I'm looking at a 12 bolt rear for my '57 that has the following numbers on it. CON 3 - which looks like a gear ratio/differential type code, but I can find a match for it. Then there's: 67 * 90 - the star isn't really a star, but there's a mark in between the 67 and the 90. Then there's B 121. The other number 3969278 NF, I know is a Chevelle code. Does anyone know what ratio/differential (posi/non-posi) the CON 3 stands for? Thanks.
CON3 doesn't have anything to do with the ratio. The B 12 1 sound like the date code, which would make it a 1971 rear, if it is indeed out of an A body.
CON 3 means conveyor 3, I think.....although I know little about how foundrys work. Generally if you want to figure out what the ratio is and whether it's limited slip or not, you just have to turn the pinion and count the turns to get both axles to make one exact revolution in the same direction. and if you can turn the axles independently, then it's not posi, if they both want to turn together the same way then it is posi. The code numbers you're looking for are NOT on the cast center part, they are stamped on an axle tube.
More often than not, on the top of the passenger side...these were hand stamped, so don't be shocked when it is crooked, and the pivotal last 3 numbers are either very faint, or not there at all. When in doubt, yank the cover. it MAY be a rear end from an olds-which did a fun trick-12 bolts on the outside, 10 on the inside. (and yes, it still showed up in the early 70's. Ask my Vista Cruiser...)
like they said it's on the right axle tube. it will be some letters and numbers. what we need are the two or three letters. that's the code. pm me the letters and i'll look them up for ya!
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