08-11-2025, 10:36 PM
Introduction
Hydraulic systems power critical motions in Lull telehandlers—from boom extension to steering and braking. When pressure drops or fluid flow falters, productivity slows, and safety risks increase. Understanding common symptoms and how to diagnose them is essential for swift, effective repair.
Symptom: Total Hydraulic Loss Yet Transmission Still Works
One operator reported a scenario where the machine could drive, but its brakes barely released due to nearly nonexistent hydraulic pressure—only 190 psi standby pressure remained, while nominal values should exceed that by about 25 psi. Despite replacing the main valve, pump, and accumulator cartridge, the issue remained unresolved, pointing to possible accumulator or circuit-level faults.
Symptom: Slow, Weak Hydraulic Response Especially in Cold Weather
A 1044C-54 unit developed sluggish boom and tilt movements during winter starts. Pilot circuit pressure remained steady, but boom lift pressure dropped rapidly when revved. After inspecting filters and pumps, attention shifted toward selector valves and coil components, since they often influence control responsiveness in cold conditions .
Symptom: Hydraulics Surging in Cycles Every Few Seconds
Another telehandler model experienced pressure surges every 3–5 seconds, leading hoses to stiffen rhythmically. Accumulators were suspected culprits—and measuring full-system pressure with high-range gauges was recommended to isolate intermittent leakage or recharge behavior .
Glossary of Key Terms
One veteran recalled an old Highlander machine moving concrete forms. The boom suddenly surged out nearly two feet upon startup—unexpected and violent, nearly tipping cargo. Cycling the controls with engine off seemed to relieve trapped pressure. Such mysterious jerking motions often trace back to failing counterbalance or pilot valves that aren't holding pressure stably .
Structured Troubleshooting Steps
1. Start with Fluids and Filters
Common Symptoms:
Lull telehandlers deliver powerful versatility—but their hydraulic systems demand respect and methodical diagnostics. By starting with fluid basics, measuring pressure, testing control components, and having accurate system diagrams, you can restore smooth, safe performance, even when symptoms seem enigmatic.
Hydraulic systems power critical motions in Lull telehandlers—from boom extension to steering and braking. When pressure drops or fluid flow falters, productivity slows, and safety risks increase. Understanding common symptoms and how to diagnose them is essential for swift, effective repair.
Symptom: Total Hydraulic Loss Yet Transmission Still Works
One operator reported a scenario where the machine could drive, but its brakes barely released due to nearly nonexistent hydraulic pressure—only 190 psi standby pressure remained, while nominal values should exceed that by about 25 psi. Despite replacing the main valve, pump, and accumulator cartridge, the issue remained unresolved, pointing to possible accumulator or circuit-level faults.
Symptom: Slow, Weak Hydraulic Response Especially in Cold Weather
A 1044C-54 unit developed sluggish boom and tilt movements during winter starts. Pilot circuit pressure remained steady, but boom lift pressure dropped rapidly when revved. After inspecting filters and pumps, attention shifted toward selector valves and coil components, since they often influence control responsiveness in cold conditions .
Symptom: Hydraulics Surging in Cycles Every Few Seconds
Another telehandler model experienced pressure surges every 3–5 seconds, leading hoses to stiffen rhythmically. Accumulators were suspected culprits—and measuring full-system pressure with high-range gauges was recommended to isolate intermittent leakage or recharge behavior .
Glossary of Key Terms
- Standby Pressure – Baseline pressure in the hydraulic circuit when idle, needed to hold functions or release brakes.
- Accumulator – A reservoir that stores pressurized fluid to smooth system response and energy use.
- Pilot Circuit – Low-pressure control lines that trigger main valve spools in response to operator inputs.
- Selector Valve & Coils – Components that direct hydraulic flow; coils are electrical elements that shift hydraulic spool positioning.
- Hydraulic Filters/Suction Screens – Prevent debris from damaging pumps; clogging here can starve the system of fluid despite pumps spinning normally.
One veteran recalled an old Highlander machine moving concrete forms. The boom suddenly surged out nearly two feet upon startup—unexpected and violent, nearly tipping cargo. Cycling the controls with engine off seemed to relieve trapped pressure. Such mysterious jerking motions often trace back to failing counterbalance or pilot valves that aren't holding pressure stably .
Structured Troubleshooting Steps
1. Start with Fluids and Filters
- Check hydraulic fluid level and viscosity.
- Replace or clean suction filters and high-pressure screens—even minor residues can cause cold-start pressure drops .
- Confirm standby pressure matches spec; low values hint at accumulator or unloader valve trouble .
- Use calibrated gauges to test pump output, accumulator, brake, and pilot circuit pressures.
- Test selector valve function and coil resistance—electrical issues here can cut off pilot signals or restrict fluid paths .
- Look closely at accumulator performance—if cycling or surging continues, leakage may force it to recharge too often .
- Counterbalance valves and pilot checks must maintain pressure when idle. If the boom drifts or shoots out unpredictably, these might be compromised .
- Hydraulic systems are complex, especially when they incorporate gear pumps, reload circuits, and closed-center designs. Having proper schematics based on model and serial number is vital—don’t proceed without them .
Common Symptoms:
- Transmission moves, but hydraulics barely respond
- Slow operation on cold start; improves as heat builds
- Regular (every few seconds) hydraulic surges
- Boom or carriage drifts or jerks unpredictably
- Low fluid level or wrong hydraulic oil viscosity
- Clogged suction or pressure filters
- Failing accumulators or unchecked standby pressure
- Faulty selector valves, coils, or valve holding mechanisms
- Model-specific design quirks—always cross-check schematic
Lull telehandlers deliver powerful versatility—but their hydraulic systems demand respect and methodical diagnostics. By starting with fluid basics, measuring pressure, testing control components, and having accurate system diagrams, you can restore smooth, safe performance, even when symptoms seem enigmatic.
