Excavator Travel Motor Problems: Causes of Weak Travel, Engine Lugging, Jerking, Slow Speed, and Sticking

Excavator travel motor problems is a broad term. In actual troubleshooting, the symptoms may include:

• Weak travel on one side
• Weak travel on both sides
• Engine lugging during travel
• Sticking or intermittent travel
• Slow travel speed
• Jerking or surging while traveling
• Failure to switch between high and low travel speed

Different symptoms are caused by different faults. To diagnose the problem correctly, it is helpful to first understand how the excavator travel system works.

1.How Does an Excavator Travel Motor System Work?

The engine is the primary power source of an excavator. When the engine is running, it drives the main hydraulic pump and the pilot system.

Most hydraulic excavators use variable-displacement piston pumps as the main pumps. The pilot system may use a gear pump or pressure-reduced oil supplied from the main hydraulic circuit.

The main pump sends high-pressure hydraulic oil to the main control valve. At the same time, pilot pressure oil is supplied to the pilot control valves in the cab.

When the operator moves the travel levers or pedals, the pilot valve produces control pressure. This pressure moves the corresponding travel spool inside the main control valve.

The main control valve then directs hydraulic oil to the travel circuit.

The basic oil flow path can be understood as:

Engine → Main Hydraulic Pump → Main Control Valve → Center Swivel Joint → Left and Right Travel Motors → Return Line → Center Swivel Joint → Hydraulic Tank

The travel motors convert hydraulic energy into rotational power. The final drive reduction units then reduce speed and increase torque, allowing the tracks to move the machine.

For this reason, an excavator travel problem does not automatically mean that the travel motor is faulty. Problems with the main pump, pilot system, main control valve, center swivel joint, travel motor, or final drive can all affect travel performance.

2.Main Components of an Excavator Travel System

A single-side travel circuit normally includes:

• main hydraulic pump
• pilot control system
• main control valve
• center swivel joint
• travel balance valve
• travel relief valve
• travel speed change valve
• travel motor
• brake mechanism
• final drive reduction

Depending on the excavator model, the travel motor may also contain:

• Brake piston
• Two-speed control mechanism
• Swash plate or piston assembly
• Make-up valve
• Anti-cavitation valve
• Overload relief valve

These components work together to control travel direction, travel speed, braking, and torque.

3.Excavator Travel Motor Problems &what Causes Weak Travel on One Side?

Weak travel on one side is one of the most common excavator travel problems.

If only the left or right side is weak while the other side operates normally, the fault is usually located in the affected travel circuit rather than in the entire hydraulic system.

3.1 Internal Leakage in the Center Swivel Joint

The center swivel joint connects the hydraulic system in the upper structure with the travel system in the undercarriage.

Because the upper structure rotates while the travel motors remain in the lower frame, hydraulic oil must pass through the center swivel joint to reach the left and right travel motors.

Inside the swivel joint are several separate oil passages. Seals keep these circuits isolated from each other.

When the seals become worn, hardened, or damaged, internal leakage may occur.

For example, part of the high-pressure oil intended for the left travel motor may leak into a return circuit or another low-pressure passage.

This causes:

Pressure loss → Reduced motor torque → Weak travel

Severe internal leakage may also cause uneven travel or tracking to one side.

3.2 Excavator Travel Motor Problems & Internal Leakage or Failure of the Travel Motor

As the travel motor wears, components such as the pistons, cylinder block, and valve plate may develop excessive clearances.

High-pressure oil can then leak internally instead of producing useful motor torque.

Typical symptoms include:

• Weak travel on one side
• Reduced climbing ability
• Worse performance after the hydraulic oil becomes hot
• Excessive case drain flow

In addition to the rotating group, faults in the balance valve, relief valve, or two-speed mechanism can also cause pressure loss.

3.3 Insufficient Main Pump Pressure or Flow

A worn or internally leaking main hydraulic pump can also cause weak travel.

However, if only one side is weak while the boom, arm, bucket, and opposite travel side operate normally, the main pump should not be blamed immediately.

The pump-to-circuit relationship must be checked according to the specific excavator model.

