You’ve taken the cover plate off your final drive, and now you're looking at the gears in the planetary hub. How do you know when to replace those gears? In this Shop Talk Blog post, that’s precisely what we are going to discuss: signs that your gears are wearing out.

Importance of Gears

As you probably already know, gears are vital to transmitting power and torque that keeps your machine moving. The gear teeth transfer those loads, and the gear teeth are the primary area where you’ll see the signs of wear. The gears are designed and manufactured to carry those loads, but there is a limit to what they can handle. There are signs you can look for that will indicate gears are reaching the end of their useful life, fortunately.

Worn Gear Teeth

The surface of the gear teeth will wear away over time. If your gear teeth look pointed, that is a sign that it's time for you to replace them. When the gear teeth wear down to a point, they can’t mesh properly and can’t transmit loads effectively. We’ve got an example of that below with a worn drive shaft next to a good drive shaft. While some wear is expected, not enough gear oil or by gear oil that is contaminated will accelerate it.

Bent Gear Teeth

If your gear teeth are bending from the root, that is not a good sign. You may also see a crack at the root of the gear tooth. In extreme cases, the teeth themselves may have broken off. If you see bent gear teeth or missing gear teeth, then it’s time to replace those gears. This type of damage is not a sign of normal wear.  It is the result of very severe gear overloading, which could be caused by either abuse of the machine or (more likely) improper alignment.

Surface Damage

One sign to watch out for with gears is pitting. Pitting is the result of surface fatigue and is going to occur where the gear teeth are coming into contact with each other. You may also see that the surface of the teeth have spots that look polished, abraded, or scuffed. These are also signs of surface damage.

Surface damage is normal for gears that have reached the end of their life, but it can also occur if the gears are overloaded. It takes more than a few instances of overloading to cause this kind of damage prematurely, however. It takes consistent overloading to do this. Another contributor to this kind of wear is either contaminated gear oil or too little gear oil.

Cracking

Cracks in gear teeth usually start at the root of the gear teeth but may also be present at the end of the teeth. Misalignment, overloading, and contaminated gear oil are the typical causes of cracks in your gears. If you see cracks in the gears anywhere, replace them right away.  Cracks can reach a point where they spread at the speed of sound, and the results can be devastating to your final drive gearbox.

Preventing Premature Failure

The best things you can do to prevent premature failure of the gears in your final drive motor is to check and change the gear oil on a regular basis. Keep contamination out of the gear hub by using clean gear oil and replacing seals when they begin to leak. Also, remember that contamination includes gear oil that has degraded through age or overheating. The gear oil can no longer do its job, and excessive wear is going to be the result.

If you need to replace one gear and those gears are typically sold as a set, then replace the set. If one gear in a group fails, it will only be a matter of time before the others fail. Adding a new gear into an older gear set will cause more problems. Finally, if a bearing begins to fail, it can throw other components including drive shafts and gears. Bearing failure can cause some of the more severe types of damage discussed.

Conclusion

If you check and change your gear oil regularly, your gears will last a long time. However, parts do have a limited life. If you see any the signs listed here -- worn or bent gear teeth, pitting, or cracking -- then they’ve reached the end of their useful life and need to be replaced.

Texas Final Drive is your partner in providing new or remanufactured final drive hydraulic motors from a single mini-excavator to a fleet of heavy equipment. Call today so we can find the right final drive or hydraulic component for you, or check out our online store to find your O.E.M. manufacturer brand motor now.