How to Drill and Tap a Drain Plug Differential

Changing the gear oil in a differential can be quite the task without a drain plug. Draining the gear oil would include pumping it out like in a boat engine or completely removing the heavy center section itself. Unfortunately, draining the gear oil does not let all the fluid out and can lead to heavy contaminates left over in the new oil. Removing the center section can be difficult. It involves removing, resealing and reinstalling it. An alternative to this process is drilling and tapping a drain plug into the differential housing.

Step 1 - The Hole

Drill a 21/64th inch hole in the bottom of the rear end housing. This is in between the gas tank and the drive shaft. Make sure you drill at the passenger side at the middle of the bottom of the housing.

Step 2 - Breaking Through

Once the drill breaks through the housing, the oil will begin to drain. Catch this oil in the oil catch basin.  As the oil drains, it will take the metal shavings with it. Use a magnet to make sure that all the metal shavings are removed from the differential housing.

Step 3 - Differential Drain Plug Pipe Tap

In addition to a metal pipe plug, use a drill bit or 1/8 inch pipe tap in order to tap the hole. You can purchase all of these items at an auto parts store or a hardware store. The tap is tapered. This means that it will cut larger diameter threads the deeper that you go. Back the tap out frequently in order to remove as many metal shavings as possible. In addition, use the magnet to remove the shavings as you go.

Step 4 - Torque

Do not use extreme torque to seal the pipe plug properly. This means that you do not have to add a lot of force to turn it. To add special protection to your housing and the plug that you just installed, a magnetic plug can be installed. Use a socket head type plug to finish.

Step 5 - Additives

At this point, you can add gear oil and Sure Grip additive to ensure the best quality plug.

Step 6 - Precautions

Make sure you are careful to lift your car on level surfaces and as level as possible after this procedure.

Step 7 - Fill Plug

With a wrench, reinstall the fill plug.

Step 8 - Driving

To ensure that your work does not leak, the final step is to drive your car.

Once the drain plug is installed, you can be assured that checking your vital fluids is much more accessible and thus, easier than before.