54875 Tamiya TT02 Oil Gear differential unit Review

Tamiya has been supplying oil filled differentials with its TRF and Club racer spec chassis for several years. Unfortunately TT02 racers ...

Tamiya has been supplying oil filled differentials with its TRF and Club racer spec chassis for several years. Unfortunately TT02 racers were have not even been given a hop-up option to upgrade their differentials, until now.

For the uninitiated, oil filled gear differentials have superseded ball differentials in 1/10 onroad, for some of the following reasons.

  • More direct on high punch than a ball differential: There is always an inherent amount of slip on a ball differential
  • Less maintenance: they are sealed so no dirt and less moving parts. So you are fine over several meetings, with no pressure to rebuild after every race.
  • More consistent over an event: Ball diffs can loosen, dirt can get in them etc, These diffs are sealed.
  • Easier to rebuild - Once you find your preferred oil thickness, you simply replace the same oil in the differential to make it feel the same.

So let's take a closer look.

The package contains the differential case, internal gears, gearbox joints, a pot of 3000 silicon oil, Bearings, o-rings and a gasket.

NOTE - The first thing I must let you know is that this differential is not going to work with the standard plastic TT02 chunky drive shafts. If you want to run these differentials you will swap out the plastic dogbones for the Tamiya 53792 Assembly universal drive shafts.  If you have a TT02-S, TT02-R or TT02-RR you should be fine as these do not come with the plastic dogbones.

When you start building the differential you first want to coat the two 5mm (thin) o-Rings. You can use a drop of the included 3k oil to lubricate them, however I used 1up Blue o-ring grease as if find it really helps reduce friction and also works well to stop any leaking.

You need to place the bearings on the case before inserting the gearbox joints.

Now it's time to add a drop of grease onto the gearbox joint and push it into the differential case and ensure that you slide it into the lubricated ring. Use some tweezers to push the ring back into position if needed.

Now you get onto the most frustrating part of the build, you need to place the pin through the hole in the gearbox joint. You need to use tweezers here but there is still not a large amount of space, I found moving the pin into the corner to be the easiest way to do this, then push against the joint as you rotate it slowly until it locks into the hole.

After a bit of fiddling you will hopefully be able to thread the pin through and you will be able to relax and move on as the rest of the build is really easy.

Its time to add the internal bevel gears now. They are made from steel, not my preferred material as plastic is more than adequate for onroad. The steel gears weigh in at 8.44g which is twice as heavy as the TRF differential internals (A combination of plastic gears and aluminium diff axles).

The large bevel gear goes onto the pin

Now we put the two smaller gears on the diff axle and slide it in and ensure that it is seated down on the large bevel gear. It's time to add the oil into this part of the differential.

When filling a gear differential it is always best to weigh it. This ensures that you are filling it with exactly the same amount each time, essential to maintain the same settings between services. Tamiya recommends to fill the oil so it covers the centre flat spot of the diff axle. I took my time adding the included 3k oil to this setting (Fill it slowly, to avoid air bubbles and to ensure that oil seeps into every office).  The final amount of oil was 1.7g

Whilst leaving the other half of the differential to ensure their was no air bubbles I worked on the upper Ring gear half. This is much easier as you can fit the pin very easily into the gearbox joint. I used some AE green slime around the edge of the ring gear, it is great at supporting the gasket to stop leaks on the outer edge.

I used tweezers to fit the gasket in place, the green slime helped it stay in place and then mounted the final large bevel gear.

The two halves are now connected, it all slots neatly into place and you should be able to twist the top gearbox joint and see the lower one move, ensuring the gears are all meshed together neatly.
Add the four screws in a cross pattern to ensure that the top ring gear does not get warped. The plastics used on the differential are glass re-enforced plastic, so they are strong, but the molding is great and the screws were easy to attach.

The final differential feels quite smooth.

The final weight is 31.04g. The steel internal gears and gearbox joints contribute over 18g of the final weight. So at some point I will see if there are any lightweight alternatives to hop-up the diff.

Now it's time to fit it into the TT02. Tamiya supplies a replacement bevel pinion gear to replace the kit one. I cannot actually see any difference with the teeth profile, but it comes included in the bag so I swapped it out as per the instructions.


Running at the track the differential has been flawless and very smooth. The extra weight is something that is easily compensated by the more consistent handling and ease of tuning possibilities. This differential is actually one used in the Tamiya TG10 Mk2, so spares are able to come by if you need them, although because of it's nitro heritage I would think that it will hold up to a lot of running.

The main negative for me is the metal internal gears, and the gearbox joints are narrow and not made for drive shaft cushions. However these are me being picky, as I am used to the units that I have in the TRF cars.
TT02 2922278009752570852

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