Blue aluminum upgrade parts| |
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View the Full Line of TRX-4 Accessories
Benefits of Portal Axles
Before the screws start flying, let us pause to appreciate the beauty of the TRX4’s portal axle design. The gear reductions on the end of the axle allow the T-Lock™ differential to sit much higher than a normal axle’s differential, which greatly increases the TRX-4’s ability to straddle obstacles. The axle silhouette in red shows how much lower a regular straight axle would be. Extra ground clearance is just half of the portal design’s benefit; because of the axle’s very low (numerically high) total gear reduction, the driveshafts that link the axles to the transmission spin at higher RPM for any given speed compared to a standard solid axle. Higher driveshaft RPM means less torque is transferred to the axle, so torque-twist is reduced to near zero.
Clearance with portal axles
Clearance without portal axlesFront Axle Removal & Disassembly
We’re focusing on the front axle since it’s slightly more complex than the rear axle. After putting the front axle together, you’ll cruise right through the rear axle. Remove the T-lock shift cable by twisting the ball cup off the servo, then loosening the screw that holds the cable. You can leave the screw in place in the part, so you won’t have to look for it later. To free the axle, remove the screws that pass through the shocks and lower links, the steering link where it connects to the servo, and the Panhard bar where it connects to the chassis. Just follow the arrows. Once the axle is out, remove the screw pin that holds the driveshaft in place, and remove the shaft.
Remove the T-Lock shift cable
Disconnect and remove the shift cable from the servo.
Remove the axle
Remove all the screws securing the axle to the truck to release the axle.
Disconnect the driveshaft
Remove the screw pin to separate the center driveshaft from the axle.
Next, remove the portal assemblies by taking out the kingpins (these are the screws the portals pivot on to provide steering action). Place the axle on its side as shown, so it’s easier to grab the bushing that the kingpin screw passes through. You’ll need those bushings later. With the kingpins and portal assemblies removed, the three screws that hold the caster block are revealed. Remove the screws and the caster blocks.
Remove the kingpins
Remove the portal assemblies and caster blocksDifferential Ring & Pinion Install
We need to take the diff cover off to install the machined steel ring and pinion gears. The screws pass through the back of the axle. Remove all four screws, then pull the cover straight away from the axle to reveal the T-Lock differential. Push and pull the T-Lock cable so you can see how the shift fork (the C-shaped plastic part that pivots) moves the drive dog (the toothed part) in and out to lock and unlock the diff. Pretty cool, and surprisingly simple. Seeing and understanding how a mechanism operates always makes it easier to work on.
Remove the differential cover screws
Remove the differential cover
Remove the T-Lock assemblyGently pull the shift fork back until it’s free of the axle (just a few millimeters is all you need), then walk the fork off of the shift cable. Now you can pull the differential out. With the differential out, the pinion can now be removed. Push on its shaft where it exits the axle housing, then grab it from inside the axle. Remove the bearing that fits onto the ring gear, and remove the four screws that secure the gear. Remove the ring gear from the diff housing and take out the output gear that fits into it.
Remove the pinion gear
Take the ring gear off
Remove the output gear
Compare the ring and pinion gearsMachined Ring and Pinion Gears
Here’s the machined steel ring and pinion next to the stock parts. The stock parts are made in a mold using heat-treated steel and plenty strong, but the machined versions are even stronger. We’re installing part 8279R, which duplicates the stock 11/34 (3.09:1) ratio. You can also get the gears as 8288 with a 10/35 (3.5:1) underdrive ratio, or as 8287 with a 12/33 (2.75:1) overdrive ratio. Just reverse the disassembly steps to install the new ring and pinion and reinstall the differential.
Note: Whether full-scale or RC, most 4WD vehicles have identical gear ratios for the front and rear axles, so all four wheels run at the same speed. In a road car, doing anything else would greatly increase strain on the drivetrain parts and accelerate tire wear. But for off-road vehicles, where the tires have some slip, slightly different axle ratios can improve climbing and crawling performance. If you are only installing the machined ring and pinion gears, you may do so without removing the axle from the truck. We're going all-in on this build so it made more sense to change them with the axles out.
Aluminum Portal Parts Install
Work on one portal assembly at a time, so you can refer back to a factory-built unit as you wrench. Remove the three screws that capture the shaft bearing, and pull the shaft straight back. Then remove the two screws in the front of the portal, and six remaining screws on the bearing side.
Remove the portal screws
Remove the shaftWith all the screws out, you can open up the portal housing and take out the output gear and stub axle. Remove the screw pin that holds the drive hex in place to free the gear and stub axle.
Remove the output gear
Remove the crosspinThe TRX-4’s stock steel shafts are built to last, but the machined chromoly versions peg the tough-stuff needle—a good upgrade if you’re installing a higher-output power system. The stock and upgrade shafts both use efficient CV-style universal joints. The machined steel install like the stock versions, just reverse the disassembly steps.
Machined chromoly driveshaftsAdding Blue-Anodized Aluminum Accessories
Instead of reinstalling the stock plastic parts, we’re swapping them for machined aluminum versions. In addition to the killer cobalt blue shown here, you can get the parts in red, green and gray. You’ll note these parts include screws with a patch of blue thread-lock pre-applied for you, since thread-lock should always be used in parts that thread into metal. Save the non-thread-locked screws from the plastic parts for your spares box.
Blue anodized-aluminum partsReverse the axle disassembly steps to build the aluminum portal housings. Pay attention to the caster block orientation; the longer leg goes on the bottom, and kicks toward the front of the truck. Be sure to remove all the bearings from the plastic parts and press them into the aluminum versions. It’s easy to miss the 4X10 mm bearing that goes in the top of the outer portal housing. To remove the bearings from the plastic parts, insert whichever part goes into the bearing, then gently rock it side to side and “walk” the bearing out. When pressing the bearings into the aluminum parts, be careful to slide them straight in and make sure they’re fully seated. A firm finger press should be all it takes.
C-hub orientation
Bearings insertedIf you work on one half of the axle at a time, you can refer back to the assembled portal if you need help remembering how the parts fit together. You can also look up the Exploded Views at Traxxas.com. Just find your model and click the Support tab.
Completed portal axle
Exploded ViewNow that’s a sweet-lookin’ axle! Bonus: the aluminum parts are 2.5 ounces heavier than the plastics they replace, which will help our Ultimate TRX-4 find even more traction on the trail. If you want to really pile on the ounces, you can install the optional portal weights 8267. These will increase weight by 34 grams each for extra stability and a lower center of gravity.
Completed axleALUMINUM MOTOR PLATE INSTALL
Swapping out the motor plate is very easy on the TRX-4. Start by removing the gear cover—just take out the two screws that hold it in place. The cover captures the motor plate, so you now you can just lift the motor and plate out. Note that the holes are lettered, and the “C” pair of holes is used for the 11-tooth pinion. The aluminum part is lettered just like the stock version. It’s too bad you can’t see that nice blue anodizing once it’s installed, but you do get the benefit of reduced flex and increased heat dissipation.
Remove the gear cover
Motor plate detail
Aluminum motor plateSee Part 1: custom Defender body, beadlock 1.9″ tires and wheels, and LED lighting.
We’re Not Done Yet. Jump to part 3 for suspension upgrades and servo swap!
Get your wrench on, and show us how your Trail Truck build turned out! Post your pics to Facebook, Instagram or Twitter with #MyTRX4Build, and we’ll be sure to share some of our favorites.
