I was hoping to do some maintenance on my new-to-me 1500 today. I'm all set to flush the trans and change the trans case, but I just went outside to ID my differentials and I have no clue. There's no tags on the bolts or any identifiers on the cases. The only thing I can still make out on the front diff is a 3.92 final drive. I would assume the rear would be the same, but that still doesn't help me.

Is there an easy way to ID the differentials after taking off the backing plates to know if I need 75w-90, 75w-140 or additives?

The truck has 138k and I don't have any service history, so I wanted to start from scratch.

 

I found some information from another thread.

Because I have a 1500, I will have an 8" front.
The build card was still in the glovebox showing a 9.25" rear with the LSD.

I love this site. Thanks guys!!