Possible main pump problems include:

• Internal pump wear
• Pump regulator failure
• Proportional solenoid malfunction
• Incorrect pump control pressure
• Swash plate control mechanism sticking

3.4 Internal Leakage or Restricted Movement in the Main Control Valve

The main control valve is the hydraulic control center of the excavator.

After long operating hours, contamination or normal wear may damage the spool or valve bore.

If the travel spool becomes excessively worn, internal leakage can reduce the pressure and flow supplied to the travel motor.

If the spool sticks or cannot move fully, the travel circuit may also receive insufficient oil.

3.5 Low Pilot Pressure

The travel pedals or levers do not directly control the main hydraulic flow. Instead, pilot pressure moves the travel spool inside the main control valve.

If the travel pilot valve leaks internally, sticks, or produces insufficient pilot pressure, the main spool may not open fully.

The result is:

Insufficient spool opening → Reduced travel flow → Slow or weak travel

Comparing left and right secondary pilot pressures is an effective diagnostic method.

3.6 Travel High/Low Speed Switching Failure

Most excavators have two travel speed modes:

Low speed, often called “turtle mode,” is used for climbing, heavy loads, and rough ground.

High speed, often called “rabbit mode,” is used for faster movement on relatively flat surfaces.

The two-speed system usually works by changing the displacement of the travel motor.

In general:

Low-speed mode uses larger motor displacement, producing lower speed but higher torque.

High-speed mode uses smaller motor displacement, producing higher speed but lower available torque.

If the motor remains stuck in high-speed, small-displacement mode, the excavator may feel weak under heavy load or while climbing.

If it remains in low-speed, large-displacement mode, the most obvious symptom is usually slow travel speed.

4.Why Does the Engine Lug During Travel motor?

Engine lugging during travel means the engine speed drops noticeably when the operator commands travel. The engine may sound heavily loaded and, in severe cases, may stall.

This normally indicates excessive hydraulic or mechanical load.

4.1 Excavator Travel Motor Reduction Unit Failure

A travel motor rotates at relatively high speed, so a planetary reduction unit is used to reduce speed and increase torque.

If the final drive develops problems such as:

• Damaged bearings
• Broken planetary gears
• Poor gear engagement
• Low or contaminated gear oil
• Internal mechanical seizure

the mechanical resistance can increase significantly.

The travel motor then requires more hydraulic pressure to turn the final drive, increasing load on the hydraulic pump and engine.

This can cause the engine to lug.

4.2 Tracks Adjusted Too Tight

Excessive track tension is another commonly overlooked cause.

When the tracks are too tight, friction increases between the sprocket, carrier rollers, track rollers, idler, and track chain.

This increases travel resistance, especially when turning or climbing.

Track tension should therefore be checked whenever the engine lugs during travel.

4.3 Frozen Tracks or Foreign Material in the Undercarriage

This is especially important in cold climates.

Mud and water left on the tracks after operation may freeze overnight, locking the undercarriage.

Rocks, steel bars, wood, or other debris may also become trapped between the track and undercarriage components.

If the operator continues forcing the travel system, engine lugging may occur and the travel motor or final drive may be damaged.

4.4 Main Pump Power Control Failure

If the main pump regulator or power control system fails, the pump may maintain excessive displacement even when engine load is already too high.

This can overload the engine.

If the machine lugs not only during travel but also during boom lifting, arm operation, or combined hydraulic functions, the following should be checked:

• Engine power output
• Main pump regulator
• Pump power control solenoid
• Engine-to-pump power matching

5.What Causes Sticking or Intermittent Travel?

Travel sticking usually means the machine does not move smoothly. It may move, stop, move again, or change speed unexpectedly.

5.1 Unstable Pilot Valve Operation

If the travel pilot valve spool sticks or becomes worn, the secondary pilot pressure may fluctuate.

The travel spool in the main control valve then moves inconsistently, causing unstable hydraulic flow.

This can make the excavator travel intermittently.

5.2 Mechanical Failure in the Final Drive

Damage to gears, bearings, or the planetary carrier can cause periodic mechanical binding.

