[greasefingers]

Abstract
Flushing the transmission is very controversial. People have reported that it can stir up resin/residue/gunk that can settle into things (like the governor pressure transducer) since this tranny uses electronics to determine shift points. This may be the case if one brings their vehicle into a shop for a flush? Instead I used the engine/tranny to pump the fluid out while constantly replacing it. The other thing I worry about is that a shop would also have to flush their equipment out with the type of AFT that I want; to avoid cross-contamination. I have successfully performed a flush with no issues using the method below. Note: this is not a novel idea. I have heard about people doing this from time to time, I just never had the guts to try until recently.
Purpose:
The reason for my flush is: I have always used AFT+3 which is NOT synthetic fluid and I wanted ATF+4 in there which is synthetic. My first 42RE transmission was replaced by the dealer with a re-man one at 160,000 miles for a total of $ 2,100. I now have 200,000 miles on her and want it to last as long as possible.
Tools:
1- One nifty special funnel from PepBoys at $ 7 that comes with a piece of tubing that fits perfectly inside the tranny fill tube & a shut-off valve from a company called FloTool. The funnel is called Measu-funnel pn# 10704.
2- A ¾” open-end wrench for the tranny line.
3- Fourteen quarts of Valvoline ATF+4 at $ 4.19/qt. Or any +4 AFT (I bought 14 quarts, as I do not know what the total capacity the tranny and torque converter).
4- 3/8” inner diameter clear tubing
5- Waste bucket (I used a 5-gallon HomeDepot orange bucket)
Procedure:
The important part of a transmission flush is determining where to tap into. The fluid leaves the tranny and enters the bottom of the radiator (passenger side). So you could tap in here but I do not like that quick disconnect connector, so I tapped in at the top of the radiator (driver’s side). Caution: I have a picture of a plastic line connecting to the tranny line here. This is not where you connect it. If you work from there then you need to connect the hose to the radiator port. After I got working, my hands where to messy to take a photo of the correct way.

I did not plug the hanging tranny line as nothing came out. Attach a piece of 3/8 ID clear plastic line to the tranny nipple that sticks out of the radiator port. Something slightly larger would be better as it is hard to push this onto the radiator nipple) 13/16 ID would be perfect but it may be hard to find that size. Then stick this tubing in a waste bucket. The day before this, I filled an empty milk container up with water and dumped the water into the waste bucket. Then I marked the inside of the bucket with a Magic Marker. Continue filling with water until you have five marks indicating each gallon poured in. That way you can measure how much AFT came out. This is the amount of new AFT that you need to make sure gets put in. This is a check or material balance.

The transmission is a very complex device. It has several feet of tubing/plumbing in it. Each gear shift selector position (Park, Neutral, Drive, etc) has its own separate plumbing circuit. Therefore when flushing it seemed that it would be important to move the selector into each position for purging that fluid circuit. To my surprise, fluid only flows out of the tranny in Drive, 1st & second. No fluid exits the tranny in Park or Neutral.

From here it is an easy job. Place lots of newspaper pages about for any spillage. Have a helper start the engine. Since the funnel I selected has a shutoff valve built into it, it is charged with a quart of ATF before the process. Once the engine is running, shout to the helper to place the shifter into Drive. Fluid will come streaming out into the waste container and at this time open the shutoff valve to the funnel. Once the container is filled to the one gallon mark, yell to the helper to shut the engine off. Repeat this procedure now for 1st gear, and then 2nd gear. Use the remainder of the AFT for the Drive gear again. Once 14 quarts has passed, you have purged the system as good as I can think of.

Results:
There is no difference in performance/shift behavior. I just hope that using the correct AFT will extend the life of my second transmission, as it was formulated to do! Also, I wanted a complete change rather than several quick drain and refills. You can drain and refill three consecutive times and basically achieve the same results, as this would be replacing the solution/AFT by dilution. It is a shame that the tranny pan has no drain plug.
Notes:
1- this is perfect for changing between different between types of ATF fluids. I will not do this at each 30 k mile interval. At 30 k miles I will do the simply drain and refill method. But I think it would be good to fit this into a maintenance schedule somewhere.
2- It is not a substitute for dropping the pan and cleaning the magnet, removing the metal particles from the wearing bits, or replacing the filter.
3- being as tenacious as one can be, you will still make some type of mess. So be aware that a roll of paper towels and a non-cluttered work space is necessary. Kitty litter absorbs oils well … hint hint
4- SAFETY ISSUE: the helper must apply the brakes while you are performing this task. You have to watch the ATF level in the funnel going into the tranny, and the output into the waste bucket, in order to tell the helper to shut the engine off at different times. You should have the wheels blocked and engage the hand-brake. Therefore it is important that you trust the person behind the wheel. Helpers or assistants should not include any of the following people: x-girlfriend, x-wife, or anyone you owe money to. It would just be too easy for them to ……..

Once done, you are assured that you have performed a thorough job meaning that the correct fluid was replaced without any cross contamination…and that the job was actually performed in the first place! Can you tell that I don’t trust people?

Take your time and think through things once everything is hooked-up.

Things can go wrong, so please do this at your own risk. I am not a professional mechanic.

[greasefingers]

Please note that the second picture in my post is wrong. I tried to indicate this, in the photo, with a red X inside a red circle. However, I do not have fancy photo editing software and I used Microsoft Paint to accomplish this. The editing attempt did not turn out as well as I wanted. Hence the crappy color and hard to see “X”

[greasefingers]

You will end up with a lot of waste in the end. My family does so much laundry that we buy large 2.3 gallon containers of liquid Tide. These are perfect for waste disposal containers. You will need two of these as you can see from this photo that I have a lot of AFT to bring to my local municipality.

[SJZ]

Nice writeup! Thanks for taking the time to document the procedure.

[zaq123]

Great Job Steve
It's the only reason I stopped doing oil change myself, too much waste
Between my 2 GCs I change oil every 6-8 weeks. However I wouldn't let anyone changing my tranny fluid

[jagszj]

Thanks, this is a great method

[Finaltheorem47]

Yeah this is great. We burn our oil through our heater and ATF through our diesel truck haha.

I'm surprised you only got fluid coming out of D,1 and 2. I thought it was supposed to be flowing through the cooler in every range except for park.

[Carllo]

Thanks, great explanations, congratulations!!!