Locks when it shouldn't

[TrialByFire]

Is there a good writeup somewhere that describes exactly (not generally) how the QD-II works? The reason I ask is that I have been having intermittent problems where the drive system seems to leave the system fully locked (I know, being hydraulic, the ELSD never really 'locks' ) and snaps and lurches in corners at low speed in both 4-Hi and 4-Lo. It has been getting progressively worse the last few weeks but I took a trip to Colorado anyway this last week to pick up my son from a summer school class in Pitkin, taking in one hard 4x4 trail for grins. I had no problems on the trail but on pavement it's now making a racket in turns and even 'popping' a bit at highway speed going straight. It seemed like the ABS system was randomly braking one or more wheels, so I pulled the ABS fuses but still had the issue. Next, I tried unplugging the front and rear ELSD cables from the diffs. Still no change. Reading the shop manual, there appear to be a couple of other possible sources of the problem: the G-sensor (used in the anti-roll logic), and the steering position sensor. The manual doesn't cover how those inputs are used but I suspect the steering position is used to predict differential wheel speeds and allow slip while turning. If the G-sensor was bad, it might think the vehicle was starting to roll and brake the outer wheels.

It isn't throwing any codes that I can see, and the behavior was present before I upgraded the front struts/springs so I don't think that was a factor. BTW, it does'nt do it while in Neutral coasting. Any ideas (Matt)?

[Matt]

Next, I tried unplugging the front and rear ELSD cables from the diffs. Still no change.

This is the troubling part.... if you've unplugged the solenoids the diffs should be open and remedy your issues. Makes me wonder if its more of a t-case issue. Even with open diffs, if your t-case clutches are engaging you'll get driveline binding. Either way it sounds like more of a mechanical issue than a bad sensor since you're not throwing codes.

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?

[Matt]

And just as a side... you're not at fault for saying they "lock". When functioning properly these diffs do provide full axle "lock" (ie not allowing differential wheel speeds).

From: http://www.eaton.com/EatonCom/Produc...disc/index.htm

EGerodisc™ is a hydraulically-operated electronically controlled limited slip differential that provides variable torque up to full axle lock. It automatically identifies the optimal traction solution at any speed. The EGerodisc™ is a commercially proven technology in production on the Jeep Grand Cherokee. It provides superior vehicle cross-country mobility and improved control for safety and roll-over protection. The electronically controlled actuation provides rapid response for stability and traction control. It eliminates driver interface; no driver training is needed. The EGerodisc uses standard gear oil and is virtually maintenance free.

Good video showing how it works:

[lekmedm]

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.

[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.