[jkstill]

The FSM specifies that you need to measure both the inside width of the diff case and the outside width of the differential. This is so that you can determine a starting point for shim sizes. If you are using the same diff and just replacing the gears this won't be necessary - just use the shims that came in the diff as the starting point.

When replacing the diff and the gears as I have, the measurements will give a good starting point for shim sizes. Measuring these sounds simple until you try it. A regular caliper will not fit inside the diff case to measure the inside width. If there is a tool for doing so, I don't know about it.

Building a tool to make this measurement was pretty simple. Two small pieces of round aluminum stock, and a 12 inch piece of 1/8" stainless rod were all that was needed. A hole was drilled in each piece of stock to slide the rod through, and a hole was drilled and tapped in the end of each piece so a set screw could be used to secure the rod.

As shown in the pics, the tool was adjusted out to the width of the case, then a caliper used to measure that.

Measuring the width of the diff with bearings and races install is somewhat tricky. I finally settled on using a 1x1x12 inch piece of steel as a straight edge with a torpedo level attached. After leveling the straight edge on top of the diff assembly I measured the height on each side and took an average, which worked well enough. Make sure you are working on level surface.

The math for determining the shim sizes is pretty simple and in the manual. One funny thing about it is that you are supposed to add .002-3" to the diff width to determine the shim sizes. It's funny because the shims only come in .5mm (~0.016") increments.

Next: Install Differential Into Case