Which of the following elements does not belong to disc air brakes?
- Rotors
- Brake pads
- Return springs ✓
- Calipers
Answer: C. Return springs
Return springs are not part of the disc air brake components listed; rotors, calipers and brake pads are.
Why this is the answer
The handbook lists disc air brake components as rotors, calipers, brake pads, slack adjusters and brake chambers. Return springs appear in the list for "S" cam air brakes, where they pull the brake shoes back to the released position. A return spring is also described inside a service brake chamber, but it is not one of the foundation disc brake parts. So when the question asks what does not belong to disc air brakes, the return spring is the item that fits the "S" cam hardware list, not the disc list.
Why the other answers are wrong
- A. Rotors — Rotors are listed as disc air brake components and are the disc surface the pads clamp against.
- B. Brake pads — Brake pads are part of disc air brakes and press against the rotor to create braking force.
- D. Calipers — Calipers are part of disc air brakes and hold the brake pads.
Remember it
Picture a disc brake as rotor, caliper and pads; the return spring is tied to the "S" cam drum hardware list.
Official handbook: Official MTO Air Brake Handbook, Foundation Brakes – Key points to remember