Field diagnosis
Diagnose before you order: 20 field guides for excavator hydraulics
Each guide lists the checks in the order a workshop should work through them, what each result means, and which parts and units usually solve it. Written from the catalogue data and from repair cases we handle.
Browse by area
Pump and pressure supply · Swing, travel and drive assemblies · Boom, arm and cylinder functions · Valve and pilot control · Oil, filtration and the system as a whole
Browse by phenomenon
Slow, weak or stalled — Swing slow, weak or drifting to one side, Tracks weak, one side not moving, No pressure / no power at the pump, Engine stalls or smokes under load, All functions slow, Controls sluggish or dead, Proportional pilot control reacts late, in steps, or not at all
Drift, creep or jerky movement — Cylinder drifts down under load, Spools stick or lock when cold, Movement stutters or crawls when the lever is barely open
Noise, vibration or shock — Noise, vibration and rising oil temperature, Final drive noisy or metal in gear oil, Hoses burst, seals blow, the gauge needle jumps
Overheating and climate — Oil temperature keeps rising, Machine slow or noisy when cold, Machine weak when it is hot
Oil condition — Metal particles, dirty oil, short component life, Foam or milky hydraulic oil
Repair or replace — Case drain flow above specification, Repair the pump or replace it
Or start from the symptom you can see: Slow, weak or stalled (7) · Drift, creep or jerky movement (3) · Noise, vibration or shock (3) · Overheating and climate (3) · Oil condition (2) · Repair or replace (2)
Pump and pressure supply
Pressure, delivery, wear and the pump-engine match: the guides that start at the source of the oil. Open the area page →
No pressure / no power at the pump
No pressure is rarely the pump alone. Use this checklist to separate pump wear from control, suction and relief problems in under an hour.
Noise, vibration and rising oil temperature
Noise plus heat usually means air, starvation or internal leakage. Which one you have changes what you order.
Engine stalls or smokes under load
When the engine pulls down, the pump is usually asking for more torque than the engine can deliver. These checks separate an engine fault from a pump control fault.
Case drain flow above specification
Case drain flow shows how worn a pump or motor is without removing it. Here is how to measure it so the number actually means something.
Swing, travel and drive assemblies
Motor and reduction-gear complaints: slow swing, weak travel, run-away, noise and metal in the gear oil. Open the area page →
Swing slow, weak or drifting to one side
Slewing feels sluggish or refuses to hold a load. Nine times out of ten it is not the whole swing assembly - this is the order to check, and what each result points to.
Tracks weak, one side not moving
A travel fault looks expensive, but the checks are cheap. Work through them in this order before ordering a travel drive assembly.
Final drive noisy or metal in gear oil
Noise from a travel reduction gear, or metal on the drain plug, has three usual sources. Check them before the spline fails and takes the motor with it.
Boom, arm and cylinder functions
The working functions: drift, creep, jerky movement and every-function-at-once complaints. Open the area page →
All functions slow
When travel, swing, boom and bucket are all slow, the fault sits upstream of the individual circuits. Work these system checks before ordering anything.
Cylinder drifts down under load
Drift is a leakage question. These checks tell you whether oil is passing the piston seal, the control spool or the holding valve before you remove anything.
Movement stutters or crawls when the lever is barely open
A function that moves smoothly at speed but stutters when the lever is barely open is fighting friction or air, not power. The cure is usually in the valve, the cylinder seal or the stiffness of the circuit.
Valve and pilot control
Spools, pilot pressure, proportional solenoids and pressure transients: the control layer between lever and load. Open the area page →
Spools stick or lock when cold
A spool that sticks when cold, or grabs in one position, is telling you about oil cleanliness, varnish or bore damage. Fix the cause, not only the spool.
Controls sluggish or dead
Pilot pressure moves every control spool. When it is low the whole machine feels tired even with a perfectly healthy main pump.
Hoses burst, seals blow, the gauge needle jumps
Hoses failing in the same place, filters splitting or a gauge needle that jumps are transient problems. Steady pressure tells you nothing about them - here is what to measure and what to fix.
Proportional pilot control reacts late, in steps, or not at all
Machines with proportional pilot control fail in a characteristic way: the function arrives late, arrives in steps, or does not arrive at all. It is usually current, contamination or wiring - in that order.
Oil, filtration and the system as a whole
Oil condition, water and air, cleanliness, climate and the system-level decisions that follow. Open the area page →
Metal particles, dirty oil, short component life
Contamination is the number one cause of repeat failures. Here is what to do after a failure so the new pump is not destroyed by the old oil.
Oil temperature keeps rising
Over-temperature thins the oil and shortens seal life, so every function weakens. Find out whether the heat is being generated or simply not removed.
Foam or milky hydraulic oil
Foam means air, milkiness means water, and both destroy the lubrication film. These checks find the entry point instead of changing the oil again.
Machine slow or noisy when cold
In low ambient temperatures the oil is the problem, not the pump. A short warm-up routine prevents the damage behind slow, noisy cold shifts.
Machine weak when it is hot
In high ambient temperatures the hydraulic system runs near its thermal limits. These measures protect flow, pressure and seal life through the shift.
Repair the pump or replace it
The decision follows measurable evidence, not the age of the machine. Work through these six points and the answer is usually obvious.
The principle behind the symptom
Every guide above links to the technical articles that explain the mechanism. If you would rather start from the theory, the articles are grouped by topic as well.
Field diagnosis and maintenance
Testing methods, cleanliness targets and the habits that keep a machine measurable.
Components and valves
Why a spool sticks, whistles or feels heavy - the mechanism behind control symptoms.
Systems and control
Matching, speed control and closed circuits: what the machine is doing when it works well.