Sit the diff assembly on the ring gear side (shallow half of the clamshell on the bottom) and leak test the assembly. If you had pre-load problems but have cased no great amount of damage then your diff should seal OK in this position. You'll need a dial indicator long enough to touch a ring gear tooth through your filler plug. Not too sure what Toyota was think'in here...but it's not so bad once you get used to it. The most important thing is to make sure you've got at least 0.7mm of Air Locker shims between the factory master shim and the seal housing bearing cup to make sure you don't get contact between the bearing cage and the master shim. Also you need to make absolutely sure that your bearings are pushed all the way down. Air Locker's are generally harder to push bearings onto than factory diffs as we tighten up the fit a bit to account for harder use of the vehicle and more torque transferred through the bearing. You'd be amazed how many times I get calls from guys who have noisy diffs who simply didn't push their bearings all the way on...and then on the trail they get pushed the rest of the way. Makes for about negative 0.5mm worth of pre-load most times. -hahaha You need to see if you have this problem before you tear the diff apart too much. Check your backlash with the diff sitting on the ring gear side so that any slop (negative pre-load) will be holding the diff away from the pinion. Then try to check it upside down so that the gears sit against each other. If the unit has even neutral pre-load there will be absolutely no difference between the 2 backlash measurements.

If you find a difference then scrap your backlash measurements, open up the assembly and re-set-up the backlash and preload from the start. If there is no difference, then record the backlash measurement, open up the diff (with the diff sitting on the ring gear side (filler plug facing up) and carefully pull the diff upward and free of the seal housing. Inspect the bearing cage for any for of damage that looks like contact with the master shim. Clean the silicone/gasket goo/whatever from the flanges of the clamshell and put them back together. You should be able to get a 0.25mm [0.010"] feeler gauge all the way around the clamshell between the flanges. If not...not enough preload. Remove the seal housing by unscrewing the center compression nut from the outside of the housing, and pulling the end of the tube free. (don't lose the little O-ring inside) Then press the seal housing/bearing cup out. Measure the shim between the factory master shim and the bearing cup. Again, we're looking for more than 0.7mm [.025"/.030"]. Remove the bearing cup from the seal housing. Add about 1mm [0.040"] to the shim to the shim pack, but measure the amount you are adding as accurately as possible. Then just sit the shims and bearing cup in the clamshell, sit the diff into that, and close the clamshell. Measure the distance between flanges all the way around again. Take that measurement and subtract the thickness of the shim you added. That's your actual pre-load. If it's zero or negative, then you're lucky you pulled the diff when you did. Set the pre-load to 0.25mm [0.010"] and hand-bolt the shell together and check the backlash (0.005-0.012). If you're unlucky then you will have to transfer shims between the 2 ends of the diff to get the backlash within range.

Oh yeah...while you're inside there, make sure you haven't hurt the running surface of your ring and pinion set. And closely inspect your O-rings for damage or any helical impressions on the surface which would be caused by sitting the diff center into the seal housing without oiling up the O-rings.

Courtesy Daniel Bongard, ARB.

Synopsis by Lars Dennert: The basic idea is to first look for problems like zero preload and/or backlash specs. The next job is actually to get the preload correct working in relatively small steps. In other words 0.010 around the case. After that, swap shims from side to side to get the backlash spot on 0.008.