Heavy, slow boom: causes of weak hydraulics on excavators and backhoes

Weak hydraulics show up as slow movement, a boom that won't lift the load, or a bucket that won't curl with force. The hydraulic pump is expensive, so don't start there. Most cases have a simpler cause.

Most common causes

• Low hydraulic oil level.
• A clogged hydraulic filter (return or suction).
• Very hot hydraulic oil: it thins out and pressure drops, especially in summer.
• Old oil, water in the oil, or the wrong oil grade.
• Air in the system after a hose change or after running low on oil.
• A faulty or wrongly set relief valve.
• Internal wear in the pump or cylinder seals (the last possibility).

Checks

1. Lower the boom to the ground and check the hydraulic tank level as described in the manual.
2. Look at the oil colour: milky means water; very dark with a burnt smell means old or overheated oil.
3. Check when the hydraulic filter was last changed, and replace it if overdue.
4. Check that the oil cooler is clean. Dust on it raises oil temperature.
5. Is the weakness in every function or just one? All functions = usually oil, filter or pump. One function = usually that function's cylinder or valve.
6. If everything checks out, a pressure test with a gauge by a technician will show whether the pump or the valves are at fault.

Summary

Oil, filter and temperature are the first three things to check. A hydraulic filter changed on time protects a pump that costs many times more.