If you are driving a vehicle with air brakes, you should check the slack adjusters.

True, they should not move more than 1 inch when pulled by hand (with brakes released).. Section 5.3: Check slack adjusters. If they move

If you are driving a vehicle with air brakes, you should check the slack adjusters.

ANSWER BREAKDOWN
  • A. Correct. Check slack adjusters. If they move more than about one inch where the push rod attaches, they need adjustment.
  • B. Incorrect. "False, mechanics check them." is not correct. Check slack adjusters. If they move more than about one inch where the push rod attaches, they need adjustment.
  • C. Incorrect. "Only if the brakes fail." is not correct. Check slack adjusters. If they move more than about one inch where the push rod attaches, they need adjustment.
  • D. Incorrect. The required depth is 1 inch, not 3 inch. Check slack adjusters. If they move more than about one inch where the push rod attaches, they need adjustment.