How to Build the TRX-4 Sport Kit: Part 2

We Start with the TRX-4's Revolutionary Portal Axles and Locking Differentials

It's time to start building our TRX-4 Sport kit. If you missed Part 1, click here to go back for a look at the TRX-4 Sport kit we’ll be assembling, and what you’ll need to complete yours. We’re not going to show every screw going in, but we will highlight some tips for the build and show you the major components. If you’d like to follow along with the manual, you can view it as a PDF here.

There's no better place to unwind than the RC bench.

Assembly begins with the transmission. As the manual points out, make sure to seat the bearings fully into their recesses. If there isn’t room to get your thumb in over the bearing for a good squeeze, you can use the 4-way wrench to press the bearing down into position. Inserting cross pins can be tricky. A small set of needle-nose pliers will make the job much easier.

Press bearings into position

Use the 4-way wrench

Use needle-nose pliers

Resist the temptation to slather on a ton of grease, which will just make a mess inside the gearbox. All you need is a spot on each gear. As the gears turn, they’ll distribute the grease.

Greasing the transmission

A little grease goes a long way

Be sure to tighten the slipper clutch as detailed in the manual, so the spring washers are flat. If you prefer to build your TRX-4 without a slipper clutch, you can get the 8249 Slipper Eliminator plate set.

Tightening the clutch

Compress the washers fully

Here is the completed transmission. The manual made the assembly easy!

We've reached the axle assembly portion of the manual. The included locked spools are perfect for hard-core climbing when you need maximum traction. We're going to install the optional 8195 T-Lock differential set in our trail rig. The T-Lock differentials provide the same level of traction when you need it, but also disengage for increased maneuverability. Just flip the toggle switch on top of the transmitter to engage them. The kit includes the front and rear shift servos, locking differentials, and all the bits required to install them as well as instructions.

8195 T-Lock Differential Set

The kit includes everything you need

Insert the crosspin into the differential output, then install the locking slider over it so its teeth engage with the recesses in the differential housing. The locking slider is keyed to fit over the crosspin.

Align the slider and crosspin

Completed differential

T-Lock differential action

When assembling the portals, install the input gear so it is captured by the 10 x 15mm bearing. The gear should sit flush with the back of the portal housing and the bearing face.

Installing the input gear into the portal axle

Make sure the input gear is flush

Here is a completed rear axle

With the rear axle complete, it's time to tackle the front. This would be a good time to double-check that you installed the correct T-Lock cable in the rear. The longer of the two cables goes to the rear so you should have the shorter cable left for the front. The front axle assembles just like the rear with the addition of the caster blocks to steer the portal assemblies. The blocks are labeled L and R to indicate left and right, but they will still fit if installed backwards. Before you tighten everything up, make sure they are installed correctly. When properly installed, the caster blocks “lean back” to provide the correct caster angle for the steering system.

Installing the caster blocks

The top of the caster block should "lean back"

When assembling the front driveshafts, install the CV crosspin into the shaft first. Next, install the input gear over the shaft and secure it with the the thin crosspin. The 12 x 18 mm bearing captures the pin so it can’t fall out.

Front axle assembly

Crosspin installation

Completed input gear

With the front portal axles complete, all you need to do is install them into the axle assembly and secure them with screws. The portal with the short driveshaft goes on the left side of the axle.

Completed portal axles

Completed axles and transmission

That's all for part 2 of our TRX-4 Kit build. Coming Up in Part 3: the chassis! Missed a step? Click here to go back to Part 1.

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