T-Maxx Differential Shimming

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Whats Needed:

  • 6x9x.5 Teflon shims (# 3981)
  • Tools to remove the diffs from the truck

Lets Begin:

Obviously, you need the diffs off the truck and fully disassembled. Clean all grease and/or oil off of all parts. You need to shim while the parts are “dry” so the grease isn’t adding false width here and there.

From here on, I’ll assume you’ve cleaned everything and have it all apart. Also, you will need a bag of 3981 (6x9x.5 Teflon shims). You can use thinner steel shims, but I didn’t and it worked out fine.

The first part to shim correctly is the actual t-maxx diff itself, which includes the following parts:
diff cup, spider gears, pinion gear/shaft and the bevel/ring gear (parts 4982 and 4981)

Take the pinion gears that goes through the cup and bevel/ring gear and put 1 .5 Teflon washer on both. Assemble the diff together including the spider gears and the shaft they sit on, but you only need 2 of the screws in the cup. See if there is any slop. You want to be able to have about 1mm of slop while turning one pinion gear/shaft while holding the bevel/ring gear and one of the shafts. If you don’t have at least 1mm of slop, take out a shim and retry. If you have more than 1 mm of slop, put another shim on either side(not both) and retry. When your satisfied with the slop, make sure that you can turn both pinion gears in opposite directions without binding. It should be smooth. If you experience a ticking feel or grinding, you’re too tight and need to take out a shim.

Once the T-maxx diff is properly shimmed, you need to shim the slop between the bevel/ring gear(4981) and the pinion(4981) that drives the bevel/ring gear the same way.

Install the bearing in the t-maxx diff case halves that the diff goes into. Put the diff assembly in a diff case half with the teeth facing up. Put a shim on the main pinion(4981) gear, then the two bearings and attach the other diff half. Now the diff should be fully assembled. Push/pull on the pinion gear(4981) that is driving the bevel/ring gear(4981). You should have between 1-1.5mm of slop. If you have less, take out the shim on the pinion(4981). If you have more, put another shim on the pinion and retry.

When you are satisfied with the slop, spin the primary pinion to feel for smoothness. Again, if you experience a ticking feel or grinding, you’re too tight and need to take out a shim.

When you are completely satisfied with the slop on all output shafts and the inner diff assembly, take it all apart while leaving the shims installed where you have them. Fill the inner diff cup with grease, assemble diff. Put the diff in a diff half, fully coat the teeth of the bevel/ring gear with grease and assemble the rest of the diff.

These are the steps I took while rebuilding my diffs with the maximizer aluminum diff cups and modified stock bevel/ring gear. I pulled the diffs apart after 1 gallon of running with a 21 OS RG as my mill. There were no signs of wear on any of the internal gears. I’m now at about 2.5 gallons of fuel and haven’t had any of the obligatory diff issues that the Maxx is known for yet.

Feel free to ask questions about this tutorial in the T-Maxx Talk Forum.