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CDL · Brake Fade and Downgrades

What is brake fade, and what causes it?

Reviewed by Jordan Morley, Editorial Lead at 247SimpleTests. Written by the 247SimpleTests Editorial Team from the official source material cited on every question.

Correct answer

Loss of braking effectiveness due to overheated brakes on long descents

  1. A A normal cycle of the air compressor
  2. B The brakes adjusting themselves after high-speed use
  3. C Reduced air pressure on cold mornings
  4. D Loss of braking effectiveness due to overheated brakes on long descents

Why this is the answer

Brake fade is the loss of stopping power that occurs when brakes overheat. Friction between the brake linings and drums or rotors generates heat, and as the brakes get hotter, they lose grip. On a long downgrade where the brakes are applied continuously to control speed, heat builds up faster than it can dissipate, and the brakes progressively lose effectiveness. Eventually they can lose so much grip that the vehicle accelerates uncontrollably even with the brake pedal fully depressed. Prevention: select a low enough gear that engine braking does most of the work on long downgrades, and use the service brakes only intermittently to bleed off speed. The 'snub braking' technique (brake hard to drop 5 mph, then release until speed builds back up, then snub again) keeps brakes cooler than continuous light braking.
Source: FMCSA CDL Manual 5.2.5 Brake Fade

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About this topic: Brake Fade and Downgrades

Brake fade is the loss of braking power that happens when drums or discs get too hot to convert motion into heat efficiently — the pedal still moves, but the truck stops slowing. On the CDL air brakes test it shows up in questions about long downgrades, riding the brakes, snubbing (controlled braking) and why a lower gear, not the service brakes, is your primary speed control on a hill. This is one of 5 Air Brakes questions on brake fade and downgrades, each with a full explanation on a single study page.

New to this exam? Our CDL exam guide explains the format, scoring, and how to prepare.

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