Moparts Tech Archive

Rear Axle

Rearend Comparisons by DoctorDiff

8 3/4" pinion shaft designs.

Left to right: 489 case 741 case 742 case.

Notice, all pinion shafts neck down to the same diameter at the front bearing area.

Contrary to popular opinion, the 489 case does, in fact, have a 90 degree stress riser just like the 742 case.

Notice, the only pinion that does not have a stress riser in this location, is the 741 case.

Popular pinion designs.

Left to right: Dana 60, 742 case, 489 case 741 case, Ford 9" Chevy 12 bolt truck, Chevy 12 bolt car.

Notice, the popular Ford 9" uses the smallest pinion shaft of the bunch.

For comparison, the Chevy 12 bolt truck, has a pinion shaft diameter 0.060" larger than the 741 case.

Note the factory installed solid pinion bearing spacer, found in all 741 cases.

Rear pinion bearing designs.

Side view of the same line up.

Also contrary to popular opinion, the 489 case uses a smaller rear pinion bearing than the 742 case and the Dana 60.

I included the common M88048 rear pinion beaing found in most 9" rears. Even the Ford "Daytona" style rear pinion bearing is smaller than the 741 offering. Admittedly, the Ford 9" also uses a pocket bearing to support the end of the pinion.

As you can probably tell from this post, I consider the 741 case 8 3/4" to be highly underrated when compared to other more popular "performance" ring and pinion designs.