Which of the following is an advantage of wedge brakes over S-cam drum brakes?
- No exposed linkage ✓
- Simpler design
- More braking power
- Installed on more commercial vehicles
Answer: A. No exposed linkage
The advantage is that wedge brakes have no exposed linkage.
Why this is the answer
The handbook describes wedge air brakes as drum brakes with brake drums and shoes and no exposed brake linkage. The brake chambers sit with pushrods facing inward, and the pushrod stroke slides a wedge between the shoes to press them outward. By contrast, the S-cam brake description notes an exposed pushrod as a characteristic of that design. So when you compare the two, the wedge layout keeps the linkage out of view, which is the advantage named in the question.
Why the other answers are wrong
- B. Simpler design — The passages list wedge components but do not say wedge brakes are simpler; the named advantage is the absence of exposed linkage.
- C. More braking power — No passage compares braking power between wedge and S-cam brakes, so more braking power is not given as an advantage.
- D. Installed on more commercial vehicles — The handbook says the S-cam brake is the most common foundation brake on commercial vehicles with air brakes, so wedge brakes are not described as more widely installed.
Remember it
Remember the wedge hides its linkage; the S-cam is the one with the exposed pushrod.
Official handbook: Official MTO Air Brake Handbook, Foundation Brakes – Wedge brakes