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NM CDL Air Brakes study materials
NM CDL Air Brakes study resources

NM CDL Air Brakes: Using Air Brakes Safely: Stopping, Parking, and Braking Technique

NM CDL Air Brakes · Work through your exam, one topic at a time.

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Using Air Brakes Safely: Stopping, Parking, and Braking Technique

This domain tests stopping distance, controlled and stab braking, downgrade technique, parking on grades, and ABS use. The exam wants practical judgment, not just component names.

Core rules

  • Air brakes do not shorten stopping distance. Weight, speed, brake condition, and road surface determine it. Expect some lag between pedal movement and brake force.
  • Controlled braking: press steadily and firmly without locking the wheels, and hold enough pressure to slow or stop while keeping steering control. Do not pump the pedal.
  • Stab braking: push the pedal fully, release when wheels lock, and reapply as soon as they roll. Use it only when necessary and understand its limits; with ABS, brake normally and do not pump.
  • On a downgrade, select a low enough gear before starting down. Use snub braking: brake firmly to reduce speed, release, let speed build slightly, and repeat. Do not ride the brakes.
  • Parking: set the parking brake, place the transmission in a low gear or park, and chock wheels when needed. Turn wheels toward the curb or shoulder when facing downhill, and away from the curb when facing uphill with a curb. Do not use the trailer hand valve for parking.
  • ABS is an add-on. A yellow ABS lamp that stays on means ABS is not working, but normal brakes remain. Brake normally.

Worked example

A loaded tractor-trailer starts down a 6% grade at 55 mph. The driver selects a gear that holds about 45 mph, brakes firmly to 35 mph, releases, and lets speed build back to 45 mph before repeating. Reasoning: snubbing gives the drums time to cool. Riding the brakes would overheat them, cause fade, and increase stopping distance.

Traps that cost marks

Do not fan the brakes or use the parking brake to control speed. Do not coast in neutral on a grade. Do not assume ABS always shortens stopping distance. Do not use the trailer hand valve as a parking brake.

Key points

  • Air brakes do not reduce stopping distance.
  • Controlled braking is steady; do not pump.
  • Snub braking on grades; use a low gear.
  • Park with the parking brake, chocks, and proper wheel direction.
  • ABS lamp on: normal brakes still work; brake normally.