What does the tag on my diff cover indicate? Also, there's a few other numbers on the rear axle that I'm not sure what they mean.

S 8 3 2 J

3 1 8 8 5 A 1 8

https://photos.app.goo.gl/h4hp4i3r5Ti8iTscA

 

https://www.fordification.com/tech/rearends_ford15.htm

3.31 open according to that.

 

I found it finally. It looks like S832J is a 3.31 ratio. I think the NL might mean Non-Locking? Also, I think I missed a digit in the pic. The first three digits on the bottom should read 331.

http://www.fordification.com/tech/rearends_ford15.htm

 

Thanks @BLDTruth . I didn't see your post while I was writing mine.

 

Yes, it's very common for the 1st digit on the 2nd line to be under the bolt head.


(phone app link)

 

You were asking about swapping to 4.10 gears in our PMs - here are the part numbers I would recommend for swapping in a brand new limited slip carrier with 4.10 gears:

M-4204-F318C
M-4209-88410

You can also go with a detroit locker style differential which is much better overall but costs twice as much. Just depends on how you use your truck.

If it is a 4x4 you will obviously need a matching ring and pinion up front - and unfortunately that means a new carrier as well because the dana 44 needs a carrier change when you go to the 4.10's. It is a much bigger PITA to do the front than it is to do the rear. The front requires disassembling of basically the entire front axle to remove the pumpkin, which means removal of the brakes, hubs, spindles, etc . If you choose to do it, I would highly recommend being prepared to rebuild the entire front end, depending on what you know about the maintenance history. I ended up purchasing a complete dana 44 center member off of ebay that already had the 4.10 gears installed. I use 4x4 maybe once a year so for me paying $600+ for new stuff up front just wasn't worth it.