Automobile & Light Truck Certification Test A5 BrakesDrum Brake Diagnosis and RepairMedium
A technician is inspecting the wheel cylinders on a drum brake system. They notice that the rubber boots covering the ends of the wheel cylinders are torn and cracked, but there are no visible signs of brake fluid leakage. What is the MOST important reason to replace these wheel cylinders, even without a current leak?
- ATorn boots indicate the wheel cylinder is old and likely to fail soon anyway.
- BThe torn boots are a cosmetic issue and do not affect brake function until a leak occurs.
- CThe torn boots allow dirt and moisture to enter, leading to internal corrosion and eventual failure.
- DThe torn boots cause a vacuum leak, which affects brake pedal feel.
Show answer & explanationAnswer & explanation
Correct answer: C. The torn boots allow dirt and moisture to enter, leading to internal corrosion and eventual failure.
The rubber boots on a wheel cylinder are crucial for protecting the internal components (pistons, cups, bore) from contaminants like dirt, water, and road salt. Torn or cracked boots allow these elements to enter, leading to corrosion and pitting of the bore, which will inevitably cause leaks and failure.
Why the other options are wrong
- A. While age is a factor, the direct consequence of torn boots is more critical than general age.
- B. This is a safety issue; waiting for a leak is risky and will lead to more extensive repairs.
- D. Wheel cylinders operate hydraulically, not under vacuum, so a vacuum leak is not relevant.
Wheel Cylinder Boot Function
Rubber boots on wheel cylinders protect the internal hydraulic components from dirt, moisture, and debris, preventing corrosion and premature failure.
- Protects internal parts.
- Prevents contaminant entry.
- Cracked boots lead to corrosion.
Memory trick: Boot is torn, cylinder's forlorn, corrosion's born.