Field diagnosis
Tracks weak or one side not moving: travel fault diagnosis
A travel fault looks expensive, but the checks are cheap. Work through them in this order before ordering a travel drive assembly.
Check these in order
| Check | What it looks like | What it tells you |
|---|---|---|
| Track tension and undercarriage | A seized idler or over-tight track loads the drive and feels like a weak motor. | Free the undercarriage first, then re-test. |
| Travel relief pressure | Low relief pressure makes both sides weak and is often a cartridge issue. | Gauge each travel circuit separately; a difference between sides points at the motor or brake valve. |
| Balance valve / counterbalance | The balance valve holds the machine on a slope and meters flow. A sticking valve causes weak travel and drift. | Inspect the valve spool for scoring and the spring for fatigue. |
| Brake release | The travel brake must release fully. Partial release heats the case and reduces output torque. | Measure release pressure at the brake port; compare with specification. |
| Case drain flow | Compare case drain on both sides at the same oil temperature - a difference of more than the specification indicates internal wear. | A worn side can be repaired with a rotary-group kit or replaced as an assembly. |
| Reduction gear oil | Metal in the travel gear oil means the planetary is failing; continuing to work will destroy the housing. | Drain, inspect and replace oil before further operation. |
Units and parts this usually leads to
FTD45
18–22 t excavator / drilling rig / crawler crane →
FTD48
22–26 t excavator / drilling rig / crawler crane →
FTD26
13–16 t excavator / drilling rig / crawler crane →
FDNB08
5–6 t excavator →
FDNB12
8–10 t excavator →
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.
- Both tracks or one track. Weak travel on both tracks points at the travel relief or the pilot pressure; weak on one track points at that motor or its final drive. (circuit principle, checkable on the machine)
- A dragging brake heats and slows. A travel motor whose brake does not fully release drags and heats; check the release pressure before condemning the motor. (circuit principle, checkable on the machine)
- Torque follows the pressure difference. Motor torque is proportional to the difference between inlet and outlet pressure, so a weak travel motor is first a pressure question: measure both sides at working temperature and compare with the manual before opening the motor. (circuit principle, checkable on the machine)
- Motor torque is quoted per 100 psi - so measure pressure, not sound Hydraulic motors are rated by torque per unit of pressure drop, usually expressed as torque per 100 psi or per 10 bar. That makes the pressure you measure at the motor ports the first number to write down: if the motor produces the right torque at the specified pressure drop, the fault is mechanical (gearbox, bearings, tracks); if it needs far more pressure for the same movement, the motor or a circuit bypass is the suspect. (circuit principle, checkable on the machine)
- Charge pressure dropping when you move is normal - the charge pump changes sides In a closed loop the charge (replenishment) pump at neutral feeds both the A and B sides, all of its flow leaves over the charge relief, and the gauge shows that relief setting. Put the pump into displacement and the charge flow follows whichever side is now the low side - the gauge drops a little, and flow over the charge relief stops being the rule. So a small drop as you move is normal; a drop that keeps falling, or does not recover when you stop, is the charge pump, the relief or a leak in the loop. (circuit principle, checkable on the machine)
- The charge pump is protection, not an accessory - a collapse damages both ends The charge (replenishment) pump is a smaller pump inside the main hydrostatic pump; it makes up the oil the loop loses through leakage, feeds the control circuit and keeps the low side supplied. If charge pressure falls too low - a failed charge pump, a closed relief, a big loop leak - the main pump and the motor stop receiving make-up oil, and the failure can be destructive rather than gradual. When travel or swing is weak, charge pressure is the first number to measure. (circuit principle, checkable on the machine)
Common questions
How do I compare the two travel motors properly?
Measure the same thing on both sides at the same oil temperature: case drain flow, relief pressure and travel speed. Differences matter more than absolute numbers.
What is the most common cause of one-side travel failure?
Spline or coupling failure between motor and reduction gear, followed by pilot or valve blockage. Open the coupling cover before condemning the motor.
Which travel assemblies do you supply?
FDNB08 and FDNB12 for 5-10 t, FTD26 for 13-16 t, FTD45 for 18-22 t and FTD48 for 22-26 t, with the catalogue torque and ratio figures on each model page.
Why it happens
The mechanism behind this symptom, from our technical articles: reading the principle first usually shortens the checklist.
Closed-circuit hydrostatic drives: why travel and swing use pump control
Systems and control
How a closed-circuit hydrostatic drive works: variable pump, motor, relief valves and charge pump; why it wastes less energy than ...
Travel and swing drives: three numbers that decide whether a hydrostatic drive lasts
Systems and control
Charge pressure, case drain flow and control response - measured hot - tell you whether a pump-controlled drive is healthy. How to...
Swing, travel and the four quadrants: why a motor is not a cylinder
Systems and control
A motor is symmetric, so speed and flow behave simply - but it works in four quadrants, and in two of them the load is in charge. ...
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