??? GU6 is the axle code what are the next three? That will tell you what manufacturer.....Google!
The rear axle ratio, differential type, manufacturer, and build dateinformation is stamped on the right axle tube (as viewed from the front of the car) on the forward side... a real b*tch to see when it's still in the car. The first 3 digits indicate the axle code, the next one indicates manufacturer (B=Buick, O=Olds, C=Chevy, P=Pontiac), the next is Julian date it was built and the last it the shift it was made on. Limited slip rearshad a tag on the differential cover that stated it need posi fluid... that's usually missing, if the cover has ever been off. However, a "B" in the axle code (i.e., 2BX) usually indicates a posi.
The 7.5" rears have a differential cover that is smooth and kind of a squared off oval shape. The 8.5" rears have a rounder shaped cover with a raisedhorizontal area in the middle.
http://www.gnttype.org/numbers/axcodes.html
