to park a combination vehicle.