During a routine inspection of a heavy-duty excavator, the operator reports a spongy brake pedal feel. The hydraulic brake fluid reservoir is full, and there are no visible external leaks. Which of the following is the most probable cause of the spongy pedal?

Question: During a routine inspection of a heavy-duty excavator, the operator reports a spongy brake pedal feel. The hydraulic brake fluid reservoir is full, and there are no visible external leaks. Which of the following is the most probable cause of the spongy pedal?

Answer options: ✅ Air trapped in the hydraulic brake system.

• Worn brake pads or linings.
• A seized master cylinder primary cup.
• Contaminated brake fluid.

Correct answer: Air trapped in the hydraulic brake system.

Explanation: Air trapped in the hydraulic brake system is compressible, leading to a spongy or soft brake pedal feel as the air compresses before the hydraulic fluid can effectively actuate the brakes. Worn pads would typically lead to a lower pedal, but not necessarily spongy. A seized master cylinder cup could cause various issues including no brake pressure, but not typically a spongy pedal if the reservoir is full. Contaminated fluid can reduce braking efficiency but doesn't directly cause sponginess.