Automobile & Light Truck Certification Test A5 BrakesDrum Brake Diagnosis and RepairMedium
When replacing drum brake shoes, technician A states that the primary shoe is typically shorter than the secondary shoe and faces the front of the vehicle. Technician B states that the primary shoe has less lining material and is positioned towards the front of the vehicle. Who is correct?
- ANeither Technician A nor Technician B
- BTechnician A only
- CTechnician B only
- DBoth Technician A and Technician B
Show answer & explanationAnswer & explanation
Correct answer: C. Technician B only
The primary shoe (leading shoe) is indeed positioned towards the front of the vehicle and typically has less lining material than the secondary shoe. Its main function is to initiate contact with the drum, which then 'energizes' the secondary shoe through self-energization. Technician A is incorrect about the shoe length.
Why the other options are wrong
- A. Technician B made a correct statement.
- B. Technician A is incorrect about the primary shoe being shorter; it's the lining material length that differs.
- D. Only Technician B's statement is accurate regarding primary shoe characteristics.
Primary vs. Secondary Brake Shoes
Drum brake shoes are differentiated by their position and lining material, affecting their role in the self-energizing braking action.
- Primary shoe: faces forward, less lining, initiates contact.
- Secondary shoe: faces rearward, more lining, provides main braking force due to self-energization.
- Self-energization: rotation of the drum pulls primary shoe into drum, which then pushes secondary shoe harder.
Memory trick: Primary leads the way, secondary does the heavy work, always remember the lining play.