Final Drive Failure Symptoms: When to Stop Running It

On an excavator, the final drive is the unit each sprocket bolts to: a hydraulic travel motor turning a planetary gearbox in its own gear oil. Some signs point at the gearbox, some at the motor and a few at neither, and that changes what you order.

What does a failing final drive sound like?

It grinds, whines, clunks or knocks, and the noise that matters is new or louder than last week. Listen as the machine travels slowly on firm ground, both ways and through a turn, with anyone outside well clear of the tracks.

What you hear	What it usually means	What to do
Grinding	Gear teeth or bearings running metal on metal, often on low oil	Stop. Once it has cooled, have the oil and magnet checked
A whine or growl that rises with speed or load	Gear mesh wear, or a bearing going rough	Have the oil checked for metal, and plan the repair
A clunk or knock when you change direction	Slack in the drive: worn splines or gear teeth, or loose bolts	Check the sprocket and mounting bolts
A knock at a steady beat	A damaged tooth, or something caught in the sprocket	Clean the undercarriage. If it stays, have the oil checked

A whine you hear with the tracks standing still is not the final drive, which turns only when the machine travels. The pump is a likelier source.

Why is my final drive leaking oil?

Gear oil outside the drive usually comes from the floating face seal, or duo-cone seal. It sits in the gap between the drum, which turns with the sprocket, and the spindle bolted to the track frame. A leak there leaves a wet ring on the back of the sprocket.

Oil around the motor’s hoses and fittings is more often hydraulic oil. That is a different repair, so establish which oil it is first.

A face seal leak starts a clock. The gap that lets oil out lets water and grit in, and the oil becomes lapping compound. The bearings wear first, then the gears, running out of line on worn bearings. Topping up puts oil back and leaves the grit inside.

Wire or rope wound into the seal gap is a common start. A seal that only weeps, with the level holding between checks, can be planned for. One that lets the level fall cannot. Replacing it means taking the drum off the spindle: a technician’s job. Our paper on floating face seals traces the damage step by step.

What is the gear oil telling you?

Never open a drain or fill plug on a drive that has been working. The oil is hot, and the case can be under pressure. Let the drive cool and follow the manual, or leave it to a technician.

• Level falling. Oil is leaving, usually at the face seal or a plug.
• Milky oil. Usually water, let in by the face seal.
• Dark, with a burnt smell. It has run hot: something is dragging, or the level ran low.
• The magnet. A little fine gray fuzz is ordinary wear. Glitter in the oil, or a thick paste on the magnet, is wear speeding up. Flakes, chips or chunks mean a gear or bearing is breaking up.

Gear oil that rises between checks, or drains thin and smelling of hydraulic oil, probably has hydraulic oil in it. It comes from the motor side, most often past the motor’s shaft seal. That seal fails with wear, or when a restricted case drain lets pressure build in the motor case.

A technician confirms the source and checks the motor’s case drain against the machine’s figure. Meanwhile the thinned oil protects the gears less, and the overfilled case can push oil out past the face seal. A new face seal will not cure it. If the motor is worn and the gearbox sound, the fix may be a travel motor alone.

Weak or slow travel on one side

A drive losing power shows it on its own side. That track lags, the machine pulls toward it, or it creeps on a slope with the levers in neutral.

In the drive, a worn travel motor leaks internally and loses pull under load. A parking brake that drags slows the track, and one that will not hold lets the machine creep. On most excavators the brake sits in the travel motor.

The pump, the travel valve, the swivel joint that feeds the tracks or a hose can cause the same signs. Telling them apart takes flow and pressure tests by a technician, since the circuit can hold pressure after shutdown. More in why an excavator tracks to one side.

Is one final drive overheating?

After the same work, both drives usually run at about the same temperature. One much hotter than the other is probably dragging: a brake not fully releasing, a failing bearing, low oil, or an overfilled case.

Compare them with an infrared thermometer on the same spot of each hub, with the machine parked and shut down. Never judge it by hand: a hub hot enough to matter can burn you. There is no figure to aim for. The difference between the two sides is the reading.

Sprocket wobble, end play or loose bolts

On most drives the drum turns on a pair of main bearings held under preload. When they wear or lose it, the sprocket wobbles as it turns and the drum has end play a technician can measure. The play can also part the face seal, so a new leak may be the first sign.

Loose sprocket bolts show as a clunk on direction change, a rust trail from under a bolt head, or a missing bolt. Left loose, the holes wear oval and the remaining bolts break. Bolts that have run loose may be stretched: the manual says whether to fit new ones, and how tight. If they loosen again, the mating faces may be worn. Check the bolts holding the drive to the frame too.

What to rule out before blaming the drive

Three things pass for a failing drive and are easy to check.

• Packed debris. Mud or rock in the sprocket, rollers and idler makes one side noisy and slow.
• Track tension. Too tight, it loads the drive’s bearings all day; too slack, the track slaps and clunks. Check it against the manual after cleaning, since packed mud tightens a track, and adjust it by the manual: the adjuster holds grease under high pressure. A rule of thumb is not a specification.
• A hose. A kinked travel hose can weaken travel on one side, and a weeping one can pass for a drive leak. Never feel for a leak by hand: a pinhole jet can inject oil through skin, which needs a hospital at once.

Can you keep running a failing final drive?

Sometimes, for a while, but not with every sign.

Stop now if you find:

• Grinding, or any noise getting louder by the day.
• Flakes, chips or chunks on the magnet.
• Oil running out, or a case found low or empty.
• One hub much hotter than the other.
• A wobbling sprocket, or a drive that jerks, locks or slips.
• A track that suddenly turns freely or will not hold. On most drives the brake acts on the motor, ahead of the gears, so a broken gear train leaves that track free.

Plan the repair, and check more often, if you find:

• A weeping seal, with the level holding.
• Glitter in the oil, or more fuzz on the magnet than last time.
• A steady whine, with the oil clean and full.
• Gear oil rising or thinning. Have the motor side checked soon.
• Slightly slower travel on one side, with no noise or heat. Have the hydraulic side tested.

A seal or bearing job caught early is a repair. The same fault run to the end is a complete drive.

When should you replace the final drive?

Once gear teeth are spalled or broken, or the drum or spindle is cracked, a repair renews most of the drive. Replacing it usually makes more sense then, as it does when the main bearings have worn their seats or a fault comes back after a repair. For what moves the bill, see final drive replacement cost.

Whatever you fit, find what killed the old drive first. The final drives page lists the usual causes. If the drive may be under warranty, talk to the dealer who supplied it before anyone opens it, and read how a claim runs.

For the right replacement, send the number on the drive’s tag and the machine’s make, model and serial number. Add what you found, since it decides whether you need the complete drive, the gearbox or only the motor. No tag? See finding a final drive part number. Then send it all through the request form, or to a dealer from the dealer finder.