Condition · 7 min
Hydraulic cycle times and the drift test
How do you test the hydraulics on a used excavator without a pressure gauge?
Time every function at full throttle at operating temperature and compare each against the manufacturer's specification for that model. Read the pattern: a consistent 15–25% slowdown across all functions indicates pump wear, while slowdown on one function alone points to that circuit's valve or cylinder. Then measure drift — raise the boom fully, hold the machine still, and measure rod extension loss over five minutes with a steel rule. Repeat for stick and bucket. Movement beyond specification indicates cylinder seal or holding-valve leakage.
You do not need a pressure gauge to find out whether an excavator’s hydraulics are tired. You need a stopwatch, a steel rule, somebody who can operate the machine consistently, and twenty minutes.
Almost nobody does this. It is the largest gap between what a careful buyer could know and what a typical buyer actually knows.
First: the machine must be at operating temperature
This is the opposite of the engine test, and people get the two confused.
The engine must be cold for the start test — that is where hard starting, blowby and start smoke show up.
The hydraulics must be warm for the timing test. Cold oil is thicker and everything is slower, so timing a cold machine produces numbers that mean nothing and usually condemn a healthy pump.
So the sequence is: cold start first, watch what you need to watch, then run it up to temperature, and only then start the stopwatch.
Timing the functions
Time each of these at full throttle, through the full travel of the function, with the machine standing still:
- Boom raise, and boom lower
- Stick in, and stick out
- Bucket curl, and bucket dump
- Full slew, both directions
- Track, both sides
Run each one at least twice and use the slower figure. Have the same person operate throughout — a different operator changes the numbers more than a worn pump does.
Then compare each against the manufacturer’s specification for that exact model. That last bit matters: cycle times vary considerably between variants of the same machine, and a figure from a similar model is not a specification, it is a guess wearing a specification’s clothes.
If you cannot get the real figures for the model in front of you, say so and treat your numbers as a baseline for comparison against another machine — not as a pass or fail.
Reading the pattern, not the numbers
This is where the diagnosis actually happens, and it is simple enough to remember.
Everything is slow, by roughly the same amount. A consistent degradation of about 15–25% across all functions points at pump wear. The pump is delivering less flow than it should, and every circuit downstream feels it equally. This is the expensive answer.
One function is slow, the rest are normal. That points at that circuit — its control valve section, or its cylinder. Everything else being healthy tells you the pump is fine. This is the cheaper answer, and often a great deal cheaper.
Everything is slow, but wildly inconsistently. Check the obvious things first: oil level, oil condition, filter service history, and whether the engine is actually reaching full rated speed. A machine that cannot make its revs cannot make its cycle times, and that is an engine finding, not a hydraulic one.
The drift test
This takes five minutes and, in our experience, finds more than the previous hour of timing.
- Raise the boom fully, to the top of its travel.
- Hold the machine completely still. Engine off is cleanest, if the machine holds with the engine off.
- Mark the exposed cylinder rod, or measure the exposed rod length with a steel rule.
- Wait five minutes.
- Measure again. Record the loss in millimetres.
Repeat for the stick and the bucket.
Movement beyond the manufacturer’s allowance indicates leakage past the cylinder seals or through the holding valve. Which of the two it is takes further work to establish, but knowing that it drifts, and by exactly how much, is the finding that matters at the point of purchase.
Write down the millimetres. “It drifted a bit” is not a measurement and cannot be negotiated with. “Boom drift 11 mm in five minutes” can.
What drift actually costs you
Drift is not a cosmetic complaint. A machine that will not hold a load is a machine that cannot be trusted for precise work, and on some sites it is a safety conversation rather than a productivity one. It also gets worse, not better.
What this cannot tell you
Be honest about the limits, because a test that is oversold is worse than no test.
- It does not tell you the internal condition of the pump — only that flow is down.
- It does not distinguish a worn cylinder from a leaking holding valve without further testing.
- It does not tell you about relief valve settings, which need a gauge.
- It assumes the oil is in reasonable condition and at the right level. Check both first, or you are measuring the wrong thing.
A proper diagnosis with gauges is a workshop job. The point of this method is that it tells you, on a yard, in twenty minutes, whether the machine in front of you needs one.
What to do with the numbers
Take them into the negotiation as figures, not impressions.
A machine that is 20% down across every function is not necessarily a machine to walk away from — it is a machine whose price should reflect a pump. What kills buyers is not buying a tired machine; it is buying a tired machine at the price of a healthy one because nobody measured.
On a full inspection, timed cycles and a five-minute drift measurement on all three functions are part of the standard protocol, alongside the undercarriage measurements and the engine and structural checks. The hydraulics grade that comes out of it is one of five that can cap the overall grade of the machine.