12 bolt rear axle questions

[1971 cheburban]

I've got a 12 bolt in my 71 c10. My truck was cut in half and a suburban frame welded to it. So the 12 bolt is from a suburban, not sure what year, with a stack of leafs. I've seen the 12 bolts that are originally in these trucks that have the trailing arms and coils that have the tracking arm mount cast into the housing. but mine doesn't because it has leaf springs. Is that the difference between what they call the "CAR" and "TRUCK" 12 bolts, also is there any way to check for posi without pulling the cover, like jacking it off the ground and spinning one tire and the other will spin with it or what?

[19Chevy67C10]

Jacking the vehicle off the ground will only tell you what gear ratio you have. Other question about the car and truck 12 bolt, Iv'e heard numerious guys say a car 12 bolt is stronger than the truck 12 bolt, this is because the pinion has a larger diameter...I have never checked this out myself but believe it's true due to the different ring and pinion sets for car's vs trucks, they are different...So a car ring and pinion will not fit a truck housing vice vs...I also know that with a 3 series carrier you can only run 3:42 and down gear sets, Richmond does make a 3:73:1 for the 3 series carrier but I wouldn't reccomend it. I would just upgrade to the 4 series carrier which will allow you to run 3:73:1 gears and up...If you look on the back of the pumpkin or carrier housing you might/may be able to find an aluminum or stainless tag that has the differential info still attatched to one of the cover bolts. Hope this kinda helps....God Bless...

[19Chevy67C10]

Also some car 12 bolts still had the panhard bars...

[Ironangel]

The car 12-bolt had a distinctive "eyebrow" stamped across the top of the cover. The truck 12-bolt never received the upgrade given to the car 12-bolts that came into use in 1965 to 1972. The car 12-bolts had larger ring & pinon gears with 30 spline axles. With a couple of upgrades, they were indestructible and would outperform the 9" Fords. "Legendary!" The easiest way to tell a LS (Limited Slip) from a non-LS is to pull the cover. When a LS is working correctly, both wheels turn in the same direction when jacked off the ground. A non-limited slip will turn the wheels in opposite directions when jacked off the ground. A Posi unit will have a distinctive spring assembly visible between the spider gears.