Home › CDL Practice Tests › General Knowledge Questions › Question 140
What must you do with the trailer air supply before stepping out to uncouple on a grade or soft ground?
- A.Turn off all cab power
- B.Disconnect the glad hands first
- C.Leave the trailer brakes released so it can roll freely
- D.Set the trailer spring brakes by pulling the trailer air supply control, and chock the wheels if conditions call for it
Correct answer
D. Set the trailer spring brakes by pulling the trailer air supply control, and chock the wheels if conditions call for it
Why
Spring brakes set and, where needed, chocks keep the trailer exactly where you left it while the tractor is detached. Releasing air first also confirms the spring brakes actually apply before you trust them to hold the trailer alone.
Manual topic: Combination Vehicles - Uncoupling · From the General Knowledge practice bank (GK-140).