After replacing brake pads on a hydraulic brake system of a heavy-duty wheel loader, the technician attempts to bleed the brakes. Air continues to be expelled from the bleeder valve despite repeated attempts, and the brake pedal remains soft. What is the most likely reason for this ongoing issue?

Question: After replacing brake pads on a hydraulic brake system of a heavy-duty wheel loader, the technician attempts to bleed the brakes. Air continues to be expelled from the bleeder valve despite repeated attempts, and the brake pedal remains soft. What is the most likely reason for this ongoing issue?

Answer options:

• The master cylinder is bypassing internally.
• The caliper bleeder valve is not sealing correctly.
• Air is entering the system through a worn wheel cylinder seal. ✅ The brake fluid reservoir is being allowed to run dry during bleeding.

Correct answer: The brake fluid reservoir is being allowed to run dry during bleeding.

Explanation: If the brake fluid reservoir is allowed to run dry during the bleeding process, air will be introduced into the master cylinder and the rest of the system each time, making it impossible to achieve a firm pedal and continuously expelling air. While other issues like internal master cylinder bypass or worn seals could cause braking problems, running the reservoir dry is a common error during bleeding that directly leads to the described symptoms.