04 KJ Trac-Lok rear diff problem

[Burevestnik503]

I recently inspected my 2004 Renegade and confirmed it has rear diff Trac-Lok. For some reason, Trac-Lok doesn't seem to work when I'm off-roading, whether I'm in Full Time, Part Time, or 4L. When one rear wheel and one front wheel are loss grip in same time, the vehicle loses virtually all forward motion.
I left the rear wheels in the air and manually rotated the left rear wheel with the parking brake released and the gear in Neutral with the transfer case in 2WD. The right rear wheel turned in the opposite direction, and I didn't see any sign of syncing or synchronization between the two wheels.
Notably, my rear differential fluid is clear, indicating the Trac-Lok system isn't damaged. Are there other possible causes for this problem? Also, if it's important to know, my cruise control stopped working a while ago, and I haven't been able to pinpoint the cause. I'm not sure if the two events are related.
Besides this incident, I recently experienced the transmission getting stuck in 2nd gear twice. On one occasion, the OBD indicated an overheated transmission, but I had just started the vehicle and was exiting a highway service area. Another time, there was no fault display, and everything returned to normal after I turned off the engine for a while and restarted the vehicle.

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[KJowner]

Probably needs a fresh set of clutches in the diff, they wear out, especially if the wrong oil has been used.

 

[Burevestnik503]

Probably needs a fresh set of clutches in the diff, they wear out, especially if the wrong oil has been used.

I purchased a new Trac-Lok rear diff, but I'm not sure if I should attempt to replace it. Since my car is used, I can't be sure if the previous owner had the correct LSD fluid before it came to me.

 

[KJowner]

Not too hard to replace but you need a special tool to set the diff up afterwards. Lots of information on here if you search.

 

[u2slow]

Somebody may have overdone it with the friction modifier additive.

Try flushing all the oil out (brake-kleen, etc) and reload with basic gear oil. See if you get any grip back.

Fwiw, I haven't put modifier in our KJ in 13 years. Several gear-oil changes later. Grips just as well as when we got it.

 

[WWDiesel]

Clutches in the TL are probably worn out, time for a rebuild, replacement, or upgrading to a true locking rear differential.
913A368 Detroit Truetrac Chrysler 9.25" Rear Dodge Ram Limited Slip Differential

913A368 Detroit Truetrac Chrysler 9.25" Rear Dodge Ram Limited Slip Differential

913A368 Detroit Truetrac Chrysler 9.25" Rear Dodge Ram Limited Slip Differential<br />APPLICATION: Chrysler 9.25" Dodge Ram Lsd<br />AXLE PLACEMENT: REAR<br />AXLE SPLINE COUNT:31<br />SPLINE DIAMETER:1.32"<br />COVER: 12 BOLT <br />GEAR RATIO: 2.76 THRU 4.56<br />MODEL:CHRYSLER 9.25" <br />RING...

www.drivetrainamerica.com

 

[Burevestnik503]

Clutches in the TL are probably worn out, time for a rebuild, replacement, or upgrading to a true locking rear differential.
913A368 Detroit Truetrac Chrysler 9.25" Rear Dodge Ram Limited Slip Differential

913A368 Detroit Truetrac Chrysler 9.25" Rear Dodge Ram Limited Slip Differential

913A368 Detroit Truetrac Chrysler 9.25" Rear Dodge Ram Limited Slip Differential<br />APPLICATION: Chrysler 9.25" Dodge Ram Lsd<br />AXLE PLACEMENT: REAR<br />AXLE SPLINE COUNT:31<br />SPLINE DIAMETER:1.32"<br />COVER: 12 BOLT <br />GEAR RATIO: 2.76 THRU 4.56<br />MODEL:CHRYSLER 9.25" <br />RING...

www.drivetrainamerica.com

Worn out has been confirmed.
I've decided to replace the new Trac-Lok rear diff.
The only problem is, I can't seem to find the modifier in my local Mopar shopping list. A friend suggested using the GM modifier, but I'm not sure if that's appropriate. My local Jeep dealer suggested using 75W-140 gear oil without the additional modifier. Is that possible?

 

[KJowner]

Not a good idea to run without it, it helps the plates slip without wearing. Any LSD oil should be OK.

 

[u2slow]

Not a good idea to run without it, it helps the plates slip without wearing.

I disagree. I see it as break-in juice for a new unit.

If a diff needs it's, it's tells you by its behaviour on a test drive.

 

[LibertyTC]

Any Trac-loc rear diffs (clutch based locker) does require the Mopar 4 oz bottle of limited slip. Part# MS 10111

 

[Burevestnik503]

Any Trac-loc rear diffs (clutch based locker) does require the Mopar 4 oz bottle of limited slip. Part# MS 10111

Thanks. I'm in the process of having the dealership order it to me.
Regardless, I believe it's safer to use Mopar-certified products. I maintain both of my Jeeps with Mopar motor and gear oil.

 

[KJowner]

I disagree. I see it as break-in juice for a new unit.

If a diff needs it's, it's tells you by its behaviour on a test drive.

But it's not break-in juice is it, it's the manufacturers specified friction modifier fluid for LSD's. All limited slip units are supposed to use something to help the plates slip in normal operation to reduce wear, leaving it out is only going to do one thing....

 

[u2slow]

But it's not break-in juice is it, it's the manufacturers specified friction modifier fluid for LSD's. All limited slip units are supposed to use something to help the plates slip in normal operation to reduce wear, leaving it out is only going to do one thing....

It's to alleviate tightness, noise, and excessive tire scrubbing... which is common on new units.

I've left the modifier out of my limited-slip axles for 20+ years (all used units) no problems; just good traction. Except - when the unit itself is inadequate for the tires, power, and payload it's subjected to.

 

[Burevestnik503]

Not too hard to replace but you need a special tool to set the diff up afterwards. Lots of information on here if you search.

The good news is that I already have everything I need. I plan to complete the replacement during my downtime in the next few days.
However, I can't seem to find any forum posts on how to set up the diff after installation—mostly references to the modifier MS 10111. So, what should I do?

 

[u2slow]

You need the big hex tool to slide down the axle tube to adjust the carrier bearings for backlash and pre-load. I made mine with a big nut welded to each end of a length of 1/2" rigid pipe.

 

[KJowner]

There's a lot of info on setting it up in the manual + YouTube videos, much easier than trying to explain it on here

 

[Burevestnik503]

Status Update
I've installed the new Trac-Lok LSD. It's working fine now.
The repair shop provided me with the special tools. However, to my surprise, it seems to require a bit more rear differential fluid than I expected (the dealer told me it requires about half-liter more than a Wrangler with the same DANA35 rear axle).
All is working fine now. Thanks for your help.

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