[b-man]

On the GM rear ends being discussed here the differential contains the spider gears and side gears (and sometimes posi clutches too), the ring gear bolts to the differential. The differential unit installs from the back with the pinion gear already in place in the housing. This type of rear end where the differential loads from the back is known as a Salisbury design.

Same differential definition applies to the Ford 8" & 9" rear ends except the design of that rear allows you to remove the differential/ring gear assembly along with the pinion gear from the front as one unit making for easier gear changes. The Ford rear ends like this are a Hotchkiss design.

The '55 -'64 big Pontiac 9.3 rear ends as well as the '55 -'64 8.2 Chevy rears were all Hotchkis. The later Ford 8.8 rears are Salisbury.

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In order to accomodate different gear ratios the differential unit needs to be able to accomodate the different gear ratios. Sometimes a new differential unit with an offset flange to mount the ring gear is needed to do this, hence the 2 different differentials for the GM 8.5 and 3 different ones for the GM 8.2.

A 2.56 gear has a very large diameter pinion gear compared to the pinion on a 4.10 gear. The ring gear will be offset further to the side on a 2.56 rear than on the 4.10 to accomodate the larger pinion gear diameter. In the case of the GM 8.5 the 2.41 & 2.56 will work on one design, the 2.73 and higher gears numerically will work on the other one.