Typical signs may include:

• Abnormal mechanical noise
• Grinding sounds
• Metal particles in final drive oil
• Repeated sticking at certain rotational positions

5.3 Excavator Travel Motor Control Valve Failure

Faults in the travel motor balance valve, relief valve, make-up valve, or two-speed control mechanism can prevent smooth motor operation.

Valve sticking is especially common when the hydraulic system is contaminated.

6.What Causes Jerking or Surging During Travel?

Travel jerking is similar to sticking, but the excavator usually continues moving while speed or pulling force repeatedly changes.

6.1 Unstable Main Pump Displacement Control

Modern excavators use variable-displacement piston pumps that continuously adjust swash plate angle according to load, control pressure, and controller signals.

If the following components malfunction:

• Pump regulator
• Proportional solenoid
• Control pressure circuit
• Pressure sensor
• Electronic control signal

the pump displacement may fluctuate.

This produces:Pump flow fluctuation → Travel motor speed fluctuation → Jerking or surging

6.2 Unstable Travel Relief Valve Operation

Relief valves limit the maximum pressure in the hydraulic circuit.

If the spring is fatigued, the spool is worn, or contamination causes sticking, the relief pressure may become unstable.

The valve may repeatedly:

Open → Close → Open again

This causes pressure fluctuation and may produce a noticeable jerking sensation during travel.

6.3 Travel Motor Internal Control Problems

On variable-displacement travel motors, faults in the swash plate, servo piston, or two-speed mechanism can cause unstable motor displacement.

Other symptoms may include:

• Abnormal high-speed mode
• Abnormal low-speed mode
• Uneven travel speed on one side
• Problems becoming worse after warm-up

7.Why Is Excavator Travel Speed Slow?

If both tracks operate normally but the overall travel speed is noticeably lower than expected, the following areas should be checked.

7.1 High-Speed Mode Cannot Engage

A two-speed system fault is a common cause of slow travel.

Problems may involve:

• Travel speed solenoid
• Two-speed control valve
• Pilot control circuit
• Travel motor servo mechanism
• Electrical switch or wiring

Even if the monitor shows high-speed mode, the travel motor may still remain in low-speed, large-displacement mode.

7.2 Insufficient Main Pump Flow

Travel speed depends heavily on the amount of oil supplied to the travel motor.

If the main pump is badly worn, the regulator is faulty, or the swash plate cannot reach its required maximum angle, pump output flow may be too low.

In this case, other machine functions such as boom and arm operation may also become slower.

7.3 Insufficient Pilot Pressure

If pilot pressure is too low, the travel spool in the main control valve may not open fully.

Even if the main pump is healthy, the travel motor cannot receive enough flow.

The result is:

Travel works, but maximum speed cannot be reached.

The secondary travel pilot pressure should be checked with the travel lever or pedal fully operated.

7.4 Insufficient Travel Spool Opening in the Main Control Valve

Spool wear, sticking, spring problems, or internal contamination may limit spool travel.

This creates excessive restriction in the travel circuit and reduces flow.

Excessive hydraulic oil temperature may also be observed.

7.5 Excessive Internal Leakage in the Travel Motor

When a travel motor is badly worn, part of the supplied oil leaks internally instead of producing motor rotation.

As a result, even with normal pump flow, the actual motor speed may decrease.

8.How to Troubleshoot Excavator Travel Motor Problems

When an excavator develops a travel problem, it is usually not a good idea to immediately remove the travel motor or replace the hydraulic pump.

A better troubleshooting process is:

Determine whether the problem affects one side or both sides → Decide whether the fault is hydraulic or mechanical → Compare left and right pressures → Check pilot pressure → Inspect the center swivel joint → Check the main control valve → Inspect the travel motor and final drive

Some useful diagnostic clues are:

If only one side is weak:
Compare left and right travel pressure, pilot pressure, center swivel leakage, and travel motor case drain flow.

If both sides are slow:
Check engine speed, main pump flow, pump control system, and high/low travel speed control.

If the engine lugs only during travel:
Check track tension, final drive condition, and mechanical resistance in the travel system.

If the engine lugs during all hydraulic operations:
Check engine power output and main pump power control.

This type of step-by-step diagnosis is far more effective than replacing parts without testing.

