Field diagnosis
Swing slow or weak: check this before replacing the swing motor
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.
Check these in order
| Check | What it looks like | What it tells you |
|---|---|---|
| Relief valve setting | Swing relief pressure below specification makes every movement slow, with no other symptom. Gauge the relief valve port against the specification sheet. | If low, the relief cartridge or its setting is the first suspect - not the motor. |
| Brake release pressure | The parking brake releases on pilot pressure. Insufficient release pressure drags the brake and heats the oil. | Check the release line at the brake port, and the pilot pressure at the same time. |
| Make-up (oil filling) valve | A worn make-up valve allows cavitation on the return side, which shows up as noise and slow acceleration rather than a hard failure. | Inspect the valve and its spring; replace the cartridge kit. |
| Motor internal leakage | Case drain flow that exceeds a few litres per minute at working temperature means the piston and slipper pair is worn. | Measure case drain flow; a worn rotary group is a repair-kit job, not always a new assembly. |
| Pilot circuit and control valve | If swing is slow in one direction only, the control valve spool or the pilot line is usually at fault. | Swap pilot lines left to right to isolate the circuit before condemning the motor. |
| Reduction gear (FRG) | Gear oil condition and backlash matter: metal in the oil means the planetary set is failing, and a slow swing is only the first symptom. | Drain and inspect the gear oil, then check backlash per the drawing. |
Units and parts this usually leads to
M5X130CHB
12–15 t hydraulic excavator - 121.6 / 129 / 129.2 cm³ (motor variants)
M5X180CHB
20–25 t hydraulic excavator - 148.5 / 169.4 / 180.1 cm³ (motor variants)
Field notes on this complaint
The notes our own team works to on this symptom. Each one is a principle you can check on the machine, a step from the case-drain and cleanliness procedure we follow, or a figure transcribed from our catalogue - not advice copied from a video or a forum. Anything we could not check against a catalogue, a manufacturer document or a working machine is left out.
- Swing relief and brake release. Slow swing with normal main pressure usually points at the swing relief setting or the brake release pressure rather than the motor internals. (circuit principle, checkable on the machine)
- Case drain on the swing motor. The working-temperature case-drain test we use on pumps applies here too, and tells you whether the motor internals are worn. (our own case-drain and cleanliness procedure)
- A stripped key or spline looks like a failed motor. On swashplate-type units the cylinder block sits coaxially with the drive shaft and is driven through a key or a spline. If that connection strips, the symptom is exactly 'the swing motor turns but the machine does not' - check the coupling and the shaft before the internals. (circuit principle, checkable on the machine)
Common questions
How do I know if the swing motor or the control valve is at fault?
Test swing speed in both directions. If one direction is clearly slower, look at the pilot line and spool first; if both are equally slow and relief pressure is correct, measure motor case drain flow.
Can a swing motor be repaired instead of replaced?
Yes. Rotary-group wear is a repair-kit job: piston and slipper set, cylinder block, valve plate and seal kit are all available separately for M5X130CHB and M5X180CHB.
What brake torque should I expect?
M5X130CHB is rated around 874 Nm and M5X180CHB around 1,210 Nm maximum brake torque from the catalogue - confirm against your unit nameplate.
Why it happens
The mechanism behind this symptom, from our technical articles: reading the principle first usually shortens the checklist.
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