Transmission Gremlin(s)

[arosen1997]

So, since getting back to my JT in June, the transmission has been exhibiting some weird behavior.

Symptoms:

• When shifting from 1-2, the first shift of the day is wonky, seems to slam into gear.
• When shifting from 3-4, the first shift of the day is wonky, again, seems to slam into gear.
• When shifting into reverse if it has not been driven enough to perform shifts through 4th gear, there is a noticeable delay of 0.5-1 second longer than there should be before the reverse gear engages.

Things of note:

• If let to sit and idle for 5-10 minutes before driving, exhibits none of this behavior.
• These are do not appear temperature dependent, seems to be time dependent from the last time it was running, behavior becomes apparent if sitting for more than 4ish hours. I theorize this because It only does it after sitting for an extended period. For example, when I would drive to work in July and let my JT sit in the 110 degree sun or 6 hours, the transmission would still be ~120-130 degrees at the end of the day when it was time to go home and it would exhibit this behavior. However if I drove right down the street to the grocery store in the early morning, went inside for 30 minutes and came back out, the transmission will only be at 80-90 degrees when its time for the return journey and it will NOT exhibit the odd behavior.
• The strange behavior for 1-2 and 3-4 can be mitigated by manually shifting from 1-4 in the morning. Additionally entirely mitigated it RPMs are above 2.5k when performing shift and foot is taken off the gas.
• I'm at just over 70k miles, right in the window where the OEM ZF recommends a fluid change.

My Thoughts:
I really want to say this is a fluid/valve body issue. It really does not seem to be temperature dependent at all which makes me think it's not an issue with the clutch packs based off my experience. I will caveat that with my experience is almost entirely on the Allison MT653 in the equipment I work on. My working theory is my fluid is bad enough it's the root cause. It almost seems like there could be something fouling up the sections of the valve body when left to settle, but once the fluid gets moving around within the transmission it gets moved away and it's no longer an issue. I've seen that before on the Allison. I also worry that maybe there's damage to the valves that control 1-2, 3-4 and neutral to reverse because of the age and condition of the fluid. One other thing I have seen before is the gaskets between the valve body and transmission, or within the valve body itself developing a small leak causing similar issues.

Where I'm at now:
I've got 12 quarts of ATF (found it on sale in 6 packs so oh well) ready to do a fluid change and a filter on order (if Benny can get it in the mail). I'm debating whether it'd be worth it to pull the valve body and clean it. Or even just pick up an entire valve body and control unit since they're only 600$.

I'm really interested in everyone's thoughts. Particularly @ShadowsPapa, I feel like this would be a great topic to get your input on.

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[PuddleJumper]

I regularly check my fluid. I learned to do so on my old Toyotas. They never had a mechanical failure but they did like to burn fluid and would slip and shudder badly. A fluid change every 50 to 60k kept it feeling new. My last check i did on mine the fluid is finally starting to look used or "show" its wear. I'll probably change fluid next oil change. odo then would be 36,000~

 

[MrJeep]

I think you are spot on to change the fluid and filter first and see if that helps. I believe it will from experience with many other vehicles in this type of situation.

 

[arosen1997]

Okay, got the filter two weeks ago before leaving for hunting. Just got around to swapping the fluid and filter today.
Whoever designed the exhaust running where It does, I sincerely hope you stub your toe at least once a week. Made getting the pan off annoying.
The fluid I drained out was burnt, well beyond what I would have allowed had I not been away with my wife driving the jeep for 10 months since her car was stolen.
New fluid/filter is in it and I swear even just the drive from the shop to the house seemed smoother. I'm headed away this weekend and we're taking he wife's new car but I'll report back on Monday morning after driving to work how the new fluid and filter feel on that drive. I'll also go ahead and cut open the old filter on Monday and see if there's any goodies in there.

I will say, even though the fluid that drained out looked and smelled burnt, it tested within tolerance on our oil tester at work.

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