Torque Converter Drain Plug Install 700R4

[beanious]

Hello everyone, I’m rebuilding my 700R4 transmission and while I’m in there I thought I’d install drain plugs and flush the torque converter (TC). Conventional wisdom is to always replace them, but since I know the TC was working well prior to removal, including lockup, I thought I’d turn it into a fun project and flush it. What follows below is the inspection, modification, cleaning and painting of the torque converter. I hope this little project can be of use to the community, thank you.



Inspection:
Inspect the internal bearings by inserting the input shaft-drum and rotating, should be smooth
Inspect the bearings again by taking a screw driver or pick and move the TC stator threads back and forth; it shouldn’t move out of sight, I’d say 3/8” movement
Inspect the stator by inserting the stator shaft-pump and rotating, it should spin free clockwise but some resistance counter clockwise
Check TC shaft for ridges, if so consider replacing
Drain the TC by flipping it upside down into a pan

Modification:
First step is to determine where you want to put the plugs, I measured 1/2 of an inch from the line where the two parts of the case meet and marked
Second step is to measure the outside diameter of the TC, divide in half and mark.
Having two drain spots makes it easier to find a drain when servicing and helps make sure the balance of the TC isn’t thrown off
Verify the holes are marked in the right places
Center punch where the holes are going to be
Drill one side with a 1/16 bit and drain the TC in a pan by turning the TC up on its side, got another quart of fluid out of it

I used a neodymium magnet to clean up the shavings as I went along the drilling process below
After drained drill the hole out to 1/8, ¼, 21/64, I used a ridge reamer to clean up the holes
Be sure not to drill too deep as once you drill through, the impeller is on the back side

I tapped the hole using two 1/8 NPT taps, one was a normal tap and one I ground 5 threads off of so it would still tap but not hit the turbine
I repeated the same drill and tap process for the other hole
I sourced two NPT plugs from Ace hardware; I recommend the type with the six point external fastener as they can hold up to much more torque
One thing to keep in mind is how deep the plug threads sit in the TC, I measured the thickness of the TC at the tap site and ensured the plugs went in the same.
It is possible they can hit the internal parts of the TC
I made up some transmission parts cleaner by using 75% mineral spirits and 25% ATF, this solution is safe for clutches, paper or Kevlar friction materials and bearings but will cleanup gunk-residue
I flushed the converter with the cleaning fluid until it came out clear with no debris, probably six times or so. I used a coffee filter to clean the debris out of the fluid and reuse, but I did change cleaning fluid once.
Next was running a half quart of straight ATF through and drain, I did this twice to remove the remaining parts cleaner
I coated the 5 threads that go into the TC of the plugs with ARP thread sealer and torqued them to 10 ft/lbs.
Then I labeled the plugs to their holes using a engraver

I painted the converter with silver matte exhaust paint, I like to use matte paint on transmission parts as it shows leaks better than gloss or semi gloss.
Then filled the TC with 1 quart of ATF and covered the center opening with saran wrap and rubber bands to keep it clean
At this point it is ready for install, when the service interval hits I now can drain the transmission, install a new filter and also drain the TC ensuring a complete fluid change.


Below are some info for fluid conversions that I used.

1 cup = 8oz

2 cup = 1 pint

2 pint = 1 quart

1 quart = 32oz

4 quarts = 1 gallon