I need to stop reading on the internet. Someone please save me more hours of reading. My 2008 Lariat 5.4 4x4 has a axle code of 19 on the door sticker, which what I've read means 8.8", 3.55 Open diff. However it's a 12 bolt trapezoidal rear cover which from what I've read is a 9.75". Needing to replace the pinion seal and I need to know which size I have. I'd be really surprised if the rear axle has ever been swapped in this truck. Axle tag is not readable. Completely rusted

 

That is a 9.75 axle. The trapezoid shape makes it easy to spot. I believe if you have a 5.4 engine you will have a 9.75 so that's another way to tell.


the 8.8" is more of a rectangle with rounded corners

 

So the 19 axle code on the door doesn't mean 8.8 at all? That's the only thing that threw me off. I found a chart on here somewhere that says it was an 8.8"...but all the pictures I've seen this didn't match.
Appreciate the help!

 

I found this article and the picture of yours looks a lot like the 9.75 diff:
https://www.differentials.com/techni...dentification/

 

19 means 3.55 open diff, that is all the code tells you. Looking at the cover is the best way to tell 8.8 vs 9.75.

There were even some trucks that had a 10.25" but they have 7 lug wheels...

 

Thank you very much! I appreciate the help! Time to head to the parts house and get it on the hoist!

 

Front diff is 8.8 on that truck.

 

Clearly the rear diff (op also asked specifically about the reardiff, not the front), but yes.