Transmission overheating, why?

I need help with this one...Yesterday my auto transmission overheated on a normal trip to work after about 15 miles of driving. It was 95 degrees out but this is the same trip and temps I've driven hundreds of times before without an issue. It is easy, in town, 45 mph with a few lights here and there. I noticed a hot oil smell right before stopping at a light and then it would barely move from the stop. I had to throttle it hard to get it into a parking lot on the corner. The trans. spit a little fluid and was very hot. The engine temp. was normal. The front diff. was just warm. The rear seamed normally hot but I would not get burned touching it. I picked it up on my trailer and took it home. Of course after cooling, it runs perfect. I jacked up each end with the transfer case in neutral and all four tires spun freely. All fluids are good. The cooling system is basically all new. The trans. fluid and filter are recent and clear with no water intrusion. Both fans are working correctly. I would call this XJ over maintained and not abused. All we have in FL is water, sand and mud. It has 135K miles and a 3.5" lift and 31" tires for a couple of years.

Here's were the diagnoses gets complicated! Last weekend I installed (nameless) lunchbox lockers in both axles. The installation went smooth and all specs. and backlash measured perfectly. They seem to work properly. While on the lift I also changed all the brakes (everything) and all seems good with those. Due to the lift already in place, I took the opportunity to correct the drive line angles at this time also. This included a 1" TC drop, leaf shims and tweaking my adjustable control arms. All this made the ride super smooth. Theoretically, this should lessen the strain on the drive line. Again, I can spin all wheels freely and easily hand turn them by the drive shafts.

To add more headache to figuring this out, I put it through a very wet ride with my local Jeep club a couple of weeks ago. Due to recent rains, we're talking 2.5 ft+ of water crossings. It did great and didn't even sputter the whole night. No blown fuses or other lingering water problems that I know of. I thought of the trans control but it seems to be shifting properly.

Sorry for being long winded but I thought too much info is better. It can't be coincidental with all this new work and the recent deep water. Where do I start? I don't want to overheat it and cook the tranny. I'm sure the problem is right in front of my eyes. Any ideas?

You might have ingested water into the trans through the vent tube from your deep water driving. Drain the trans and refill with fresh fluid and see how it drives.

There doesn't appear to be any water in the trans fluid but I will do a flush just in case. Thanks

You didn't specifically say you checked your fluid levels. Did you and were they in range? Like the man said, it never hurts to change the fluid.

You might have a seal in the pump going bad, not providing enough pressure to make the torque convertor to work correctly. The torque converter should lock up on the highway, but even without locking, it shouldn't run hot.

The next time it happens, see if it engages correctly in reverse. In reverse, the pump is configured to bump up the pressure.

PM me and I can point you towards the factory AW4 rebuild and diagnosis manual.

Honestly, (and this sounds crazy) to me it sounds like a brake issue. You said you recently replaced the brakes. A couple years back I replaced my front brakes with all new stuff. Drove for a couple days no issue. One day on my way to pick the kids up from school I noticed that the Jeep was getting awefully hard to move. It was taking more and more throttle to get it to move. Until it got to the point that it wouldn't budge at full throttle.

Turns out I had a brake caliper that stuck and wouldn't fully release. Once it got super hot it would release less and less until it was full on braking.

I'd take another look at the braking system. Check the rotors up front and see if it looks like they got hot.

I'd put $2 on it.

Sounds like the transmission got hot due to trying to push through the braking.

I had a similar issue with my 2000 that had 32s and a 4" lift on stock gears. If the ambient temps were above ~90 it would get so hot that the fluid would puke out from either the torque converter or pump seal. Once it cooled off enough, it didn't leak or have any other problems. An external tranny cooler helped my situation

Lowrange2 said:

Honestly, (and this sounds crazy) to me it sounds like a brake issue. You said you recently replaced the brakes. A couple years back I replaced my front brakes with all new stuff. Drove for a couple days no issue. One day on my way to pick the kids up from school I noticed that the Jeep was getting awefully hard to move. It was taking more and more throttle to get it to move. Until it got to the point that it wouldn't budge at full throttle.

Turns out I had a brake caliper that stuck and wouldn't fully release. Once it got super hot it would release less and less until it was full on braking.

I'd take another look at the braking system. Check the rotors up front and see if it looks like they got hot.

I'd put $2 on it.

Sounds like the transmission got hot due to trying to push through the braking.

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It's funny that you say that because two days before my passenger side caliper locked up. I didn't get far enough for the trans to overheat then. That's what prompted the brake overhaul.

Last night I found my rookie mistake. I trusted the looks of the fluid on the dipstick. Never trust what's on your dipstick or where it's been! After a complete pan drop and system flush I learned that FL swamp water and alligator poop is not an approved substitute for transmission fluid. Hopefully this or a second flush will do it and I don't have a rebuild in the near future...

Alligator poop may or may not be a fine substitute depending on the quantity of taco bell it had before the poop

How did the water get in the trans? Is there a vent at trans level?