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Question

Difficulty: EasyBraking Systems

A technician and an assistant are performing a standard two-person manual brake bleeding procedure to purge trapped air from a vehicle's hydraulic brake lines. In what chronological sequence should the steps of a single bleeding cycle be performed?

  1. 1Depress and hold the brake pedal down firmly to pressurize the hydraulic circuit.
  2. 2Open the bleeder screw slightly to allow aerated brake fluid to discharge into a catch container.
  3. 3Close and tighten the bleeder screw securely.
  4. 4Release the brake pedal slowly back to its resting position.

Answer

The correct sequence begins with depressing and holding the brake pedal, followed by opening the bleeder screw to vent air, tightening the bleeder screw, and finally releasing the brake pedal.
During a two-person manual brake bleed, the system must first be pressurized by depressing and holding the brake pedal. Opening the bleeder screw then allows trapped air bubbles and fluid to escape under pressure. Closing the bleeder screw before releasing the pedal ensures that atmospheric air is not drawn back into the hydraulic system when the master cylinder piston returns.

Step-by-Step Solution

1
Instruct the assistant to depress and hold down the brake pedal.
Hydraulic pressure builds within the master cylinder and brake lines.
Pressure is required to push fluid and trapped air out of the open valve.
2
Loosen the bleeder screw on the caliper or wheel cylinder roughly a quarter to half turn.
Air bubbles and fluid escape through the bleeder port into the tubing/container.
The differential between hydraulic line pressure and atmospheric pressure expels the air.
3
Tighten and close the bleeder screw before signaling the assistant.
The hydraulic system is sealed against atmospheric air entry.
Prevents air from being drawn into the caliper or cylinder when the pedal returns.
4
Signal the assistant to release the brake pedal.
The master cylinder piston returns, drawing fresh fluid from the reservoir into the bore.
Completes the bleeding cycle and prepares the system for the next stroke.

Key Concept

Manual Hydraulic Brake Bleeding Procedure
Estimated Time:45s
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Topics

Braking Systems

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