88XJ AW-4 trans: Wont move when cold, works fine when warm

This problem has slowly grown worse over the last 6 months on my 88 XJ. When the truck has been sitting for over 3 hours, shifting into any gear seems to do nothing but sit and spin in the driveway. If you rev the engine up to 3000 rpms, within about 10-15 seconds the trans will lurch and then bang into gear. Reverse is worse than forward gears as it takes longer to engage. Once it bangs into gear, there is no problem shifting from nuetral to that gear again. However, if you get it to bang in Drive, you will still have to do the same for Reverse and vice versa. Lately, on cold mornings, drive doesnt seem to bang in all the way, and still feels like it slips a little. Sometimes, it revs out first and doesnt want to shift to second unless I burp the throttle off. Then everythihng works flawlessly for the rest of that trip no matter how far or long I drive.

It seems a lot like a bad pump (or pressure regulator?) to me, due to my past auto trans experience, or a clogged filter or low fluid level. I pulled the pan, fluid looked good, filter was very clean, but I replaced them both anyway. I checked that I had the correct fluid level and ATF type (so please lets not make another ATF thread). Problem remains exactly the same. I can't imagine I'm the only one to have this problem. I'm going to disconnect the TCU tomorrow morning and see if that has any affect. I have the service manual, but the troubleshooting steps are quite extensive and I dont get much time between tests before the trans heats up and the problem goes away until I leave it for a while. any thoughts?

Sounds like it could be a lack of line pressure when cold which builds over time. Could be tested with the proper equipment.

How many miles on this transmission? Could be getting tired....

Your symptoms are classic for leaky seals in the pump. You might try a can of TransMedic or even a cup of lacquer thiner.

Lack of pressure is what I suspect, leaky seals in the pump was what I was targeting in on. I guess I need to get a pressure tester and give that a run. I did run trans medic through it with no change. What I don't want to do is drop the trans, replace the pump, and be right back where I started.

Sometimes Murphys Law and I have these bouts of misdiagnosis, "Hahah, its something obscure this time!"

You sound fairly knowledgeable, why not grab a salvage yard box and throw it in--sounds like this is your DD--and then rebuild yours?

I considered that, would run me about $200 bucks. My concern is picking up some other problem like worn plates or bad solenoids. I figure if this is just a pump, I'd rather swap in a new pump for $100 and then have the peace of mind that everything else is reliable, maybe replace the friction plates for good measure. My old beast has 250,000 hard miles on it with no rebuilds and is my safety net more than anything else. I live in SoCal, ride my sportbike most every day to work, and use the jeep for commuting on rainy days, family rides when my 04 Grand Cherokee is with the wife, towing the dirtbikes out to the desert and some other 4x4 antics since its so insanely capable. I've grown rather attached to this old Heep. The renix has proved itself time and time again in the worste situations out in the rocks and dirt.. and the 2WD/AWD/PTime/LOW transfer case is outstanding as well. I'm not letting it die until its at 1/2 million miles!

Well, if you can get by without it then just pull the box and rebuild it. Heck, you must have one free weekend a month?

Weekend... ugh. Space is so limited! My 68 Camaro has been jockying for priority in the garage for its engine swap for 2 years now, but my Honda VFR is already there on stands mid teardown amongst all my other toys. I know I know, cry me a river. If I can't do it in less than 48 hours, it doesnt get done anymore!!! I need a barn!!!