Tamiya vs. Yokomo - What’s the Diff?

April 28, 2021

For some time now, there has been a few people who have been using Tamiya gear diffs instead of the Yokomo gear diffs in their YD2s and just about any other chassis that accepts that style. I would say until recently it’s been a pretty well kept secret, but recently it seems to have become really wide spread knowledge. I want to credit Allen Shilun Gu (Sensei) for this helpful tip. I will go on record right now and say he is one of the most innovative tuners I have had the pleasure of knowing.

When using a gear diff, different fluid weights are used to achieve more or less diff action between the left and right rear wheels. The effects of this goes deep enough to to warrant it’s own write-up, so we won’t go into detail here. This is just meant to show the difference between the two.
What most people are unaware of, is the diffs themselves introduce their own resistance just due to the design, materials used, tolerances, etc. The less resistance created by the diff itself will mean the change in fluid will have a greater and more consistent effect on the diff action itself.

Both Tamiya and Yokomo have a very similar design and are interchangeable for the most part. I have only seen 1 instance where it didn’t work, so make sure to check before taking the plunge. The Tamiya diff is about 1.2mm narrower, so I put .6mm of shims on either side before installing the outer support bearings to keep everything nice and centered. I have also been in the habit of using the Tamiya upgraded drive cups with the plastic inserts. It just seems to be the best setup for me. The upgraded drive cups are 2mm shorter than the Yokomo, so this may or may not require you to get longer driveshafts. I personally have not found this to be an issue yet.

To clarify, this is NOT to demonstrate how to get the freest spinning gear diff. This is to show if you are tuning, the diffs introduce their own resistance before you even get started. For example, you can still tune a Tamiya diff with lower viscosity fluids and still control the amount of resistance you have, where as with the Yokomo you will find it no longer makes a difference at a certain point. If you start taking out gears and O-Rings and such, everything is out the window. An old trick to get a free spinning gear diff is to remove the O-Rings. You will lose the ability to tune your diff with fluid since it will all leak out, but it will be more free. Removing spider gears will also make it more free spinning. Again, this is not what this is showing. If I find the sweet spot with a Tamiya gear diff with 2500 fluid, I will not be able to get that same setting with the Yokomo gear diff since the Yokomo effectively stops at approximately 10,000 in the Tamiya. Is completely free spinning the best? Hmmm.

Rather than to try to show the difference with a series of pictures like I usually do, I have made a short video clip to explain here. I built both diffs the same and I used the same light grease I always use on both.
Link for Tamiya Gear Differential here:
Link for Tamiya Upgraded Drive Cups here:

I hope this can help to show why so many are doing this, and what the difference really is.
SEE YOU ON THE TRACK!