I am overhauling one of these differentials for a fella that has a '57 Vette under restoration. The third member I have came from that car. It was originally a 3.55 but he wanted to go back with a 3.73. No problem - since the 3.55 gear was worn completely out. Never seen anything like it. Anyway, fast forward to today when I was putting it back together with all new parts. The gear I got was supposed to be for a 3-series carrier. I figured since it was a 3.55 previously that it already had a 3-series carrier in it. After all - everyone knows you can't put a 3-series gear on a 4-series carrier, right? WRONG. I have been researching all night and have only found bits and pieces of information, but it appears that the '55-'56 and maybe early '57 models had a bastard carrier and only 3 gear ratios available, 3.55, 3.70 and 4.11. They all used the SAME carrier. The ring gears were exceptionally thin as it turns out. Then sometime in '57 they expanded the gear ratio selection, starting with 3.08 and on down to 4.56. The 3.08-3.73 (no longer a 3.70) used the 3-series carrier and the 4.11-4.56 used the 4-series carrier. What I can't confirm for sure is whether or not the early axle actually had a 4-series carrier or if it was unique compared to the later 3 and 4 series carriers. These all had 17 spline side gears. Anyone got any input on this? Also - anyone got a usable later style 3-series carrier laying around? I don't even need spider gears, just the carrier.