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Kind of looks like a 2 series to me, but it's been a while since I had one. The pic with the tape measure is showing you if it's a 2 or 3 series. The only difference between them is the location of the ring gear flange.
That is where the ring gear flange is offset for the 3 series gears. If you took the cover off of an assembled rear end and looks at the differential the ring gear flange would be on the left side. A 2 series has the flange offset more to the left than a 3 series. The reason is because a 2.77 gear has a larger pinion head than a 3.27, 3.45 or 3.70 gear. The larger pinion head requires the ring gear to be offset more to make room for the pinion gear. The 3.27 pinion head is smaller, and as you work toward the 3.70 gear the head gets even smaller. A 3.27 gear has a thinner ring gear than a 3.70 because of this. Instead of making a different series of differential for every gear ratio they just use 2 or 3 different ones and then tune it with the ring gear thickness. The Chevy car and truck 12 bolt have 2,3 and 4 series differentials. Most others only have a 2 and a 3. Ford only uses one differential in the 7.5, 8.8 and 9 inch for all of their gear ratios, but they have some very thick ring gears when you get into the 5.xx and 6.xx range.
Last edited by big gear head; Apr 13, 2016 at 08:11 AM.
