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

[Sheepdip]

Not trying to rain on your parade but I'll bet those pipe plugs leak. Not enough thread engagement to seal. Teflon tape and pipe dope are not sealers per say they are lubricants, the stretching of the tapered threads are actually what seals and holds, that's why they make what's known as a "Boss" to weld onto thinner applications such as what you have.

A typical 400 converter operating pressure is around 200 P.S.I. that brass plug with all the threads that should be engaged, roughly 75%, when properly tightened is rated for 150 P.S.I.

[Shinysideup]

/\ What He said, and you have created an inbalance that will whipe out bearings. More inportantly there is NO WAY you got all the shavings out.

You could do a complete flush on the trans cooler line hookup without all the problems youve created.

Top notch skills on the write-up process, however I wouldnt do this mod or recommend it.

[72LB]

I would think the balance will be off regardless of using the two plugs.

[hugger6933]

your gonna be fine. I had a 07 K1500 that blew a cooler in the trans and to try to get the coolant out of the converter I drilled a 1/8 inch hole to drain said converter. Now let the flames start building but once drained I put a screw from a late truck with a 7mm head I just screwed it right in no big plans like this poster did. Now that truck has gone like 50K miles since then no leaks no trans problems. There are fragile systems on these trucks but that drain plug isnt hurting anything. The factory probably stopped using them cause they added something like .002 cents to a build

[beanious]

I greatly appreciate the feedback guys! All over the internet you hear you have to buy Torque Converters new, but it's from manufacturers or people who bought new TCs. There are ASE master techs out there and transmission re-builders that I know personally that do this and have had them last 150,000 miles so there is some truth in being able to install plugs and drain them.

With the balance issue, I'm sure there is no way it would be good to 10,000 or even 7,000 rpm, but it's 70's small block Chevy with a redline of 4,500. I mean they welded two identical standard sheet metal plates to the sides with no balance tack welds, or balance drill holes like in a crankshaft. Looking at the welds they used there is scatter around the seam, looking at the factory balance and duty RPM of 2,000 there will be no issues there.

With the pressure capabilities, I have a pretty good amount of thread engagement. You would think like two or three threads, but this is one of the thickest areas of the TC. I was able to tap 7 threads in, so much that I ditched the automotive recessed allen hex plugs because they had less thread engagement than the taped hole they were going into. Also the plug and ARP liquid thread sealer is the same I've been using for the last two transmission rebuilds. When I plug the line pressure ports and external lockup sensors I use it and no problems so far, stuff is amazing.

With the metal debris, if no precautions had been taken, for sure there would have been shavings in the torque converter. However I used strong neodymium magnets while and after drilling to cleanup the shavings; after I used neodymium magnets throughout the flush process to ensure they were getting caught and removed, I swear I must have flushed it like 10 times just to be sure.

I love posting here because it creates the ability to discuss topics that are controversial and have no rock solid answer out there. There are people who have and currently do this to torque converters. I see this topic similar to when you have a 700r4 with ANY problem and 10 people chime in with "have you adjusted the TV cable", which is important, but not always the solution. Proof is in the pudding, so I'll report back in as I put mileage on the trans-torque converter and let ya'll know it works out. Happy holidays!

[chewychevy67]

I have a 67 variable pitch turbo 400 and when I bought my remanufactured converter it had a drain in it. My transmission guy wasn't the slightest concerned about it so I'm sure it will be fine. He said he has seen many over the years with them.

[AussieinNC]

Before you put the trans back in, install the convertor in the trans and spin it to check the new plugs do not contact the inside of the trans housing...

The convertor balance weights on the convertor are minimal height above the convertor housing for clearance reasons....

The plugs should not have any issues with leaks etc, but as mentioned in other responses, you can pop the cooler line out and flush the convertor fully as a service process....

Convertors should always be fully dismantled when a trans is overhauled as "flush cleaning" processes never remove all deposits, nor will the flush process permit a thorough inspection of the internal components....

[beanious]

I wanted to post an update to the forum for the results of adding the drain plugs to the 700R4 torque converter. I just did my 15,000 Mile transmission fluid change which included draining the torque converter using the 1/8 NPT plugs I installed. No leaks before or after. The drain ports made the fluid change easy-peasy. Guess it worked out pretty well after all, I'll check back in after another 15K.

[WorkinLonghorn]

Originally Posted by beanious

I wanted to post an update to the forum for the results of adding the drain plugs to the 700R4 torque converter. I just did my 15,000 Mile transmission fluid change which included draining the torque converter using the 1/8 NPT plugs I installed. No leaks before or after. The drain ports made the fluid change easy-peasy. Guess it worked out pretty well after all, I'll check back in after another 15K.

I managed a big-name transmission shop in '79-'80 and we did this a quite a few times. Never a problem but we did have plugs that were designed for this purpose, for one thing they were much smaller and lighter.

[ChevyRacefan]

Cool, Project. I wonder if using a nutcert and then a short bolt and copper washer.
How thick was the metal of the converter that you installed the plug in?
I am surprised the balance issue hasn't taken out the transmission pump/bearings.

[beanious]

Hello, balance isn't an issue as there are copper plugs evenly spaced 180 deg. around the torque converter. I drilled and tapped the overlapping material on the converter, so plenty of metal for the threads. Read above for the deets, not really surprised it worked this has been around since the 1960s. See the posts above, still running great!