12 BOLT REAR END

[escadave]

Hey guys, wanting to swap out my rear end for something with better gears. Looking to go to a 3.73 limited slip. 12 bolt would be awesome but chances finding something would be slim. Anybody know any vehicles that would have this set up stock? Thanks!     

[Captkaos]

What year is your truck?  There is no way to tell what is in an axle as far as gears without pulling the cover.   12 bolts were offered from 73-82. Limited slip was an option as was the 3.73 gears.

Chris Lucas
73-87chevytrucks.com
squarebody.biz

[gwcrim]

Isn't there a tag on one of the cover bolts that has the gear ratio on it? (If it hasn't been removed.) 

You can tell the ratio by spinning the yoke.  If both wheels spin the same direction, it's a posi.  In this case, count the revolutions the yoke takes to spin the axles once.  If you turn the yoke and the wheels spin opposite directions, it's an open diff.  You'll have to hold one wheel still and count the turns the other takes.

At least, that's how I've done it in the past.

[gwcrim]

Didn't most trucks come with a 12 bolt?  A truck 12 bolt, not a car 12 bolt.

I had a local mechanic pal put a 3.73 posi in mine.  I think I had $5-600 in parts and paid him $2-300.  I'll do most any mechanical work myself, but setting up rear end gears I leave to someone with the right tools and some experience. 

Doing it all new might be more expensive but its a lot of work to swap one out and a howling rear end really annoys me.

[escadave]

It's an 83

[roundhouse]

10 bolt is just as strong as a 12 bolt
Only way to know ratio is spin the yoke and count turns


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[Captkaos]

Spinning the yoke will give you an idea of the ratio.  3.23 vs 3.42 isn't easy to decipher by spinning the yoke and counting turns.
Both axles spinning could be two things.  Someone welded the diff (bad) or it has a limited slip
one axle spinning could be two things,  worn out limited slip, or open carrier..
The only way to determine either with 100% accuracy is pull the cover and get the numbers off the ring gear and visually see if there is an limited slip.  Plus it probably will be the first time it has ever been removed...

I listed the years for 12 bolts above but again from the factory
12 bolt = 73-82
10 bolt = 80-87