Slow or weak hydraulics: how to tell if the pump is failing

Five cheaper causes to rule out first

1. Oil level and oil condition. Check it cold, on level ground, with every cylinder in the position the manual calls for. A tank a few inches low lets the pump pull air on slopes and in turns. Milky oil has water in it, black oil that smells burnt has been overheated, and either one will make a good pump behave like a bad one.
2. Suction strainer and filter. The strainer inside the tank on the pump inlet is the most forgotten service item on a farm tractor. Plugged, it starves the pump, which whines, cavitates and eventually eats itself. A return filter past its bypass pressure does less harm but tells you the oil is dirty.
3. Air in the system. Foam in the tank, a spongy feel on the levers, a pump that growls. A loose suction fitting, a cracked suction hose or a shaft seal on the pump can all pull air in without leaking oil out, because the suction side runs below atmospheric pressure.
4. Relief valve. The main relief sets the maximum pressure the pump can build. A weak spring, a stuck poppet or a setting someone backed off in the past means the whole machine is weak at full pressure and everything stalls early under load. Cheap to test with a gauge and often cheap to fix.
5. One cylinder or motor bypassing. A cylinder with worn piston seals is a hole in the circuit. On some machines a single badly bypassing cylinder drags the whole system down and heats the oil, because the pump is pushing flow straight across the piston to tank. If one function is much weaker than the rest, start there, not at the pump. The guide on cylinder drift covers how to spot that one.

Signs that really do point at the pump

• Everything is slow, and slower hot. Every function on the machine weak together, with a clear drop after the oil warms up, and the checks above all came back clean.
• Metal in the filter or the tank. Fine bronze or steel fuzz on the filter element or the drain plug magnet. A pump shedding metal is a pump on its way out, and the metal is already in every valve downstream.
• Heat at the pump. A pump body noticeably hotter than the tank and the lines around it is turning horsepower into heat instead of flow.
• Leak at the shaft seal. Oil at the pump shaft is often a symptom of case pressure or a worn shaft bearing rather than just a seal, and it is where air enters on the suction side.
• The flow test says so. This is the one that counts. A pump that cannot deliver its rated flow at working pressure with warm oil is worn, and no amount of strainer cleaning brings it back.

What the diagnostic visit actually does

The visit is a pressure and flow test on the machine, priced on the cost page at $195 to $450 and credited against the repair if we do the work. The machine is run up to operating temperature, because a cold test flatters a worn pump. A gauge on the pressure side shows whether the relief is opening where it should. A flow meter in the circuit shows how much oil the pump delivers at low pressure and then under load, and the difference between those two numbers is the pump's condition in one figure. If the pump is healthy, the meter moves to the individual functions until the one that is losing the flow shows itself. You get the readings and what they mean before any part is priced, and if the answer is a strainer and a fill, that is the answer you get.

What each outcome costs

• Oil, strainer, filter, suction hose: parts and the labor to do them, on the shop rate of $125 to $155 an hour or the field rate of $145 to $185. Often the whole answer.
• Relief valve: a spring and seal kit or a new cartridge, priced live for the make, and a reset with a gauge on it.
• Control valve section: $300 to $1,200 for a rebuild, depending on sections and whether the body is scored.
• Pump or motor: $800 to $4,000. A gear pump rebuild sits near the bottom, a piston pump or a closed loop drive motor near the top. Where a pump failed and shed metal, the system flush is quoted separately and we say when it is needed.

Mobile calls carry the trip fee of $150 to $235 once per visit. Bring the machine or the pump to the shop in Woodland and there is no fee.

Two calls where the pump was not the answer, and one where it was

A row crop tractor near Knights Landing, everything slow and the pump whining after twenty minutes of work. The suction strainer had never been out of the tank and was packed with years of sediment. Cleaned it, changed the oil, and the whine and the slowness went with it. Caught in time, the pump was fine.

A lift truck in a West Sacramento warehouse that stalled out lifting a full pallet but tilted and steered fine. A gauge on the lift circuit showed the relief opening far below where it should. A weak relief spring, not a pump, and the truck was back on the dock the same shift.

An excavator on a Dixon job site, slow on every function, oil dark and hot, bronze fuzz on the filter. The flow test at temperature confirmed a worn pump. That one was a pump, a flush, new filters and a conversation about how the metal had already reached the control valve.

What to have ready when you call

1. Is every function slow, or just one?
2. Is it worse hot? Roughly how long before it fades?
3. Any new noise from the pump, and does it change with engine speed?
4. Oil level and what the oil looks like on the dipstick or sight glass.
5. When the strainer, filter and oil were last done, if you know.

With those answers we can usually say on the phone whether this looks like a supply problem or a worn pump, give you the range, and book the test. During harvest the truck runs the routes on the farm equipment page, and a machine that is slow but still moving is worth calling before it is a machine that is stopped.

Slow hydraulics and pump questions