I searched and searched can't find out where to find my gear ratio. I found a thread which said it was on the passenger side next to the VIN number but couldn't find it. I do belive it should be stock 3.73

 

There's a two letter code that says what axle you have. From there I believe you look it up in the owners manual.
I also looked for the Superduty FAQ that used to be a sticky in the 6.0 forum that had an axle decoder, but for some reason it's been removed. Don't know why.

 

Some of the door pillar tags (like mine) do not have a code except for "XX" under the axle area. For those you have to crawl back underneath the rear and look for a tag on the differential. next to the bolt hole that holds the tag on is a code like 3L73 X the ratio is the numeric portion and the L indicates limited slip. it won't say anything if it isn't. the X is some other code. Some of the bigger diffs have the tag in the front on a bolt. read them the same way.

 

Old time trick that is foolproof (unless truck falls on you) jack it up by the pumpkin, put a chalk mark BDC of drive shaft, like wise on a tire. Rotate the tire one revolution and count the number of times the drive shaft rotates. This will give you an accurate ratio no matter what size tires you may have installed.








bdc

 

Mine said L73 10

 

OK you have 373 limited slip 10.5 ring gear .