1968 HD Rear diff. Questions

[Rodney Armstrong]

I have a 1968 rear differential that is coded AW. From what I gather this is a 3:08 ratio Heavy Duty. What is the difference between the heavy duty and the standard differentials? What is the lowest gear ratio that can be installed in this housing?

Thanks for the Help, Rodney Armstrong NCRS# 33231

[Joe L.]

Re: 1968 HD Rear diff. Questions

Rodney----

The only difference between "standard" and "heavy duty" differential assmblies was the side yokes originally installed in the unit. "Standard" differential assemblies had yokes which utilized u-bolts for u-joint retention. The "heavy duty" assemblies used yokes which used forged caps secured with bolts for u-joint retention. The "standard" assemblies were used for most all small block applications from 1963 to about 1971. After 1971, or so, some some blocks were built which used the "heavy duty" assembly with cap type yokes. However, as far as I know, there was no predictability to which received the "standard" and which received the "HD". although it may have had something to do with transmission usage. ALL big blocks from 1965-74 used the "heavy duty" differential assemblies.

The 1963-79 Corvette differential housing assembly will accept any ratio between 2.59:1 to 4.56:1 and, likely, even numerically higher gear sets. However, the positraction carrier cases are different for 2.59:1 to 3.70:1 and 4.11:1+ ratios. Of course, the 63-79 Corvette differential ring and pinion gearset is unique to Corvettes, so only Corvette-specific gearsets can be used. All of the GM Corvette gearsets are discontinued. Replacements are available from Richmond Gear and, from time-to-time, U.S. Gear.

[Jim Trekell #24375]

Re: 1968 HD Rear diff. Questions

My 70 original owner has the "heavy duty" rear end and 3:08 gears. When it became known to me that I didn't have the standard rear end I began wondering why my 350/300 HP car would have this set up. I wonder if my car had a 4-speed instead of the Turbo 400 automatic would it of had the standard rear?

[Jim T.]

Re: 1968 HD Rear diff. Questions

My NCRS member number is wrong on previous post.