Final drive has no power: causes and checks
Zoltan Gal, Managing Director FinalDriveUpdated
If only one side lacks power, the cause is usually that side's travel motor, the rotary joint (swivel) or the control valve. If both sides are weak, the hydraulic pump, the engine or the system pressure is more likely. Swapping the supply lines left and right narrows it down quickly.
An excavator that has no travel power, pulls to one side or stalls on a slope does not necessarily have a faulty final drive. The hydraulics before the drive can just as well be the cause. Before you replace parts, a systematic check pays off.
Typical signs
- The machine travels slower than usual or can no longer climb a slope.
- The excavator pulls to one side when driving straight.
- When counter-rotating, one track stops.
- Second speed does not engage or drops out under load.
- The drive gets unusually hot or makes noise.
Causes at a glance
| Observation | Likely cause |
|---|---|
| Both sides weak, boom and bucket slow too | Hydraulic pump, engine, oil level or filter in the hydraulic system |
| Only one side weak | Travel motor on that side, rotary joint, control valve or brake |
| Weak only in second speed | Shift valve in the travel motor or pilot line for second speed |
| Power loss and noise, chips in the gear oil | Internal damage in the planetary gearbox or travel motor |
| Track hard to move, drive hot | Track tensioned too tight or brake not releasing |
Narrow it down step by step
- Check hydraulic oil and filter. Too little oil, a clogged filter or air in the system weakens all functions.
- Check track tension. An over-tensioned track slows the machine and loads the drive bearings. Adjust tension according to the operator's manual.
- Visual check of the drive. Wire, rope or stones in the sprocket block the track and damage the floating seal.
- Swap lines left and right. Swap the two supply lines of the travel motors at the rotary joint or valve. If the problem moves to the other side, the cause is before the drive (valve, rotary joint). If it stays on the same side, the travel motor itself is suspect.
- Check case drain flow. If clearly more oil runs from the case drain line than on the other side, pistons or valve plate in the travel motor are worn. This test belongs in a specialist workshop.
- Check the gear oil. Metal chips mean internal damage. If the gearbox oil level rises, hydraulic oil is passing a failed seal into the gearbox.
If the travel motor is the cause
A worn travel motor usually needs an overhaul or a new final drive. Which pays off more is covered in repair or replace a final drive. We supply the complete drive, travel motor and planetary gearbox in one unit, for more than 50 excavator brands. The page excavator final drives lists all models from mini to large crawler excavators by weight class.
Common mistake after a swap
If power is missing after fitting a new drive, a line is often swapped or the case drain line is not connected correctly. A pressurised case drain destroys the shaft seal in the travel motor. How to assign the lines safely is explained in removing and installing a final drive.
Frequently asked questions
Why does my mini excavator pull to one side?
Usually one travel motor is losing power, the rotary joint is leaking internally or a control valve is sticking. Unequal track tension can also be the cause.
How do I test whether the travel motor is faulty?
Swap the supply lines left and right. If the fault moves, it lies before the drive. If it stays on the same side, the travel motor is suspect.
Can an over-tensioned track cost power?
Yes. An over-tensioned track noticeably slows the machine and loads the bearings in the final drive.
What does a rising oil level in the gearbox mean?
Hydraulic oil from the travel motor is entering the gearbox, usually via a failed shaft seal. A common cause is a blocked or wrongly connected case drain line.