Decided to take some time to try and help everyone out with building your gear diffs! I was lucky enough to be running for Serpent when they introduced the first one into a competition TC and it was pretty cool being able to pass the other racers with ball diffs right off the grid! The downside to gear diffs is that you can't just loosen or tighten a screw and have a different feel, ideally you want to have a few built up for different track conditions. One thing that few people pay attention to is making sure that you build it the same way every time! If you have a diff full of 3k oil it can have a thicker feel than the same diff half full of 5k oil. Take a little extra time here and it will pay off.
A good condition used diff is going to feel better than a brand new diff. One of the 3 I'm putting together here is used, I am replacing the pins and shims (31348) and the o-rings and diff seal (31349) because the diff still feels great but I want fresh oil. Keeping the bevel gears for as long as you can doesn't hurt because they are now fully broken in and will be as smooth as you can get them.
If you are building a new diff take a moment to cut off the small amount of material on the back of the gears left from the original moulding tree, you want the back to be perfectly flat.
When installing the outdrives, rub some black grease over the shaft after installing the small o-ring that sits in the groove, make sure to apply the grease across the whole shaft so that you don't damage the larger o-ring when installing the outdrive into the diff housing.
Even before running for AE I have been using their shock and diff oils. Inconsistency has always been an issue with oil, but I trust that Lucas Oil is going to do a good job of making sure consistency stays the same from bottle to bottle over time, and that's who supplies AE's oils.
Get everything installed and fill the main housing with oil to the top, turn the outdrive a bit to help guide the oil down and then refill to the top. At this point I put the diff into a shock air pump and pressurize it to remove any trapped air. You'll have to do this a few times and as air pumps out just keep refilling the oil to the top of the diff housing.
After repeating a few times you can see that my diff is full of oil with as little air as possible.
I push the last gear into the others in the main housing and line up the pin slot with the pin on the second half of the outdrive. I also fill up that second half with oil right about level with the metal shim.
Assemble your diff and tighten the screws in a star pattern and try to get them all tightened down with the same amount of pressure so the gear doesn't wobble and the diff doesn't leak.
Now here's the crucial step that often goes overlooked. Weigh your diffs! As you can see this one comes in at 22.3 grams, and this is exactly what I will build the others to. Take your time and get them as close to each other in weight as possible. Any diffs you build for your 6.2 from here on should have the same weight as the one you just built. (Unless the materials are changed which is still no biggie, just build up a new benchmark diff for yourself.)
These 3 are ready for the track!
P.S. sorry for the crappy lighting, hope this is still helpful for everyone!