Hey CL family, as of today my AT SC300 diff finally arrived at my house, and after I got off of work, I got straight to work on it. When purchasing a diff online, you never can be entirely sure that you are going to get exactly what you paid for, so I’ll be going over a few of the things I did to verify that my diff indeed had a 4.27 gear ratio. The first thing I did was take note of the letter and number sequence on the diff cover, seeing as there was no ID tag. My cover read F2OSZ 1-1. I tried searching through the forums here, but all I could find was that a F2OSZ 1-2 was from a MT SC300. Keeping that in mind, I’d drawn the conclusion that the F2OSZ 1-1 was from an AT SC300. But, I still wanted to prove this theory. I was going to be opening the diff anyway, so I thought I’d check for stamping on the ring gear that would indicate the number of teeth on the ring, and pinion gears. When I’d spun the ring gear around 3 full rotations with no signs of stamping, I knew I’d have to do this the old fashion way and count the teeth myself. The ring gear counts 47 teeth and the pinion gear counts 11. Taking the 47 ring gear teeth and dividing it by the 11 pinion gear teeth gives you a final figure of 4.27; just what we were looking for! Now that I’ve confirmed the gear ratio for myself there’s only two more steps that I personally have left; cleaning, and welding the diff. I’d like to give a huge thanks to everyone here on CL for providing me with the knowledge needed for current and future projects, and I hope I can do my small part for the community and help a few of you guys out with this thread.