Final drive troubleshooting – 8 common issues

27.02.2023

Drive motors are undoubtedly one of the most important elements in tracked machines – their failure involves costly downtimes and in extreme cases even total immobilization of equipment in the field. In this post, we will look at the most common causes of final drive failure – this knowledge will enable you to avoid inappropriate operating practices and significantly extend the lifespan of your drive motors.

What is a final drive?

A final drive, also known as drive reducer/travel motor, is one of the final components of the drive unit. The use of a final drive allows the torque to be increased (i.e. the revs are slowed down) only at the drive wheels, which not only allows easier traversing of difficult terrain, but also relieves the strain on the preceding drive components. Final drives are commonly used in various construction equipment (especially tracked excavators) and utility vehicles designed for use in rough terrain.

Generally speaking, a final drive is composed of two systems – hydro motor and mechanical gearbox (commonly a satellite sprocket box). These are very precisely made elements that are excellent at transferring propulsion. With correct use and regular maintenance, the final drive will operate faultlessly for many years.

Most common issues

As any other machine parts, a final drive can malfunction. Here are 8 of the most commonly occurring issues with it:

Oil leaking from gearbox cover plate

Gear oil is an essential part of smooth final drive work – without it, the gears would overheat and wear out quickly. So if you notice there’s a leak, you should investigate the matter as fast as possible.

When there is a leakage from underneath the gearbox cover plate, there are two most probable causes – either the cover is distorted, or there’s a built-up pressure in the gearbox. The first one is straightforward to deal with – all you have to do is replace the damaged cover plate. The other is far more complicated and dangerous – with a prolonged build-up, the pressure can rip apart the gearbox. So if you suspect there’s excessive pressure, contact the service centre immediately.

Oil leaking from the ring gear

This issue is rather straightforward – it’s probably caused by a worn-out/damaged floating seal. Simply get it replaced and everything should work as intended.

Gearbox oil level too high

Too much oil is as bad as not enough gear oil. Due to the excessive heat produced by working gears, the oil expands its volume and starts to push out the seals, causing leaks and hydraulic pressure build-up. So you should never pour oil all the way to the cap.

If you’ve been pouring the proper amount of oil and yet, its level in the gearbox is too high, the problem might lie in the worn out bearings/seal between the final drive motor and the gearbox. In this case, simply replace them and the oil level should get back to normal.

Excessive noise

Heavy equipment is undeniably loud. Despite that, the operator should be familiar with all the sounds it emits during work. Strange noises coming from a final drive are a clear sign there’s something wrong with it. You should never ignore such a noise – when left unchecked, simple issues that would take just a few minutes to fix can transform into serious and costly problems.

There are 3 main issues that can generate excessive noises:

  • Insufficient oil level in gearbox – this is most often caused by leaks or lack of final drive maintenance. If this persists despite pouring more oil, you should overhaul the gearbox/motor;
  • Worn-out bearings/gears – again this is most likely caused by the lack of maintenance or reaching the final drive’s planned service life. In this case, you should replace the travel motor with a new one;
  • Impurities in the oil – this is also a consequence of neglecting maintenance – metal swarf from improperly oiled gears end up in the oil, which causes increased friction that grinds off even more material. The solution here is disassembling the motor and gearbox, cleaning them up and replacing the worn-out elements. Or getting a brand-new travel motor.

Hot gearbox casing/ring cover plate

As with the leakages, this can have 2 causes of varying severity. On one side, it could be a simple matter of low oil level (which can be remedied by adding more), on the other – worn bearings, which require an overhaul of the gearbox.

Difficulty in terrain-climbing

When your machine (e.g. excavator) has trouble in traversing rough terrain, it’s often cased by one of these 3:

  • Lack of power – this is most likely due to low hydraulic pressure in the hydro motor, so check it first. Subsequently, check hydraulic fluid level and look for leaks. If you can’t find an apparent cause, contact service centre;
  • Excessively worn-out travel motor – the only solution here is getting a replacement;
  • Excessively worn-out gearbox – same as above.

Motor works but gearbox fails to move

Again, we have 3 most possible cases here. First is a broken motor shaft – if that’s the case, both the shaft and the 1st drive gear/sun gear should be replaced. Second – broken drive shaft, which is the only element that needs replacing in this scenario. And last, but definitely not the least – broken sun gear/1st drive gear. Here, replacing the damaged gear should be enough.

Motor idling

Idling in final drive motors can be caused by a broken motor shaft or worn cylinder block/friction plate. Each of these can be remedied by replacing said element.

Repairing a final drive after failure – is it cost effective?

While an early detected failure of the travel motor does not entail high costs (especially if a minor component has to be replaced), for more serious damage, regeneration does not make much sense. For example, the repair of hydro motors, including labour costs, is almost as expensive as a whole new final drive, and there is no guarantee that no further parts will have to be replaced in a short time. Therefore, for major failures, it’s best to buy new final drives straight away – Track Motor shop has all you’ll need. We offer replacement travel motors for tracked excavators from over 50 brands, both worldwide-known and local.

Final drive issues – summary

Most of the final drive problems are caused by negligence in maintenance – almost all serious failures can be avoided, if you pay attention to your equipment and react soon enough. This can save you a lot of time and money, as travel motors are costly to replace. With enough care, your final drive will be working properly for all of its lifespan.

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