ATVs and UTVs get abused. That is a basic fact of their existence. These machines get dragged through the mud, up the roughest trails and often receive little attention in the maintenance department. A typical 4×4 would be lucky to have the differential and final drive gear oil changed after being drowned in mud and water. For the best results, the differentials and final drive gear assemblies need to be taken apart to be cleaned and inspected.
The differentials need to have their oil levels inspected on a regular basis. The oil should be changed according to the periodic maintenance chart in the service manual or whenever the differential/final gear case has been submerged in water or mud.
If the differential oil has a white tint, that’s a sign of water contamination. While changing the oil is great, the only way to remove all of the moisture contamination is to disassemble the differential and clean the components.
Before disassembling the differential or final drive gear, be prepared to replace oils seals, sealing washers and staked lock nuts. Also, make sure to check the service manual for any special tools that may be required. Often, a special lock nut wrench is needed to take out the pinion gear shaft.
Clean the differential and final gear components. Check the gears, bearings and differential clutch discs for signs of wear and damage. Replace the differential components as needed.
Assemble the final drive gear or differential and check the backlash. The backlash is the amount of free movement between the ring and pinion gears. Check the backlash with a dial gauge. Adjust the shims as needed to make sure the backlash is in specification. Usually, the shims with the ring gear play the biggest role in setting the backlash.
After setting the correct backlash, the gear tooth contact needs to be inspected with a gear marking compound. Apply the contact checking compound to four to five teeth on the pinion gear. Assemble the differential or final drive gear. Hold a gentle drag on the ring gear while turning the pinion gear shaft. Turn the pinion gear shaft three to four turns in the forward direction and the same in the reverse/coast direction.
If the contact is far out of center, the shims need to be changed. Usually the shims with the pinion gear play the biggest role in gear tooth contact. Change the shims a small amount at a time and recheck the tooth contact and backlash. Clean the checking compound from the teeth before each inspection and final assembly.
Reassemble the final drive or differential. Tighten all of the fasteners to the correct torque specification as indicated by the service manual. Be sure to secure the pinion gear shaft lock nut. This may involve staking it or using a thread locking compound.
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