Manitou MLT 737 Steering Heavy and Slow at Idle
Fault Codes & Symptoms
Steering is very heavy and slow at low engine RPM. Steering effort and speed improve with higher engine RPM. Related symptoms: - Slow hydraulic functions at low idle. - Delayed hydraulic response. The machine is difficult and slow to steer in the yard unless I rev the engine up, then it seems fine. It used to be easy to steer at an idle.
Confirmed cause: The load sense priority valve spool was sticking due to contamination. The spool was not shifting correctly at low flow (low idle) to direct the load sense signal to the pump controller. Repair performed: Removed the steering priority valve assembly. Disassembled the valve on a clean bench and found the main spool was contaminated with fine debris, causing it to bind in the bore. Cleaned the spool and valve body with solvent, lightly polished the spool to remove minor scoring, and reassembled with new seals. Verification: After re-installing the priority valve, the machine was started. Steering was responsive and light at low idle. The load sense signal at the pump now showed a clear increase when the steering wheel was turned at any engine RPM. Technician notes: - This issue can be intermittent depending on oil temperature. - The contamination found in the valve suggests a larger hydraulic system health issue. Recommend taking a hydraulic oil sample for analysis. - Always cap hoses and fittings immediately during disassembly to prevent further contamination.