If your final drive is hot to the touch or steams when it is wet, that indicates some possible issues that need to be addressed. In this Shop Talk blog post, we are going to talk about potential causes for an overheating gearbox on a final drive.

When your gearbox is overheating, the first thing to check is the gear oil level. When the oil level falls too low to adequately lubricate the components within the planetary hub (gears, bearings, etc.), the result is increased friction between contacting parts. This increase in friction leads to a build-up of heat. If you find the gear oil level is low, top it off but be aware that there may very well be a leak in your final drive if you have to repeatedly top it off.

Hydraulic Fluid

If the gear oil level is sufficient, the next item to check should be the hydraulic fluid. An overheating gearbox can occur if the hydraulic fluid is too hot. In fact, overheating is actually one of the most common issues that occur in hydraulic systems. The hydraulic fluid should be no more than 180°F. In the hydraulic fluid is hotter than that, the problem isn't caused by your final drive; it's an issue with the hydraulics. You will need to check the hydraulic fluid cooler and the hydraulic system.

Brakes

Is the gear oil level is all right and the hydraulic fluid temperature is acceptable, then your next step will be to check the brakes. If the brakes are not releasing properly, then there is going to be significant increase in friction and heat. Think of what would happen with your car if you try to ride the brake all the time. You will need to check the operating pressure on the brake and check the piston seals.

You can check your machine service manual for information on how to check the brake pressure. A lack of brake pressure is usually going to be the result of a weak charge pump or a brake seal that isn’t holding the pressure anymore.

Bearings

If everything else checks out, then the source of overheating is most likely going to be worn-out bearings. If this is the case, the bearings will need to be replaced before a catastrophic (and expensive) failure takes place. Keep in mind that bearings do have a finite service life which can be significantly reduced if the gear oil isn’t properly checked in changed in the final drive. When bearings begin to fail, the results can be very expensive. The picture below shows how a failed bearing caused irreparable damage to a final drive that came into our shop.

Conclusion

If your final drive gearbox is overheating, you need to check the gear oil level, hydraulic fluid temperature, and brakes. If the problems doesn’t lie in any of these areas, it is most likely the result of bearings that need to replaced ASAP. Finally, if you don't own one, it’s always a good idea to purchase a service manual for your machine for information on proper and routine maintenance.