Ultimate Hoss 4X4 VXL Build: Part 1

Aluminum Torque-Biasing Center Drive Unit Housing
The Hoss comes with a Torque-Biasing Center Drive as standard equipment, constructed with a steel spur gear and composite housing. The Center Drive is a sealed differential with four spider gears for strength, but unlike standard differentials with thinner silicone fluid, the Center Drive is packed with near-solid silicone. The thicker silicone provides a limited-slip effect to resist “diffing out,” which causes the front tires to balloon. We're swapping the composite housing for 6781 cast aluminum version because it's stronger and better dissipates heat. If you run your Hoss hard on 3-cell power through multiple battery packs, the aluminum-housing upgrade will put more hours between silicone changes and keep the Torque-Biasing Center Drive performing its best.

The Center Drive includes fresh seals and bushings that fit between the housing and spider gears, so the gears don’t wear into the housing. You can scoop the thick silicone out of the Center Drive and transfer it to the aluminum housing, but it’s easier to just get a fresh tub of 1M weight silicone. That’s M as in million; diff-oil weights are usually in the 50,000 – 100,000 weight range, so that gives you a hint just how thick this goop is.

If digging into the Center Drive sounds like more wrenching than you want to get into, you can just swap out the entire unit. The complete 6780 Torque-Biasing Center Drive comes with the aluminum housing and includes a steel spur gear and splined driveshaft input. This is a great way to go if you’ve also got a Rustler 4X4, Slash 4X4, or Stampede 4X4 and you’d like to replace its slipper clutch with a torque-biasing differential. Install the aluminum-housing Center Drive in your Hoss, and transplant the Hoss’s composite-housing Center Drive unit into your other 4X4 model.

Spiral-Cut Machined Ring & Pinion Gears
The Hoss gets steel ring and pinion gears as standard equipment, designed for extended wear with 3-cell LiPo power. Should you ever wear them out, or simply want to build the most bomb-proof Hoss possible, there are ever stronger spiral-cut gears available. The optional spiral-cut ring and pinion gears are CNC-machined from a solid block of steel. The teeth are shaped differently too, with a slight curve or “spiral cut” instead of being straight. This shape minimizes backlash between the gears and maximizes tooth traction, making them ideal for high-torque, high-speed applications—like the Hoss. Spiral-cut gear teeth also wear longer than straight-cut teeth, so the optional machined-steel gears may be the last your Hoss ever needs.

The ring and pinion gears are sold in front and rear sets

Spiral-cut gears provide a larger contact patch

A sliced pool noodle makes a good stand

Before installing the Torque-Biasing Center Drive and rear module, we traded the blue center shaft for an orange one. You can also get the shaft in red and green.

Steel-Spline CV Driveshafts
The Hoss already has Traxxas’ strongest 1/10 scale composite telescoping universal-joint driveshafts, but there's an even stronger option part available. Traxxas’ steel constant-velocity shafts use bell-style joints instead of yoke-style universal joints for maximum efficiency and greater deflection angle without binding. The male and female shaft-halves are deeply splined to transmit high torque. This allows the shaft to telescope with a CV joint firmly attached at both the gearbox and wheel.

Steel driveshafts are thinner, but stronger

Precision-machined parts provide smooth power delivery

Aluminum hubs for extra strength

Machined 4 mm Motor Plate
To provide extra support for the 540XL motor and extra heat-sink effect, we traded the stock 3 mm motor plate for the optional 4 mm version. In addition to the extra stiffness of the thicker material, the option plate’s machined-in reliefs create more surface area to dissipate heat. It’s also a trick-looking part, but the extra machining is hidden once installed.

The 4 mm machined motor plate (left) provides extra cooling and looks great

You'll need to file the fixed gear adapter slightly to fit the new motor plate

That ends part 1 of our ultimate Hoss build. Now that we've upgraded the drivetrain, we'll move on to the suspension and steering. Be sure to check out the full line of Hoss accessories and come back next week for Part 2