Since returning to the blue team in February I’ve had some trouble with the tamiya gear diff unit II. At TITC Kiyo gave me a run down of how he builds the diff, very simply he trims the gears and adds 0.3mm shims on the long side and 0.2mm on the short side. I tried this and had my washers cone quickly, like after 2 runs. To be fair RC Addict was SUPER high grip and I was running boosted 4.5. He suggested using the small outer diameter shims but I had these collapse even quicker.

So I started looking for a solution and to date this is the best one I’ve come up with. What I like about this fix is that it’s really easy! You’ll need:

• 1 x Tamiya gear diff unit II
• 2 x 5x10x0.5mm shims (the OD probably doesn’t matter, up to 13mm fits)
• 1 x gasket (additional)
• Sandpaper

So here are all the parts, I’m rebuilding a diff which is why the stuff is used. The gears have been trimmed from the parts tree and the flashings removed, but they have not been sanded.

You’ll probably find that the 0.5mm shim will fit off the bat, but it will be too tight

We want a tiny amount of play in the outdrive, so we’ll need to sand the outside of the case to allow the outdrive to sit a little deeper into the diff. I’m using 800 grit here, and it doesn’t take much effort to remove the required amount.

Once you have a bit of play, this side is ready. My play is approx 0.1mm.

Now for the other side. The big side is harder to keep square as you sand, so it’s best to take it slow

Now for the double gaskets. This is required because by sanding the outside of the case and using bigger shims we have brought the gears closer together. Thankfully we’ve brought them in by about the thickness of a gasket. I use associated green slime on my gaskets, but TBH it’s gonna be pretty tight so you may not need it

OK so I mentioned it’s got to be tight! Tighten the screws in a star pattern and keep tightening until you basically can’t tighten them anymore. Tighten each screw a little at a time. Once done check the backlash between the gears, you should have a tiny amount of slop and the diff should feel smooth and not at all “geary”

Now you’re ready to go. The reason we tighten the diff so much is to a) get the mesh tight enough, and b) ensure the diff fits between the bulkheads – because we added an extra gasket we’ve made the diff physically wider, so we need to crush the gaskets a little.

Note: after being so tight the gaskets will be unsuitable for use on their own in a single gasket diff. Gaskets are cheap tho, and this mod should stop you from DNFing

Edit: The shims I’m using are from http://www.smallparts.com.au, which is an Australian retailer. They are carbon spring steel so they are very strong, and they cost next to nothing when you buy a reasonable quantity.