Hey y'all, I have a 1980 Chevy shortbed truck frame complete with IFS and a 12 bolt rear end. I got it for next to nothing from my neighbor. I was going to use it under my '51 F-1. But since that is gone the frame needs to go too. I did a quick glance at ebay. Posi rear ends obviously go for more $$$. Before I post this for sale, how can I figure out if it is Positraction and what gear ratio it is? Any help is appreciated. Thanks in advance. -ejk
Without pulling the cover off, you can't... sorta. You can spin the axle one full revolution and count how many times the yoke spins. If it spins 3 times its a 3.00 to 1... if it spins 3 1/2 its probably a 3.55 to 1... 3 3/4 times a 3.73 to 1 etc. Not perfectly accurate. The best way is to pull the cover off and count the teeth of the gears and divide the ring gear into the pinion (ie 41 divided by 9) that will give the ratio. For a posi? You just spin the axle and see if both sides spin together. If the opposite side goes backwards, its not a posi. You might need some resistance on the opposite side. Keep in mind, that if both spin in unison, it doesn't mean its a posi... it could be a spool or someone welded up the spider gears in an open rear. Its best to yank the cover to make sure. Whoever buys it will probably open it up anyways for inspection... just do it!
look on the axle tube on the pass. side between the spring and center housing. there will be some munbers and letters stamped on that axle tube. most of the time it is facing toward the front on on the top. pm me the three letters and i'll look it up for ya.
as for the posi thing...the guvlock rear was common in those, it will spin like an open rear, you have to pull the cover. is it 5 or 6 lug? they made them both ways, for 2wd and 4x4
Look at the little tag hangin' off of it. Unless of course they quit puttin' the little tag on 'em by then, should have a tag my '88 had one, and my '65 still has one on it.
Not to rain on your parade but the truck 12 bolt is a very common rear that usually don`t bring the money that say a 12 bolt for an a-body car would. Truck 12 bolt posi around these parts are 100-150.00 all day long. A 12 bolt posi from say a Chevelle would fetch 350-500.00! FWIW
Once you have the numbers you could also visit the American Casting Numbers Club to id your rear. www.aancclub.com
Raise one wheel off the ground. If you can easily rotate the wheel without the other one moving, chances are very good it's an open rear end or an extremely worn posi. In order to get an approximation of the gear ratio you will need to rotate the raised wheel 720° (two full turns) while counting the number of turns of the yoke. 3.5 turns would indicate a 3.50 ratio, etc. If it's a posi and the wheels turn together, you only need to rotate one wheel 360° to get the ratio, as the other one will follow and contribute the additional 360°.
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