Automobile & Light Truck Certification Test A5 BrakesDrum Brake Diagnosis and RepairHard
A technician is replacing drum brake shoes. They notice that the wheel cylinder bores are slightly pitted but not leaking. Technician A states that the wheel cylinder should be replaced. Technician B states that the wheel cylinder can be honed to remove the pitting, provided the bore isn't excessively oversized. Who is correct?
- ATechnician B only
- BNeither Technician A nor Technician B
- CBoth Technician A and Technician B
- DTechnician A only
Show answer & explanationAnswer & explanation
Correct answer: D. Technician A only
Pitting in a wheel cylinder bore, even without current leaks, compromises the sealing surface for the rubber cups. Honing can sometimes remove very minor corrosion, but pitting often requires removal of too much material, leading to an oversized bore or insufficient sealing. Best practice is to replace pitted wheel cylinders to ensure reliability and safety.
Why the other options are wrong
- A. Honing can remove minor surface rust, but pitting usually requires too much material removal, compromising the bore.
- B. Technician A is correct; replacement is the standard and safest procedure for pitted wheel cylinders.
- C. Honing is generally not recommended for pitted bores due to safety and performance concerns.
Pitted Wheel Cylinder Bores
Pitting in a wheel cylinder bore is corrosion that creates small depressions, compromising the sealing surface for the rubber cups and leading to potential fluid leaks.
- Compromises seal integrity.
- Can lead to brake fluid leaks.
- Replacement is generally recommended.
Memory trick: Pits in the bore, safety's no more, replace it, for sure.