An operator is digging a deep foundation with an excavator and notices that the stick-out force is significantly weaker than normal, causing the machine to struggle. The boom and bucket functions appear to be operating correctly. What is the most likely cause of this isolated issue?

Question: An operator is digging a deep foundation with an excavator and notices that the stick-out force is significantly weaker than normal, causing the machine to struggle. The boom and bucket functions appear to be operating correctly. What is the most likely cause of this isolated issue?

Answer options:

• A main system relief valve malfunction.
• A worn swing bearing. ✅ A faulty stick cylinder seal or a defective stick relief valve.
• Aerated hydraulic fluid in the reservoir.

Correct answer: A faulty stick cylinder seal or a defective stick relief valve.

Explanation: If only the stick-out force is weak while other functions are normal, it points to a problem specific to the stick hydraulic circuit. A faulty stick cylinder seal could allow internal leakage, reducing force, or a defective stick relief valve (if present and set too low or sticking open) would prematurely dump pressure. A main system relief valve issue would affect all functions, a worn swing bearing affects swing, and aerated fluid would cause general sluggishness and noise across multiple functions.