9. Conclusion

Although the excavator ultimately moves through its left and right travel motors, the complete travel system includes the main hydraulic pump, pilot system, main control valve, center swivel joint, travel control valves, travel motors, and final drive reduction units.

Therefore, symptoms such as weak travel on one side, engine lugging, sticking, jerking, or slow travel speed should not automatically be blamed on the travel motor.

The most effective troubleshooting method is to identify the exact symptom, compare both travel circuits, and perform pressure, flow, pilot pressure, leakage, and mechanical resistance tests.

Before replacing expensive components such as the hydraulic pump, travel motor, center swivel joint, or main control valve, hydraulic pressure and flow testing should be carried out whenever possible.

FAQ

1.Why is my excavator weak on one side when traveling?

Weak travel on one side is often caused by internal leakage in the center swivel joint, a worn travel motor, low pilot pressure, a sticking travel spool in the main control valve, or a problem with the hydraulic pump circuit supplying that side.

2.Why does my excavator travel slowly?

Slow travel may be caused by a high/low travel speed switching failure, insufficient main pump flow, low pilot pressure, restricted movement of the travel spool, or excessive internal leakage in the travel motor.

3.Why does the engine bog down when the excavator travels?

Engine bogging during travel usually indicates excessive hydraulic or mechanical load. Common causes include an overloaded or damaged final drive, tracks that are too tight, debris or ice blocking the undercarriage, or incorrect main pump power control.

4.Can a bad travel motor cause weak excavator travel?

Yes. Internal wear in the pistons, cylinder block, valve plate, relief valves, or balance valve can reduce hydraulic efficiency and cause weak travel, slow speed, or poor climbing performance.

5.Can the center swivel joint cause excavator travel problems?

Yes. Worn seals inside the center swivel joint can allow high-pressure oil to leak between hydraulic passages. This may cause weak travel on one side, uneven tracking, pressure loss, or reduced travel performance.

6.Why does my excavator jerk or surge while traveling?

Jerking or surging may be caused by unstable main pump displacement control, a sticking relief valve, fluctuating pilot pressure, or faults in the travel motor’s swash plate, servo piston, or two-speed mechanism.

7.Why does my excavator travel in low speed only?

If the machine cannot switch into high-speed travel, check the travel speed solenoid, two-speed control valve, pilot circuit, electrical wiring, travel speed switch, and the travel motor displacement control mechanism.

8.How can I tell whether the problem is the hydraulic pump or the travel motor?

If both travel sides and other hydraulic functions are weak, the main pump or pump control system may be the cause. If only one side is weak while other functions work normally, the fault is more likely in the travel motor, swivel joint, main control valve, or the hydraulic circuit for that side.

9.Can tight tracks cause excavator travel problems?

Yes. Tracks that are adjusted too tight increase rolling resistance and place additional load on the travel motors, final drives, and engine. This can cause slow travel, engine lugging, excessive wear, and higher fuel consumption.

10.What should I check first when an excavator has a travel problem?

First determine whether the problem affects one side or both sides. Then check track condition, travel speed mode, pilot pressure, travel pressure, main pump flow, center swivel leakage, travel motor case drain flow, and final drive condition.

11.Should I replace the travel motor immediately if the excavator is weak?

No. Weak travel does not always mean the travel motor is damaged. Pressure, flow, pilot pressure, leakage, and mechanical resistance should be tested before replacing expensive components.

12.Why does an excavator travel normally when cold but become weak when hot?

This often indicates internal hydraulic leakage. As hydraulic oil temperature rises and viscosity decreases, leakage through worn pump, valve, swivel joint, or travel motor components becomes more noticeable.

13.Can dirty hydraulic oil cause travel system problems?

Yes. Contaminated hydraulic oil can cause valve spools to stick, accelerate pump and motor wear, damage seals, and create unstable hydraulic pressure, leading to slow, weak, or jerky travel.

14.What pressure tests are useful for diagnosing excavator travel faults?

Useful tests include main pump pressure, left and right travel pressure, pilot pressure, relief pressure, travel motor case drain flow, and pump flow. Actual test specifications should always be compared with the manufacturer’s service manual.