I will be picking up some factory 3.91's. Looking for GM posi to go with these GM gears. Thanks.

Matt

 

Depends upon if you have an O-Type with HD 31 spline axles or a standard 28 spline axle rear.


Info from Brian Trick:

Here is a list of the posi units & what gears they will fit:
#673 = 2.56 & 2.78 ratios, 28 spline
#671 = 3.08 & 3.23 ratios, 28 spline
#588 = 3.42 & anything numerically higher, 28 spline
#672 = 3.42 & anything numerically higher, 31 spline

 

I may build it with aftermarket axles. So open to either posi. May have located one today. Thanks.

 

My understanding is the housing for the 31 spline axles has larger diameter carrier bearings than the 28 spline housing, so if yours is an original 28 spline housing then I don't think you can fit a 672 carrier in the bearing saddles/caps.

 

PM sent.
Derek

 

Posi found. Thanks guys.