Excavators demand meticulous care for optimal functionality. One crucial decision revolves around final drive replacement: should both sides be changed simultaneously? If your machine has a noticeable final drive speed difference, you might be wondering why one track tracks slower than the other, causing the excavator to pull or drift to one side. Here, we dissect the reasons behind this tracking speed difference, focusing on wear uniformity, performance balance, proactive maintenance, and diagnostics.

Why does a final drive speed difference occur?

Normally, a speed difference is barely noticeable when tracking in low speed (1st gear) because the flow rate from the main hydraulic pump is low, and minor volumetric losses are easily compensated. However, when you shift the excavator into high speed (2nd gear), the flow rate increases, and the displacement controls in the travel motors are activated. This is when a tracking speed imbalance usually becomes prominent.

The main causes of speed differences between two final drive motors include:

• Mixing old and new motors: Installing a brand-new final drive on one side while keeping a worn motor on the other creates an efficiency mismatch. The older motor has wider internal clearances and lower volumetric efficiency, resulting in less rotational speed under pressure.
• Different motor brands or displacement ratios: Different manufacturers (OEM vs. aftermarket brands) use slightly different displacement ratios and gear reductions. Even a minor deviation in design will cause one track to rotate faster.
• Hydraulic system wear: An imbalance in flow rate from the excavator’s control valve, worn rotary manifold (swivel joint) seals, or wear in one section of the main hydraulic pump can restrict oil flow to one travel motor.

Why you should replace final drives in pairs

To ensure peak excavator performance and prevent uneven tracking, we highly recommend replacing both final drives at the same time. While it represents a larger upfront investment, it is a strategic decision that offers long-term benefits:

1. Wear Uniformity

Both travel motors operate under the exact same terrain, load, and working conditions. If one motor has failed or is severely worn, the other side is typically close to its end-of-life. Changing both ensures uniform wear, prolonging the overall longevity of your excavator’s undercarriage.

2. Balanced Performance

A balanced track speed is a cornerstone of safe and stable machine operation. Straight tracking is critical for maneuverability, operator comfort, and precision grading. Speed imbalances stress the track chains and sprocket teeth, leading to accelerated undercarriage wear.

3. Proactive Maintenance and Cost Efficiency

Addressing both travel motors at the same time reduces unexpected downtime, shipping fees, and labor costs. Doing the job once instead of twice saves valuable mechanics’ hours and helps avoid subsequent project delays.

How to identify and maintain your travel motors

Before purchasing replacement parts, you must identify your existing setup correctly. You can read our detailed guide on how to measure a final drive correctly to gather the required bolt hole diameters and sprocket tooth counts. Regular oil changes and inspection are also vital to keep your drive in peak shape—refer to our walkthrough on how to maintain a final drive to prevent early failures.

If you observe metal flakes in the gear oil or notice a complete loss of power on one side, you may be facing the typical signs your final drive is in bad condition. In such cases, trying to replace a final drive immediately is the safest way to avoid further damage to the hydraulic loop.

For more technical details, you can browse the Mecatra blog overview to access resources on what is a final drive, hydraulic main pumps for excavators, and swing devices for excavators.

Need a quote for replacement motors? Use the request form below to submit your machine model, and our technical team in Horsens, Denmark will get back to you within 1-3 business hours.