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Do-It-Yourself Projects
Replacing Axle Seals
By Mike Bumbeck/
Printable version
Degree of DifficultyDifficult
Estimated Time180 minutes
180 minutes
As much as you try to ignore it, that pesky spot of oil on the driveway isn't getting any smaller. Sure, you can put a tray of some sort under the car, use cat litter, or some type of space age polymers to sop up the drips. You can even try parking in a different spot, but the oil will keep on dripping. While oil spots on the driveway are certainly a nuisance, the fact that the oil is no longer in the engine crankcase or transmission can pose a real problem for your transmission and your budget.
Replacing Axle Seals
The automobile contains a number of fluids that should all stay where they're supposed to be. Oil spots, coolant leaks, mysterious drips, and other signs of fluids leaving their rightful places inside the automobile are telltale signs that you should pay attention to. One of these parts crying for care by leaking gear oil all over the driveway or garage floor is an axle seal. Sometimes, oil on the outside of the case where the axles enter will be the only indication of a problem. A surefire way to determine if the leaking oil in question is engine or gear oil is to follow your nose. Gear oil has a unique, rotten egg type of smell.

Gnashing and Shifting
Gear oil has this unique smell for a reason. The inside of a manual transmission, transaxle, transfer case, or differential of an automobile is a truly harsh environment. Gear oil is manufactured specifically to handle the gnashing and spinning of gears as you shift from First to Second, from Third to Fourth, and so on.

Gear oil is different than motor oil in a number of ways. One is that it is much thicker, possessing a higher viscosity. This viscosity helps the oil stick to the gears as they gnash and spin. The other difference is that gear oil is designed to provide lubrication in the high shock conditions that accompany the meshing and occasional mashing or grinding of gears. The chemical compounds in the oil often contain sulfur, which also give the gear oil its unique, expired egg smell. The thickness, combined with the special chemical compounds of the gear oil, lubricates and cushions the gears as they shift. The gear oil is crucial to achieving the ultimate goal of the transmission, transaxle, differential or transfer case—to transmit the power of the engine through the axles and the wheels and then down to the ground--and managing to do it all again, day after day.

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