Hotshot 2/Boomerang Rear Control Arm Conversion - How to Guide

[MadAnt]

It has been well known that the control arms for the Hotshot II and other models using the same parts are not really that durable. Tamiya could have made them thicker out of a different material like nylon, but instead they made them as light as possible using what I believe is polycarbonate. Well...if you have broken the rear control arms, then I have a DIY conversion that might work. No, it not some chinese metal control arm kit, we want something that still has some flexibility, like the rear control arms from a stock Traxxas Bandit. Yup! That's what we will use, stock Traxxas Bandit rear control arms, which you can find in almost any hobby store in the USA.

Just a disclaimer, use the proper safety devices and practices when using power tools and dealing with toxic materials. Doing this modification may cause some clearance issues between the original rear wheels and the pins, (fine for 2.2 buggy wheels). Shimming and additional grinding will be necessary for use with the original rear wheels.

Tools you will need:

A rotary tool, but keep speeds slow.

A drill(could be used instead of a rotary tool).

A 3mm or 1/8th inch drill bit.

A burr or course grinding stone bit.

A file or low grit sand paper.

Parts you will need:

Traxxas Bandit stock rear lower control arms.

2x M3×30 or 40mm screws.

2x M3 lock nuts.

Maybe some additional screws for the upper links.

TL01 rear knuckles/uprights or equivalent.

M3 spacers or washers(size will depend).

3mm rod ends, but length will depend.

3mm threaded rod or turnbuckle, but length will depend.

Ok, let's get started with the Traxxas Bandit rear control arms. This is what we need the power tools for. Using a burr or a grind disk/stone you need to remove a good part of the raised rib/boss where the shock mounting holes are, making it flat with the surface. This is necessary to keep the factory shocks in a close enough position to operate correctly but also not be too close to the motor on one side. Then when that is done pick the farthest outside hole (maybe 2nd most outside if you want) as the shock mounting hole and put in the shock end and lower spring retainer to see where and how much material needs to be removed to have the normal amount of movement for proper operation.

Just remove enough at the top and top corner to have just enough clearance, no more than that. Then with that done, use a file or sand paper to clean up the rough areas. 

Shortening the outer pins and removing extra material will be necessary for use with original wheels.

Next, the inside pin hole ends are just a little bit too close to fit. That's an easy fix, just file or grind the front inner screw pin ear/boss on the control arm until it just fits over the lower control arm boss on the transmission case on the car.

The the hard part is now done. Now if you noticed, the Bandit control arms are not the same length as the old control arms and the stock rear knuckles will not fit. More on that soon.

So to keep everything more than satisfactory using the original screw pins, put a drop of thin CA glue in the hinge pin holes of the new control arms just to coat the walls of the holes. Then once the glue has dried, drill the holes out trying with just one pass with a 3mm or 1/8th inch drill bit. The reasoning for this is because the pins Traxxas uses that are a little bit larger in diameter, so we want to fill the gap in a little bit for the Tamiya screw pins. Still trying to keep everything satisfactory because of the size difference from the original parts, use TL01 or equivalent rear knuckles/uprights along with some spacers to keep the knuckles centered enough when mounted in the control arm. Many things can be used as spacers, I used plastic washers and unused shock pistons lol.

Now the upper suspension links are needed. There are many choices for rod ends and turnbuckles, so I can't tell you the exact parts you want. Just make sure everything fits well enough and allow you to have -1 degree or so of camber. You can use threaded rod or fancy adjustable turnbuckles like I did, if it works, it works. Attach the upper ball end links to the rear of the upper control arm boss on the gear case using M3×30 or 40mm machine screws and locknuts.

With everything assembled make sure there are no issues. The lower shock ends should be able to use the original step spacers/bushings, which can be flipped around if needed. The rear wheels will be toed in a bit which may help with handling like on modern buggies. With this conversion done, the rear track width should still be within the ballpark of the original while still allowing plenty of room for the dog bone shafts to properly float without issues when the suspension goes through it's full motion of travel.

Just optional, but another thing that can be done is replacing the factory shock lower spring retainers to gain more clearance by the control arm.

Anyway, feel free to leave a comment if you have good ideas to add, just want to add a friendly  message, tried this yourself and want to show it off, or have any questions.