Locks when it shouldn't

[TrialByFire]

I know you're usually on top of your game with this stuff.... but when was the last time you replaced all the driveline fluids? And did you add the additive to the diffs?

^^^That was the first thing that jumped into my mind while reading this. Have you been adding the friction modifier to the diffs? It sounds like classic symptoms.

Well the T/C was replaced more recently but I have not replaced the diff fluids in about 30,000 miles and did not use the friction modifier, so that is a real possibility. When I disconnected the ELSD cables and still had the problem, I assumed it was the brakes doing it. I have always thought that QD-II uses the brakes in addition to the ELSD but nothing I have read recently supports that assumption. I know that the ESP definitely uses the brakes.

I'll change the diff fluids and let you guys know if it helped.

[Matt]

Im gonna say thats a real possibility now. I had a similar issue with my front diff.... had to change the fluid twice to completely resolve the issue I was having (binding popping sound in front).

Get enough fluid and mopar friction modifier for two complete changes. It'll probably get better a few days after the first change... then a week or so of driving change it again and you should be good. It takes some time for the fresh fluid & additives to work its way into the clutches; so dont be discouraged if theres not an immediate improvement.

[Matt]

Oh and QDII equipped vehicles still utilize BTC. But you would know if it was the brakes because you'd hear & feel the ABS pump kick on. Its obvious when it happens too (mine kicks on once in a while if I make a quick sharp turn)

[TrialByFire]

Oh and QDII equipped vehicles still utilize BTC. But you would know if it was the brakes because you'd hear & feel the ABS pump kick on. Its obvious when it happens too (mine kicks on once in a while if I make a quick sharp turn)

Thanks. I'll let you know.

[07JeepXK]

Any reason why you didn't add friction additive??

[TrialByFire]

Any reason why you didn't add friction additive??

I didn't do the work.

[07JeepXK]

Ahhh that makes sense. I was going to say.

[TrialByFire]

Well we changed the fluids Wednesday night and there seemed to be an improvement during straight-line driving, but during turns the violent thrutching was still present unless I threw it into Neutral and coasted through the turns. Friday night while driving home, I lost drive and started hearing some ominous noises in the rear end. I pulled over, popped it into 4-LO and drove home in Limp Mode (FWD only?). A look underneath today revealed that in 4-HI the rear drive shaft is turning but the rear wheels aren't (but they 'try' a little)! Thinking the worst, I suspect the rear diff/ELSD is gone, however I am searching for alternatives so I don't bark up the wrong tree and waste a lot of $$$ and effort tearing the rear end apart. My question is, is the 'default' (i.e. unpowered) ELSD mode unlocked where there is no torque to either rear wheel? I disconnected the FDCM to reset it, then plugged it in again (no difference in behavior with it unplugged). I am now getting a U0114 code (no comm with FDCM) but I expect that to clear after a few (more) starts.

[Matt]

The unlocked (or "off") mode of the ELSD is equivalent to an open rear.

I'd take that diff cover off and go from there. Given your symptoms and how it just ended, it sounds like your gears are shot. Don't drive it. If you've stripped some teeth on the pinion then A LOT is salvageable (though i'd probably replace the carrier too regardless... never know where some metal shavings ended up).