Tamiya #42313 Large Shim Set for Gear Differentials

But first, a little background…

Effectively, I haven’t been racing for the past 3 years. Personal circumstances and choices meant I could’t attend club races regularly, and because I wasn’t racing regularly, I felt less inclined to attend the bigger events.

Last year, I tried to race in the Iconic Cup, and for whatever reason I had lots of problems, and didn’t achieve what I felt I should have done.

This winter, I tried again with the CWIC XRS (run by the Chippenham club). Again, lots of problems with the car, combined with being well off the pace.

I would be intrigued to know what is the root cause of the problems – lack of practice, my increasing age, outdated equipment, or simply a lack of motivation. Sadly, I don’t know the answer.

What I do know (and this is what leads me on the the real topic of this post), is that if you under-perform, you end up in races that you shouldn’t be in, where driving etiquette appears optional. And you get battered.

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I am still running my Tamiya/Samix TRF418 with the 419 rear diff. It is a car I have struggled with on many occasions. As the winter progressed, I managed to get a degree of consistency out of it on the new-to-me Hudy tyres and ETS carpet. Unfortunately, consistency doesn’t count for much when you get punted repeatedly by lapped traffic.

The rear diff broke – breaking an input gear and coning the shims.

While searching for some replacement parts, I spotted these:

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The set includes 2x 0.3mm shims to go behind the input gears, 2x finer 0.1mm shims for the same location, and 4x 0.1mm shims to go behind the spider gears. As these shims are the same size as the gears themselves, loading should be much more even, reducing the tendency for the shims to cone. Also, the large size should make it harder for oil to find it’s way through the seals, reducing leaks. We’ll see if this works out in practice.

In terms of re-assembling the diff, I always shim the input gear so that it rotates smoothly with minimal backlash. Just one 0.3mm shim was enough for this on both sides. I will reappraise the shimming next time I have the diff apart.

I also put a 0.1mm shim behind each of the spider gears, and assembled the diff dry to make sure everything worked smoothly, again with minimal backlash. It did, so I filled the diff with oil (#2000 for now) and put it back in the car.

I have to say that I don’t buy in to any of the diff-building “voodoo” that you may read about elsewhere. Tamiya’s parts are fundamentally good quality. I don’t sand down the gears, I don’t weigh the oil, I don’t use special slime on the seals. I just lube the seals with the normal silicone oil, make sure there is no flash on the gears, and fill the diff until the fluid sits just above the cross shafts.

Plan is to get this on the track again this week and see if it runs properly again. Will be glad to put this winter’s racing behind me!

 

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