The most common type of foundation brake found on heavy vehicles is the:
Answer: B
S-cam drum.
S-cam drums are the most common brake design used on foundation brakes for commercial vehicles. There will be one drum per wheel and operated by using an air-activated push rod to rotate an S-shaped cam to move the shoes into contact with the drums.
All choices
- AWedge drum.
- BS-cam drum.
- CDisc.
Why the other answers are wrong
A. Wedge drum.
Choice A is wrong because wedge drum brakes are less common than S-cam drum brakes on heavy vehicles.
C. Disc.
Choice C is wrong because disc brakes are less common as foundation brakes on heavy commercial vehicles compared to S-cam drums.
CDL Air Brakes Test Info
Questions on Exam
25
Passing Score
80%
Time Limit
Typically 30 minutes; varies by testing location
The Air Brakes test content is federally standardized, so this question applies in every state. Age limits, fees, and testing procedures do vary — check your state's CDL requirements.
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More CDL Air Brakes Practice Questions
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- The spring brakes used on the chambers in a straight truck will bring you to a stop when air pressure drops below ____ psi.
- Characteristics of dual air brake systems include:
- Which component of the air brake system cuts-in at 100 psi to allow the air compressor to run?