cmerrick

What is a 74 C3 differential? I'm assuming it's based on a GM 10 bolt? I've tried looking through numerous documentation sources and haven't found anything.

Gordonm

It is a 10 bolt but the Vette is unique and it is used in no other car. They are the same from 65-79 Vettes.

GTR1999

It is corvette specfic. It is a 10 bolt unit. The 63-69's were open - posi was an option. 70-79 were all posi. The early posi's were Dana's I believe, the Eaton unit appeared in 65 and it is not as good as the 69-79 units. The clutches were better but the spiders and case were not.
The side gears use 17 spline yokes also unique to corvette. The yokes are held in with a snap ring not c clips or e rings as I see mentioned here a lot. The yokes on the 75-79's were much softer then the early cars and typically are worn out by now. The ring gear bolts used the 63 to the mid 76's were replaced with flange head bolts and they backed out a lot and locked up the 76-79 differentials.

Does this help? I see you're in Belchertown I used to service milling machine up there many years ago, nice area if I recall.

cmerrick

Great info. Thanks. We were at the Stafford swap meet this morning and there was a set of 10 bolt 3.73 gears for $75. Almost picked them up until one of my friends cast doubt saying he thought they were Dana 44 based. I know the Jag IRS is Dana 44.

Belchertown is nice, but it's getting to be a bit expensive if you want to move in now. We've been here 18 years.