8 3/4 Chrysler pro gears?

[Dwight Southerland]

Originally Posted by Myron Piatek

I read a dedicated article comparing rear end efficiency in one of the old car magazines a long time ago. Of the rears that I remember they tested, this was the order of efficiency:

1) GM 12 bolt
2) Dana 60
3) Chrysler 8 3/4
4) Ford 9"

I believe it said that the biggest factor is the placement of the pinion in relationship to the ring gear. The higher the pinion (closer to center), the more efficient it is. The 9" has the additional disadvantage of an extra pinion bearing.

It's called hypoid distance. Dana 60 is 1.125". MoPar 8 3/4, GM 12 bolt and 10 bolt, AMC Model 20 are 1.50". Ford 9" is 2.25". The farther the pinion is from the centerline of the ring gear, the greater the angle of the drive teeth to the ring gear teeth and more friction. Bearing size is a factor for efficiency as well as rotating mass.
I remember that same article, but have since learned from other sources who have done serious experimentation that the Dana 60 is more efficient than the 12 bolt.