THERE ARE a few extra things a 4X4 needs over a passenger car for maintenance and one of those things is regular differential oil changes.
The 4X4 diff not only has a harder time of it because it spins up more in off-road situations, but it is also often dunked into cold water when hot, and cops dusty conditions up close. All of this means that the diff oil can become contaminated and lose some of its lubricating qualities.
Manufacturers vary with their requirements for diff oil changes, but generally speaking they are in the region of 30,000-40,000km intervals. The type of oil used is important too; limited-slip differentials require a friction additive for their oil, which can be bought separately and added when filling the diff, or bought pre-mixed in the bottle with the diff oil.
Most diff oils are also gearbox oil, although it pays to check exactly what the manufacturer specifies and stick with those recommendations.
Changing diff oil is pretty simple. The only problem is differential gears don’t like contaminants, so attempting a diff oil change on a windy day out on the dirt is not a good idea. Also, it can be difficult to pump the fresh oil in if you don’t have an adequate pump – unlike engine oil or transmission oil, you can’t rely on gravity to feed in the new oil. Some prefer a dedicated gasket to seal up the diff hat while most rely on a good quality silicone sealant. The trick here is to not go crazy with the amount of sealant that is applied to the diff hat.
1. Nothing too tricky needed to tackle this job: diff oil, silastic sealant and an oil pump.
2. Remove diff’s 1/4 inch recessed plug. Most have hexagonal bolt-head or rubber plugs.
3. Then remove the half-inch bolts holding the diff hat on.
4. Use a screwdriver to prise the diff hat off as the old silastic is holding it on firmly.
5. Scrape any silastic remnants from the diff hat with a plastic scraper.
6. Put a clean, lint-free cloth in the diff centre so that debris can’t fall in.
7. Remove the old silastic on the diff housing with your plastic scraper.
8. With the bulk of the old silastic removed, clean up the remainder with wax and grease remover.
9. Apply a bead of silastic to the diff hat. The bead mustn’t be too thick or it’ll go everywhere.
10. Refit the diff hat and hand-tighten the bolts. Then torque those bolts up.
11. Add fresh diff oil to the diff to just below the oil filler hole.
12. Refit the diff filler plug and torque it to specification.