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How to Install a Torque Converter Drain Plug

by Francis Walsh

Building engine performance for use in a sanctioned automotive event demands that equipment be powerful and easy to tune. Rebuilding a transmission will include a fluid drain from both the torque converter and transmission housing. The job can be messy because there are no drain plugs to allow the fluid to drain. Install a torque converter drain plug to remove the oil that sits inside the converter even after draining the transmission pan.

Secure the torque converter in a bench vise with the location of the torque converter drain plug pointed downward. It is recommended that the drain plug be installed on the outer edge of the converter in the band that encircles the unit. Point that location at the five thirty position, and firmly secure the converter in the vice. Use towels or rubber to place in between the bench vice and the converter to protect the outer skin of the converter.

Insert a 1/2 inch NPT drill bit into an electric drill. The drill bit will make an opening that then can be tapped to fit the 1/2 inch NPT drain plug. Begin drilling at the location for the new torque converter drain plug by using the drill at low speed until the bit makes its first cuts into the converter's outer band. Once a mark has been made by the drill, you can begin to speed up the RPM of the drill to cut through more quickly. The drill and drill bit should be pointed upward into the converter to allow for all the metal shavings to fall free of the converter. These shavings must be prevented from entering the converter.

Stop drilling once the tip of the drill bit has broken through to the inside of the torque converter housing. The cuts now must be made slowly, as you open the hole into the converter. Sharp drill bits will cut ribbons of metal when rotated slowly. It is important to keep track of every piece of metal as you drill, and tap the hole for a torque converter drain plug. Use a small retractable magnet to reach inside the converter to attract any metal pieces that may lie on the inside of the housing near the hole.

Insert the 1/2 inch NPT tap into a tap handle, and lubricate with a small amount of cutting oil. Place the tip of the tap into the hole in the side of the converter. With the tap held in a vertical position from the hole, begin to twist the tap into the hole. Turn clockwise, until the tap can be felt to be cutting, then back off. The process of tapping a hole involves firm turns clockwise to cut, and then counterclockwise to remove the debris. Control the amount of metal shavings that can fall into the converter by using the magnet to clean the work area around the hole. The small shavings will collect in the cutting oil, and can be pulled from the converter using the magnet. Tap the hole deep enough to allow for a torque converter drain plug to be threaded at least half way for 1/2 inch NPT drain plugs.

Place two drops of Loctite on the 1/2 inch NPT drain plug, and thread into the newly threaded torque converter drain plug hole. Turn counterclockwise until tight, or until the top of the drain plug is even with the outside edge of the torque converter. Never thread the drain plug so deep that the loosening adapter is beneath the outside edge of the torque converter.

Tip

  • Balance the torque converter on a converter balancing machine, or bring the converter to a transmission rebuild company. By adding a torque converter drain plug, you will have changed the balanced weight of the unit. Rebalancing involves spinning the converter on a table, and the offset weight is measured by a computer. View a torque converter balance at ATI Racing.

Warning

  • Without a proper balance after installing a torque converter drain plug, an offset in weight can damage internal transmission parts and gears. Any alterations in gear, converter and pump weights can affect handling.

Items you will need

About the Author

Francis Walsh has been working as a freelance writer since 2003. He has contributed to websites such as Shave, Autogeek and Torque & Chromeas, as well as provided content for private clients. Walsh has worked as a performance part-packer and classic car show promoter, now serving as crew chief for Nitrousfitz Racing.

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Photo Credits

  • T.A.C. 2009