62 rear axle ID help needed

[Mark B.]

While doing some underbody cleaning and detailing I revealed the rear axle housing ID numbers under a build-up of grease. The housing has a vent line and a Positraction metal tag is located under the filler plug on the rear. The numbers stamped into the right side of the housing are "AB 9 24". The cast numbers on the driver's side are 1 or I 178 and under these are 3725899 GM. I can't seem to run these numbers in the Noland Adams book. Any help would be greatly appreciated.

[Joe L.]

Re: 62 rear axle ID help needed

Mark-----

The casting number of GM #3725899 identifies the case as a non-posi unit originally used for 1957-62 Corvettes and 1957-64 passenger cars. The "AB" code indicates a 3.36:1 ratio originally used in 1958-64 passenger cars. The Corvette and passenger car differential units are interchangeable. Given the date code, I'd say that this unit originally resided in an early 1959 passenger car with automatic transmission. That's not to say these gears are what's in the case today; that's just what was originally inside this case. That could easily have been changed "along the way".

[Dan A.]

Re: 62 rear axle ID help needed

I believe 3725899 means this diff started life as an open or non-posi rear end. This casting was in use from 1957 through 1964 for non-posi rear ends.

I suspect your cast date is I 17 8 or September 17th 1958 which works with an assembly date of 9 24 or September 24th. The AB and the single digit year cast date indicate the diff was manufactured at Detroit Gear. AB also denotes a 3.36 open differential in a passenger car with a Turboglide transmission.

Dan, in the cool clear north where it's always 80 degrees and the palms gently sway.

[Mark B.]

Re: 62 rear axle ID help needed

Thanks guys. As always, the numbers tell the truth!! I suspect that somewhere along the way, someone installed a higher gear ratio out of a passenger car into the existing axle assembly. Checking back thru my records on the 59 in my other garage bay, I found that it too had an "AB" rear end installed. Fortunately, I was able to find a 59 date coded Posi unit for replacement. The search will be on for a 62 in the future.