Proper gearbox maintenance is key to a long life of your unit. The normal service interval should be 2500 hours or 6 months in most units. As seen in the first picture this unit has been properly maintained, has a good wear pattern, and hasn’t been overheated. Excessive heat or improper lubrication will cause pitting in the teeth. Routine maintenance is important as it removes the old oil that may no longer provide proper lubrication.
Gearbox oil is much like the oil in your vehicle over time and heat cycles it loses its ability to protect the internal parts due to viscosity breakdown. Unlike your vehicle the gearbox doesn’t have a filter to catch the debris so the used oil will have some metal shavings and debris in it. Don’t be too alarmed to see some metal in the used oil. The key is to change the oil a scheduled intervals before it breaks down.
The oil level and type is very critical to the life of the unit. There are many different types of site glasses on the market that may or may not allow you to accurately maintain the proper oil level. The “L” shaped sight glass below is best to allow proper level monitoring. The level indicated on the sight glass is very important. unmarked sight glasses should be marked an inch up the vertical section of the glass. The key is to make sure the oil is at a level slightly above the centerline of the gearbox. That oil level will insure that the gears are submerged under oil which will greatly reduce heat and friction on the gears which result in a longer life. The recommended oil is important as well. It MUST NOT be an EP (extreme pressure) lubricant! As seen in the second picture this brass gear has pitting in the teeth which can indicate an EP additive in the oil used. You can see the degradation of the area over and under the teeth where the gear has been attacked. As opposed to the picture above where the brass gear is neither pitted nor attacked and has a proper wear pattern. It should have a VI (viscosity index) of 90 minimum. An example of an approved lubricant is AGMA #8 Chevron ISO 680 or AGMA #8A Chevron ISO 1000.