Causes of intermittent movement of the travel assembly and overall machine deviation

  In the daily operation of excavators, the travel system plays a crucial role in equipment movement, site relocation, and power output under complex working conditions. Whether in mining, earthmoving, or road construction, stable and reliable travel performance is a fundamental guarantee of construction efficiency.

  However, many users frequently encounter problems such as the excavator's travel speed fluctuating, intermittent movement, or even automatic left or right deviation during straight-line travel. These problems may seem to only affect the user experience, but they often indicate abnormalities in the travel, hydraulic, or transmission systems. If ignored for a long time, this will not only accelerate component wear but may also lead to serious damage to the travel assembly, increasing maintenance costs and downtime.

  So, why does the travel assembly exhibit intermittent movement? Why does the excavator veer off course? Below, we will analyze this in detail from both mechanical and hydraulic perspectives.

What is Intermittent Travel❓

Intermittent travel refers to the excavator's inability to maintain a continuous and stable power output during forward or backward movement, resulting in intermittent pauses, sudden deceleration, or brief loss of driving force. Common symptoms include:

Sudden pauses for several seconds during movement, followed by normal operation;

Discontinuous track rotation, resulting in a jerking sensation;

Significantly insufficient power when going uphill;

The malfunction is more pronounced when the machine is warm than when it is cold;

Abnormal noise or vibration during movement.

These malfunctions are often not caused by a single component failure, but rather by the combined effect of multiple systems.

Common causes of intermittent movement in the travel assembly:

1. Severe internal wear of the travel motor

The travel motor is the core power component of the travel system. Its main function is to convert hydraulic energy into mechanical energy to drive the reducer and tracks.When the travel motor is under high load for a long time, key internal components such as the plunger, auxiliary distributor plate, and swashplate will gradually wear down.

Wearing may lead to:

Increased internal leakage;
Decreased output pressure;
Insufficient torque;
Unstable power output.

Therefore, the equipment may experience sudden changes in speed, intermittent movement, etc. If this is accompanied by motor overheating, abnormal noise, or oil leakage, the internal wear of the travel motor needs to be thoroughly checked.

2. Damaged Gears in the Travel Reducer

The travel reducer is responsible for reducing speed and amplifying torque. Its internal components mainly consist of a sun gear, planetary gears, and an internal gear ring. When the reducer is chronically short of oil, poorly lubricated, or subjected to excessive impact, it may lead to:

Gear wear;
Gear surface peeling;
Missing or broken teeth;

Power transmission will be interrupted. Common symptoms include:

Sudden jerking during movement;
Smooth track rotation;
Clicking or metallic clanging sounds; The fault is more pronounced under heavy loads.

In severe cases, it may even cause the equipment to become completely unable to move.

3. Damaged Bearings in the Travel Assembly

Bearings play a crucial role in supporting and positioning the travel assembly. If the bearings are worn or the cages are damaged, it will lead to:

Output shaft wobble;
Poor gear meshing;
Discontinuous power transmission;

This will cause jerking, abnormal noises, and even oil leaks.

In many cases, users only replace the oil seal after discovering an oil leak, but the real problem is that the internal bearings are already damaged.

4. Insufficient Hydraulic Pump Oil Supply

The hydraulic pump is the power source of the entire hydraulic system. If the hydraulic pump experiences:

plunger wear;
distributor plate wear;
cavitation;
reduced output flow;

insufficient flow and pressure received by the travel motor, leading to unstable power. Common manifestations include:

normal operation when cold, weak operation when warm;
significantly reduced travel speed;
and simultaneously affecting the operation of the slewing and working devices.

Therefore, the working status of the hydraulic pump should not be ignored when checking for travel malfunctions.

5. Hydraulic Circuit Faults

A problem in any part of the hydraulic system can affect travel performance. For example:

insufficient hydraulic oil;
severe hydraulic oil contamination;
clogged hydraulic filter;
air leaks in the pipeline;

all of these will cause unstable oil supply. When hydraulic oil cannot be continuously and stably delivered to the travel motor, the equipment will experience intermittent stalls.

6. Internal Leakage in the Center Rotary Joint

The center rotary joint is located at the center of the connection between the upper and lower frames and is a crucial channel for delivering hydraulic oil to the travel system. When internal seals wear down, hydraulic oil leakage can occur. Common symptoms include:

Weak movement;
One track speed noticeably slower;
Intermittent movement;
Machine deviation.

Especially for older equipment, the center rotary joint is often an easily overlooked point of failure.

Why do excavators sometimes deviate from their straight path❓

Deviation refers to the equipment automatically veering to the left or right while moving in a straight line, requiring the operator to constantly adjust the direction to maintain a straight line. Although it seems like a simple problem, it often involves multiple components such as the hydraulic system, mechanical transmission system, and chassis system.

Main causes of machine deviation:

1. Performance differences between the left and right travel motors

If the left and right travel motors are worn at different rates, it will lead to inconsistent output torque. For example:

The left motor is normal;
The right motor is severely worn;

Then the right-side driving force is weaker, and the equipment will automatically drift to the right. This is one of the most common causes of deviation in actual maintenance.

2. Uneven flow distribution by the main control valve

The main control valve is responsible for distributing hydraulic oil to the left and right travel motors. When the valve core is worn or stuck:

One side will have excessive flow; the other side will have insufficient flow. Even if both motors are functioning normally, this will cause different track speeds, leading to track deviation.

3. Worn Travel Reducer

If the wear on the left and right reducers differs, the output efficiency will differ. When the gears or bearings inside one reducer are severely worn:

Output torque decreases;

Energy loss increases;

Ultimately causing the equipment to drift towards the faulty side.

4. Inconsistent Track Tension

This is the easiest problem to check but also the easiest to overlook. When the tension of the left and right tracks differs significantly:

The side that is too tight will experience increased resistance; The side that is too loose will experience decreased resistance;

The equipment will naturally drift towards the side with greater resistance. Therefore, before checking complex hydraulic faults, it is recommended to check whether the track tension meets the standard.

5. Worn Chassis Components

If the following components in the chassis system—

drive wheels;
idler wheels;
track rollers;
track rollers—are severely worn, it will also affect the track's running trajectory. If left unaddressed for a long time, this can also lead to misalignment.

How to quickly troubleshoot❓

When equipment experiences intermittent movement or misalignment, check the following in order:

Check if the track tension is consistent;
Check the hydraulic oil level and condition;
Check if the hydraulic filter is clogged;
Test the pressure of the left and right travel motors;
Check for internal leakage in the center slewing joint;
Check the condition of the gears and bearings inside the reducer;
Check the operation of the main control valve and hydraulic pump.

Troubleshooting in order of simplicity to complexity often leads to a faster identification of the root cause of the problem.

Conclusion

  Intermittent movement of the travel assembly and overall machine misalignment are common excavator malfunctions, potentially involving multiple critical components such as the travel motor, reducer, bearings, hydraulic pump, main control valve, and center slewing joint. Timely detection and targeted inspection not only prevent the problem from escalating but also effectively extend the service life of the travel system.

For equipment that operates in mines, quarries, and under heavy loads for extended periods, regularly inspecting the walking system and promptly replacing lubricating oil and worn parts are crucial measures to ensure stable operation and reduce maintenance costs.