I bought and 88 tin top and convinced the owner to throw in extra axles and two differentials I saw laying in a pile. She has 31's and not much of 5th gear. I am hoping the diffs in the axle housings or the other diffs are geared higher but am not sure how to check the gearing... Who knows the secret?

No secret - count.

You can either pull the third member & count the teeth or find a way to lock one axle and turn the other - with an open diff you can lock one axle and count the number of turns of the other axle it takes to turn the pinion once, divide that by two and you'll ahve the ratio.

Thanks, going from memory-third members in the back of a wharehouse at work- you can only see the ring and not the pinion (or visaversa). They are covered in light rust, you think a good oiling and change the axle fluid after 100 miles would keep grit from causing problems?

Thanks, going from memory-third members in the back of a wharehouse at work- you can only see the ring and not the pinion (or visaversa). They are covered in light rust, you think a good oiling and change the axle fluid after 100 miles would keep grit from causing problems?

You got me there - so count the turns.

I'd certainly coat them with oil to protect them from further rust, but I'd be tempted to strip clean & reassemble with new bearings rather than risk ruining them.

count ring gear teeth
count pinion teeth
divide...