I am pretty sure that the rear has the stock posi trac lok unit from looking at pics, but not 100%. I am guessing it needs to be replaced, though I am not sure exactly how it engages.

With the rear supported on jack stands spinning one tire results in the other tire spinning the same direction. If I turn the pinion yoke by hand and hold one tire it will still turn the other free wheel, though it is slightly difficult to do, it doesn't seem like there's anywhere near the force needed there should be.

Looking into the carrier, on one side there are 2 clips ( 180* apart ) that appear to be broken and another part that fits into them but now rotates away and has dug into the carrier housing. It still rotates back and forth. The opposite side still looks intact and not broken.

So, does this sounds like the stock setup?
If so does it sound like it's no longer working properly?
Is this rebuildable?

Questions are mostly out of curiosity since I ordered a Detroit TrueTrac unit for it.
If it is serviceable, or worth anything ( it's the 3.92 and up carrier ) and anyone is interested I'd be willing to let it go for the price of shipping once my new differential gets here.

 

my dana 44 does the exact same thing. always has ever since i had it. works flawlessly.

 

Hmn... maybe a load is required, like actually driving the car to get it to engage properly?

I'm pretty sure those clips are broken and not working correctly and that other part shouldn't be rotating free and hitting the carrier housing. I'll have to get a picture of it. I've never had the rear in the car so not sure if it worked or not.