The stock gearing is pretty slow, but there's room for improvement. With the non-proportional controls, its a little hard to control the throttle of the truck. For some stuff going a little faster is fine, but there's a lot of stuff that going a little slower can help out a lot.
Inside the Nylint axles are a set of planetary gears. It just so happens that these gears are nearly identical to the Tamiya Planetary Gearbox that you can buy at your local hobby shop or online at Towerhobbies.com . You will only need one of the Tamiya gearboxes, as it contains multiple gears, enough to do both front and rear axles. I just so happened to have one that I bought previously, so I had to put it to good use!
To get started you need to put together a 5:1 gear set as shown in the first picture. You will put this BEFORE the black gear. (in between the motor and the drive axle gear) In 2nd picture, the grey section is the Tamiya part.
You do have to slightly modify the Tamiya and Nylint gearboxes for them to mate together. On the Tamiya gearbox, there is a small alignment tab on the inside of the planetary ring gear. I used a fresh razor blade to do the cutting. Then, on the outer rim of the black Nylint planetary ring gear, you need to cut off another alignment tab. Then, finally, on the white planetary ring gear, you need to cut off the 3 alignment dowels. Then they will fit together.
You will now need longer screws to hold the gearbox together. The Tamiya kit comes with one set which you will use for one of the Nylint gearboxes, but for the second one, you will have to either find some long 3mm or 4-40 screws, or do like I did. I couldn't find any longer screws around, so I bought some 4-40 threaded rod and nuts from Lowe's (in the drawers with the hardware, not with the other threaded rod) and cut them to length. I then put a nut on each end, added some blue loctite to make sure the nuts didn't come loose, and tightened it back up. You want to make sure you leave as little excess rod at the ends as possible, because its a very tight fit.
Now, you will have to modify your gear cases in order to fit the now longer gearbox. This will also eliminate one of the 4 screws that hold the case together. More on that later. Look at the pictures that show the plastic I cut away. I tried to cut as little as possible, test fitting after each cut.
I might have been too liberal with the clearancing of the axle cases. But I didn't want to weaken anything. As a result, the gearboxes did not close fully after loosing the 3rd screw. So what I did was drill a hole in the top of the axle case, clamp the axle closed, and ran a wire tie through the axle. This closed up the rear axle great, but the front axle still had a small gap. I decided to smear a little black RTV silicone on it to seal things up so no dirt or debris gets in it. I might even go back later and run it all around the axle just to be sure.
The end result is a MUCH slower crawl ratio than stock. It's great. I now have a lot better throttle control. When I let go of the gas, the truck immediately comes to a stop as opposed to rolling a little as it did stock. This gives me a lot greater control while crawling. But if I want I can switch the gears into high gear, which will now have the same ratio as the old low gear.
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