Hey guys. Ive got a 97 zj 5.2 awd (4 hi-4lo) ive read a little about flushing the trans by running a hose from the outlet into a bucket and in from a different hose. My problem is i dont know which is which. I have to replace my trans cooler as well and filter too. So i want to.do it all in one shot. What's the best way to.find out whats the inket and whats the outlet? Is it as easy as taking off both rubber portions and turning the truck on? Also i was planning on gettin one of the couple gallon buckets to make it as easy as possible. What should i get? Im new to jeeps but ive replaced trans filters before on some older fords. Never done a full flush on my own though so any advice is welcome/needed. If ajyone knows of a write up with pictures thatd be greatly welcome as well. Thanks in advance for the help!

 

If you wanted to follow the cooler lines from the trans the front cooler line is the out/hot, the rear line is the in/cold.

 

Awesome! Thank you. The trans cooler im going to is about 2xs the size of the stock one. Is that going to give me any issues in the cold weather? I wanna go bigger because im road tripping to the mountains this summer and with 3 people plus gear i dont wanna stress the trans too much in the heat. I will not be taking it offroad or anything though

 

Yes, if you don't run the radiator cooler as well, it won't warm up in the winter. I've worked on several classic hot rods that didn't have cooler coils in the radiator. They were fine until it got cold outside. My brother had a Chevy truck whose rad cooler popped, so he just ran an aux cooler. Worked fine until winter. The transmission just wouldn't shift right until it warmed up, which took a lot longer than the motor. The major source of heat in a trans is the torque converter.

The best way to flush a transmission is a transfer piston device, such as a T-Tech machine. It uses outlet fluid to push a piston and transfer new fluid into the trans. The return line to the trans does not "suck" the fluid back into the trans.

The last I knew, only Valvoline Instant Oil Change and Ford dealers used the T-Tech. That was 10 years ago.

 

Im not looking to bypass a cooler or anything. Just go to a bigger one. Will that give me the same problems dave? If so ill just get one the same size as stock. And im gonna have to google that tool to see if its something i can pick up. If not i may just have to have someone give me a hand to pour while im monitoring the fluid lol

 

You should be all right using a larger aux cooler as long as you still use the radiator cooler. I've seen guys use 2 regular jeep aux coolers in "series", that is the output of one into the other. You could even use an A/C condenser because it's okay with the fluid and pressure. The fluid going into the cooler is coming out of the converter and the return is going back to the pan. It's basically vented at between 20 to 40 psi, depending on the manufacturer of the transmission. I've even seen serious off-road rigs with oil filters in the cooling lines.

Just run the "hot" fluid into the aux cooler first. That way in the winter, you won't be warming the fluid up just to cool it down again before it goes back to the transmission. It should also remove some of the heat load on the radiator in the summer. (hey! this is basic thermodynamics, isnt it?) (Wow, I didn't think I was that smart!)

The T-Tech machine costs about $600 or more. There really isn't any other way to direct transfer the fluid.

 

Will flushing the trans this way flush out the torque converter as well? I know it may be a dumb question, but i know next to nothing about transmissions

 

Yes, the torque converter will be "flushed", but I hope you have a lot of fluid on hand. It will take close to 14qts of fluid to properly flush the transmission.

 

I was going to pick up some.in the gallon jugs. I just need to make sure i get the right stuff. From what ive read the transmissions on the awd jeep can be pretty picky

 

ATF-4 is what you want.

 

Thats what i thought. Thanks for the info! I figure this will be a long project ( a day) but hopefully shorter.

 

This is great information. If you didn't have a piston to push new fluid in to the transmission, could you add transmission fluid through the dipstick, start the jeep, and push out a say 2 quarts into a bucket, turn the car off and add fluid through the dipstick again? Keep repeeting this process of and draining and adding until you go through 14 or so quarts? Should we drop the transmission pan first, drain the fluid that's in the pan & replace the pan gasket, so when we start the process it at least is clean fluid threw the system? thanks

 

I just had the shop do this to my 97 ZJ. I asked my buddy how he did it and he took a big bucket then took the return line off of the Jeep with a hose going into the pail, put the Jeep in neutral , and dumped new ATF down the filler neck while the old fluid flowed out using the transmission pump.

It made a huge differance, my tranny shifts like it's brand new now. It would probably be easier to do this with a buddy to turn the Jepp off and on for you.

There are videos out on YouTube that will show you how to do it.

Tony