Jeff Campbell

Is there a way to tell what gearing I have from looking at the rear differential? I know there are specs in the door jam but I have a suspicion that the rear end may have been swapped at some point before I bought it. I dont want to tear anything down just on a hunch so if I cant tell from looking at it I will assume it is stock, lol. Thanks guys and keep up the good work.

sylver91

Should be a tag on the diff. Little tab of metal usually bolted on the rear cover

Never_Evil

If that tag is not on one of the bolts holding the diff cover on, it might be time to change the fluid anyway. Take the cover off, catch the smelly fluid, and the pinion face should have the ratio stamped on it. Worst case scenario you will have to count.

Scott'sF150

Put the rear-end up on jack stands.
Put the trans in N.
Spin one of the tires. If the driver side tire moves the drive shaft when you rotate it forward or rear then you've got a LS diff. If not, then go to the pass. side and do the same thing cuz' you've got an open carrier diff.
Now rotate the tire until the valve stem is at the top of the rotation.
Take a yellow grease pencil or some white out and make a mark that you can see easily on the drive shaft yoke.
Spin the tire 1 revolution and count how many times you see the mark go by.
At a minimum you'll see it go just about 2 3/4 times. = 2.73
Just a hair past 3 times, = 3.08 and so on so forth.

This is a pretty good way to get an idea of your gear ratio w/out removing the dif cover. It's not exact though.