- Socket & Wrench
- Catch Can
- Brake Cleaner
- Safety Glasses
- Gear Oil
- Torque Wrench
On a rear or all-wheel drive car, the rear differential transfers power from the drive shaft to each wheel through a series of gears and axels. The interlocking ring and pinion gears require specific lubrication to rotate smoothly and transfer power efficiently. Here are the tools you’ll need to change your rear differential fluid. Socket and wretch, a catch can, break clean, gloves, glasses, gear oil, torque wrench, and a pump.
To see what your service intervals are from the factory, and in there it will also say what type of oil you should be putting in your rear diff. Matt puts our replacement gear oil outside in the sun. More on why he did that later. Next, he instructs me to remove the fill plug first, for two reasons. Number one, you want to make sure the plug has not seized, and would therefore prevent you from refilling the new gear oil once the old is removed, especially if this is your only car. You’d be stuck because you couldn’t move or drive the car safely with no gear oil.
And number two, you do it so the oil can drain out a bit easier, but you do want to make sure no dirt gets in the exposed hole while it’s draining. Some rear diffs do not have a drain plug like this one here, and require you to remove the cover itself. Consult your manual before you get started. This can be a complicated job. On this particular vehicle, changing the rear diff fluid is similar to replacing engine oil. Remove the lower drain bolt and catch the fluid in a pan or a catch can.
The last few turns of the bolt should be done by hand so that you can avoid dropping the bolt and magnet into the pan full of old oil. I caught a small cup of old gear oil to see the before and after shot at the end of this video, but no need to do it at home. Be sure to properly dispose of the spent fluid, this is toxic and must be disposed of properly. Check your local auto parts store to see if they recycle or can recommend where to go.
Next, clean the bolt which doubles as a magnet. This is designed to catch the metal shavings caused by the gear’s rubbing during regular use, and is perfectly normal. Use brake clean and a clean rag to remove the debris before re-installing with the new crush washer. Hand tightens the bolt at first to avoid cross-threading, then torque to your manufacturer’s suggested torque spec. Next, the gear oil is retrieved from sitting outside in the sun. By heating it up in the sun, it flows a bit easier as it travels through the hose and into the pumpkin. Now place one end of the pump hose into the oil and insert the other end into the fill hole. Pump until suction is created, and oil begins to move from the container. Keep in mind, if your car has positraction or a limited slip differential; a special gear oil additive is needed to keep those extra parts lubricated properly.
Luckily, our gear oil already had the additive mixed in. So how do you know when the rear diff is full without a dipstick like the engine oil, the trani fluid, power steering, or even the brake fluid? Well, the filler plug hole itself is strategically placed at the proper level of where the gear oil needs to be just before it starts to spill out. As you can see, the oil will slowly weep out of the hole, letting you know that the proper level has been met. Tighten your fill bolt, in our case it was 33 foot pounds and double check your work. Wipe the area clean so you can easily spot potential leaks in the future. Clean differential fluid will help reduce friction, aggressive wear, and eventual damage by excessive heat, which you might feel as a vibration
At the very minimum, read your owner’s manual to review the maintenance routine for all your fluids, including the always forgotten rear differential.