Automobile & Light Truck Certification Test A5 BrakesHydraulic System Diagnosis and RepairEasy
A technician is preparing to install a new master cylinder. Before installation, they are performing a 'bench bleed' procedure. What is the PRIMARY purpose of bench bleeding the master cylinder?
- ATo pre-fill the master cylinder reservoir with fluid.
- BTo verify the master cylinder's internal seals are intact.
- CTo remove all air from the master cylinder's internal chambers.
- DTo ensure the brake fluid is compatible with the system.
Show answer & explanationAnswer & explanation
Correct answer: C. To remove all air from the master cylinder's internal chambers.
Bench bleeding is crucial for removing all air from the master cylinder's internal chambers before it's installed on the vehicle. This prevents air from entering the rest of the brake system, which would cause a spongy pedal and require extensive bleeding later.
Why the other options are wrong
- A. While the reservoir is filled, the purpose is to cycle fluid through the internal passages to expel air, not just to fill it.
- B. While a leak might be detected, the primary purpose is not seal verification.
- D. Fluid compatibility is determined by type, not by bench bleeding.
Master Cylinder Bench Bleed
Bench bleeding a master cylinder involves filling it with fluid and cycling its pistons to expel all internal air before installation, preventing air from entering the vehicle's brake lines.
- Performed off the vehicle.
- Uses short lines or plugs to recirculate fluid.
- Removes trapped air from piston bores and ports.
- Prevents a spongy pedal after installation.
Memory trick: Bench bleed: get the air out before it's a vehicle's headache.