replacing 3.73 12bolt gears

[man-a-fre]

I have a original 12 bolt 3.73 posi rear in my 72 blazer 4x4 that the gears are bad,a friend gave me a 76 4x4 12bolt 3.73 gear rear with an open carrier.Thought the gears would be an easy setup but to my suprise the pinion teeth part on the 76 was larger in diameter and the ring gear was thinner than my 72 originals so it was going to be alot tougher swap than i thought.What year gears are the same as what i have or is it that the posi verses open carrier is the difference.My gears are original with the gm markings as are the 76 chevy 3.73 4x4 gears i tried.

[Mike C]

Hmmm. I could see the ring gear being a thicker on one because of the case break and some aftermarket gear sets, but the pinion should be exactly the same diameter if it is the same ratio. This is assuming they are both 12 bolt TRUCK gears.

Look on the outside edge of the ring gear for part #'s and ring and pinion tooth count #'s and proceed from there.

Just make sure you are comparing apples to apples as well, meaning that you actually have (2) 12 bolt truck gear sets and not something else.