Howo Mining Truck Slow Lift, Weak & Jumpy Lift Fault Solution

Slow lifting, insufficient power and obvious jerking/shaking during the cargo box lifting are frequent hydraulic faults on mining dump trucks. The main causes include air entering the hydraulic system, insufficient oil pressure, blocked oil lines, internal leakage, stuck valve bodies and excessive mechanical resistance.This malfunction shows mild abnormalities when unladen and worsened weakness and jerking under heavy load. Continuous operation with this fault will accelerate wear of the hydraulic pump and oil cylinder, and may lead to stuck lifting or spontaneous box dropping. Below is a step-by-step troubleshooting guide from simple to complex, for all Howo mining truck models.

I. Quick Preliminary Inspection (No disassembly required, 5-minute check, prioritize this)

1. Check Overloading and Working Conditions

Overloaded materials, vehicle parking on slopes or uneven cargo load will overload the lifting system, resulting in slow lifting and jerking from uneven force.Solution: Remove excess materials, park the vehicle on flat ground and test lifting with empty box. If the performance returns to normal under no load, the problem is caused by overloading; follow loading specifications.

2. Check Hydraulic Oil Level and Oil Condition

Low hydraulic oil level causes pump cavitation and air ingress into the system, which is the most common cause of jerking. Deteriorated, emulsified or contaminated oil leads to poor oil supply and unstable pressure.Inspection: Shut down the engine and wait for 5 minutes. Check if the oil level is within the marked range on the tank. Top up with OEM hydraulic oil of the same grade if insufficient. If oil is foamy, cloudy or emulsified, replace hydraulic oil and clean the oil tank.

3. Inspect External Oil Leakage and Deformed Pipelines

Focus on the suction pipe of the lifting pump, high-pressure oil pipes, joint sealing rings and cylinder oil ports. Loose suction pipe connections or cracked pipes draw in air, causing pressure fluctuation and lifting jerking. Minor leakage on high-pressure lines results in insufficient pressure and weak lifting. Also check for kinked or squeezed oil pipes that block oil flow.Solution: Tighten all pipe joints; replace cracked pipes and failed sealing rings; straighten deformed pipelines.

II. Core Fault Diagnosis (Main causes for jerking + weak lifting)

1. Air Entering Hydraulic System (Root cause for ~90% jerking faults)

Symptoms: Intermittent jerking and stop-start during lifting; extremely slow lifting at idle speed, slightly improved when engine speed rises; lots of bubbles on oil surface in tank.Causes: Poor sealing of suction pipeline, oil starvation causing cavitation, or air trapped after oil change or maintenance.Air bleeding procedure:

1. Fill hydraulic oil to standard level and tighten all suction pipe joints.

2. With empty cargo box, repeatedly run full lifting-lowering cycles for 3–5 times.

3. Keep engine running at low speed to purge trapped air from the system until lifting is smooth without jerking and no bubbles appear in the tank.

2. Blocked Oil Lines and Dirty Filter Elements

Symptoms: Persistently slow lifting with slight jerking; little difference between cold and hot engine.Causes: Dirty suction strainer and return filter after long service restrict oil flow and return, slowing pressure build-up.Solution: Remove and clean suction strainer and return filter; replace severely clogged filters. Check orifices in oil circuits and clear sludge and impurities to ensure unobstructed oil flow.

3. Lifting Cylinder Faults (Internal leakage, failed seals, sticking)

Symptoms: Marked weakness under heavy load, jerking and sticking in mid-lifting; slight cargo box sinking after parking.Causes: Worn piston sealing rings and failed oil seals of the cylinder cause internal oil leakage and pressure loss. Scuffed cylinder bore, bent piston rod or dry sticking pins increase mechanical resistance.Solution: Disassemble the cylinder and replace the full set of oil seals and sealing rings. Repair lightly scratched cylinder walls; replace cylinder assembly for severe damage. Grease cargo box hinge pins and lifting supports to eliminate mechanical sticking resistance.

4. Worn Hydraulic Pump and Insufficient Pressure

Symptoms: Lifting speed barely increases even at high engine RPM; overall weak performance with faint abnormal noise.Inspection: Connect a pressure gauge to test working pressure. Standard working pressure ≥1.8 MPa. Persistently low pressure indicates pump wear, reduced volumetric efficiency and insufficient oil supply.Solution: For minor wear, adjust the relief valve pressure to restore hydraulic pressure. Replace the gear pump assembly if heavily worn with excessive pressure relief.

5. Stuck or Misadjusted Lifting Valve / Relief Valve

Symptoms: Irregular lifting speed and random jerking; poor oil return and incomplete lifting stroke.Causes: Impurities in oil cause spool sticking in the directional control valve, weakened spring in relief valve, or poor sealing of limit valve, leading to unstable oil circuit switching and fluctuating pressure.Solution: Disassemble and clean spools and valve bodies of control valve, relief valve and limit valve to remove sludge. Recalibrate relief valve working pressure and replace failed springs and seals. Replace valve assembly if spool is heavily worn.

III. Auxiliary Inspection for PTO (Power Take-off)

Incomplete PTO engagement, slipping or insufficient air pressure causes unstable power transmission to the pump, resulting in weak lifting and intermittent jerking.Inspection: Check air tank pressure and air leakage of pneumatic PTO cylinder. Inspect meshing condition between PTO gear and transmission gear. Adjust shims and repair meshing position for abnormal clearance or slipping to ensure stable power transfer.

IV. Post-repair Acceptance & Preventive Maintenance

1. Acceptance Criteria

Lifting and lowering cycles under no load, half load and full load are smooth with no jerking or sticking; uniform lifting speed, stable system pressure, no leakage at pipe joints. The fault is considered resolved.

2. Daily Preventive Measures

1. Regularly check hydraulic oil level and condition; replace hydraulic oil and filter elements every 500 working hours. Do not use inferior oil.

2. Tighten suction pipe joints during routine maintenance to prevent air ingress.

3. Avoid overloading or lifting on slopes to reduce hydraulic system load.

4. Lubricate cargo box hinge points regularly to prevent mechanical sticking that triggers abnormal lifting.