This is from the factory service manual, regarding how to check the JK limited slip:

DIFFERENTIAL-TRAC-LOK®
A common problem of the Trac-Lok® differential is a chatter noise when turning corners. Before removing the unit for repair, drain, flush and refill the axle with the specified lubricant. Add a container of Mopar Limited Slip Additive after repair service or during a lubricant change.
After changing the lubricant, drive the vehicle and make 10 to 12 slow, figure-eight turns. This maneuver will pump lubricant through the clutches. This will correct the condition in most instances. If the chatter persists, clutch damage could have occurred.
The differential can be tested without removing the differential case by measuring rotating torque. Make sure brakes are not dragging during this measurement.

1. Place blocks in front and rear of both front wheels.
2. Raise one rear wheel until it is completely off the ground.
3. Engine off, transmission in neutral, and parking brake off.
4. Use torque wrench to rotate wheel and read rotating torque.
5. If rotating torque is less than 30 ft. lbs. or more than 200 ft. lbs. on either wheel the unit must be replaced.

 

Thank you!

 

if you look up the TRAC-LOK online many people call them TRASH-LOK. I got one with my JK b/c the dealership I bought my jeep from ordered all their JKs that way. I never expected much from it b/c of all the bad reviews I have heard. BUT I have been pretty impressed with it. I have followed Rubicons through trails they got hung up with open diff and had to engage their lockers to get past then I go through no problem with just rear LSD.

I think if mine was shot I would rather replace it with an eaton LSD (truetrac) instead of another "trash-lock".

 

Only 20k miles? How old is your Jeep? Should this be covered by your warranty?

 

I bought it used with 9000 miles on it, so no warranty.

I checked other shops in town. It may be cheaper to have this done in other areas, but here in Bend, it's $1200. If I supply the diff, its $800 in labor. Welcome to Bend!
I'm going to have the fluid changed and have them pull the cover so I can inspect it myself.
Then, down the road, have an Eaton installed.

 

Ouch. Think I'd email a few places in Portland or somewhere and check their prices, and maybe look into getting it swapped next time you're up in that area. Or wait until you decide to do gears?

If you want to save a little money, read through a few write-ups and pop the cover yourself. Changing the diff oil is super quick and easy. (and you may be able to tell something just from what comes out and what ends up on the magnet on the bottom plug). Popping the covers is a bit more involved, but shouldn't be a problem. Then just take a few pics of the insides and post them up to see if anyone here sees anything. But more than likely it will just be worn clutches that should show up with the test ronjenx posted above.

These are specifically for installing new diff covers, but same steps you would do.
https://www.jk-forum.com/forums/jk-w...w-pics-115712/
https://www.jk-forum.com/forums/jk-w...install-12618/

 

I used to do all fluid changed myself on my F150, but I live in a co-housing community where you cannot work on your car, plus I'm renting. I'm getting the fluid changed on the 16th and the mechanic said I can be there to inspect the rear end myself. I'll take pics...thanks, plus I want to do that test.
I never go to Portland, and I've never been. It's still 3-4 hours from here. In my younger years, I would have done this repair myself. I had a Miata and I rebuilt the top end of that motor...but age and circumstances change.....sucks.
I'll see what shows up at the fluid change......