DIY: Rear Differential Fluid Flush and Change
Changing out the rear diff fluid can be a little bit intimidating if you've never done it before. The alignment of the holes make it impossible to pour the fluid into the differential if it is mounted onto the car.
What you need:
1 Quart Differential Fluid (We use 75w90 Amsoil Severe Gear in the WRX)
1/2" drive wrench
Vacuum Pump or Siphon Pump
Jack and Stands (depending on how low you are)
*I also had a 1/2 quart of leftover Severe Gear which I used to flush out any residual
Approximate time: 30 minutes
Jack up the car, and get everything prepared
Remove the lower drain plug and let the old fluid drain into the pan (or in this case, an old sand castle pail. Yes, moving does suck because you lose all of your stuff). Inspect the plug for any large metal shavings. It is magnetic, so any residue should be attached to it. Wipe it of clean, then set it aside for later.
Once the fluid is flowing slowly, screw the pump onto the quart of fluid (if you're going to flush out with an open bottle, put the pump on that guy first)
Pump a few ounces (of the old fluid) into the diff and let the fluid flow back out of the drain hole.
Once you are happy with amount of fluid you've drained from the diff, plug up the bottom and pump the fresh quart into the top hole.
Slowly fill the diff until fluid begins to drip out of the top fill hole. Then clean up any fluid that dripped onto the assembly and bolt her back up!