When the spring brakes apply automatically as air pressure drops, this typically happens between:
Correct. Spring brakes will fully apply somewhere between 20 and 45 psi as system pressure drops, depending on the vehicle.
CDL Practice Question #125
Category: Air Brakes
Why this question matters
This question is one of 71 in our Air Brakes bank. The reasoning above comes directly from the AAMVA CDL Manual, the source document used by every U.S. state DMV. Memorizing the underlying rule — not just the letter answer — is what separates passing on the first attempt from a return trip and another fee.