I purchase a 1/4" tap and drill, plus recessed 1/4" plug 9the kind with the square dent in the top of the plug.
Drill out the bottom shell of the torque converter and let the fluid drain. It can take a couple of hours. 9-12 quarts total including what's in the pan.
Tap the hole, wrap the plug with teflon tape, then tighten but I don't play King Kong with strength of installation.
Job semi-finished. Torque converter and oil pan buttoned up.
I install SIX QUARTS of ATF into the oil pan, then start the engine. Range the selector drive-neutral-reverse. The pump will suck up all the oil in the pan. Start adding more fluid while carefully checking the full mark on the dipstick.
The burnt friction material, bronze bushing powder and steel filings (pump) hiding in the bottom (they gravitate down when draining) will depress you.
No worries about drilling into the converter. Any drill debris gets flushed out by the fluid.
And the quarter-inch pipe plug does not imbalance the torque converter enough to matter one whit.
I've enjoyed 300,000+ mile lifespans on THM 350 and THM 400 transmissions by using the full-drain maintenance. First drain at 50,000 miles, then every 100,000 miles following.
Ford & MoPar didn't get a severe case of The Stupids when they designed their systems - both have torque converter drain plugs.
Although messier than snot, this mechanical driveway service is w-a-y cheaper than pump forced flushing and there is no way in hell pump forced back flushing will touch debris hiding in the torque converter.
The older Ford C4 and C6 transmissions used to use bug screens for filters. Good for stopping cigarette butts and pop tops.
