I have a1967 Chevelle SS with a 4:11 posi-trac. I have not pulled the cover yet, but I need to know if this differential has a big carrier with these gears will I be able to go back to a 3:31 or 3:23. I know that if it had a small carrier you have to use a spacer to go to a 4:11 from a 3# gear. :confused:

i'm not sure, but i think that carries change sizes at 3.9 gears. Below that being the smaller carrier, above that being bigger? Anyone else want to chime in? Might want to put this topic in the trans forum.

Ya you need to have a 3 series carrier for those gears 3.07-3.73. You have a 4 series now.