If you own a Traxxas TRX-4, you already know it's one of the best scale crawlers on the market. Portal axles, locking differentials, high/low transfer case — the platform is excellent. But out of the box it's set up as a showroom-friendly demo truck. Serious crawling on Australian terrain — rocky creek beds, sandstone ledges, steep red dirt trails — demands more traction, better weight distribution, and parts that don't strip on the third rock section. That's where brass comes in.
Why Brass Matters for Crawling
Traction in crawling comes from wheel pressure — specifically how evenly and consistently each tyre presses against the surface. The lower and more forward your centre of gravity, the more weight sits over the front axle, which is typically the driven axle doing the climbing work.
Brass is roughly 8.5 g/cm3 — more than twice the density of aluminium (2.7 g/cm3) and about seven times denser than most RC-grade plastics. When you replace plastic or aluminium parts with brass equivalents, you add meaningful weight exactly where crawling physics demands it: at axle level and at the front of the truck. That weight presses the tyres into the terrain. More tyre contact under load equals more traction. It's simple physics and it works.
The secondary benefit is durability. Brass doesn't crack on impact the way plastic does, and the added mass tends to mean parts are machined thicker, giving better thread engagement and longer service life.
The Essential Brass Upgrades (Start Here)
Two parts give you the biggest traction improvement per dollar on a TRX-4. Start here before anything else.
Brass Portal Cover Set
The TRX-4 uses portal axles — a design where the final drive gear is at the wheel hub rather than the axle centre. This gives excellent ground clearance and the signature TRX-4 look, but it also means there's a large cover on each portal that is, by default, made of plastic. GPM Racing's brass portal cover set replaces all four covers with machined brass equivalents. This single upgrade adds roughly 300–400g at the lowest point of the axles — exactly where you want it. It's the single best first upgrade for TRX-4 crawling performance. Bolt-on, no modification required.
Brass Front Axle Weights
Purpose-built brass axle weights bolt directly to the front axle housing and add focused mass at the front of the truck. Combined with brass portal covers, the front axle becomes significantly heavier — translating directly into front tyre pressure on climbs. These are simple, flat bolt-on pieces with no moving parts or complexity. Easy first upgrade.
Steering Assembly Brass Upgrades
Once you have the portal covers and axle weights sorted, the steering assembly is the next priority.
Brass Steering Knuckles and C-Hubs
Brass steering knuckles serve a dual purpose: they add weight at the front wheel (improving traction further) and they're significantly more durable than stock plastic. The knuckles take direct impact on ledge strikes and rock hits — brass holds up where plastic chips and cracks. The C-hubs (also available in brass from GPM) maintain consistent front geometry under load.
The weight placement benefit here is excellent. Brass knuckles are at the outermost point of the front axle — the furthest from centre — which has a greater moment-arm effect on front traction. In practice, you'll notice the front tyres biting harder on technical climbs.
The Full Brass Build — Front End
To complete the front-end brass package, add the front bumper and servo mount in brass.
Brass Front Bumper and Servo Mount
The brass front bumper adds weight at the very front of the truck — good for nose-down weight on climbs — and protects the front end from rock strikes better than plastic. The brass servo mount keeps your steering servo positioned rigidly, which matters in technical terrain where wheel flick and resistance through the linkages can move a plastic mount.
Together, the full brass front-end package (portal covers, axle weights, knuckles, bumper, servo mount) typically adds 500–700g concentrated at the front and at axle level. On a TRX-4 that weighs around 3.5kg stock, this is a meaningful and immediately noticeable change.
Aluminium Upgrades That Complement Brass
Not everything needs to be brass. Aluminium excels for structural parts where weight is less critical but rigidity and durability are.
- Upper and lower link set: Aluminium links maintain suspension geometry consistently. Stock plastic links flex under articulation, changing your geometry mid-crawl. Aluminium holds true.
- Aluminium shock towers: Rigid mounting points for your shocks, ensuring consistent damping and geometry at full articulation.
- Low battery tray: Moves the battery pack as low as possible in the chassis, lowering the centre of gravity significantly. One of the most impactful CG upgrades available.
- Chassis skid plate: Protects the underside electronics and battery on rock drags. Australian rocky terrain is hard on exposed components.
- CVD drive shafts: Steel CVD shafts replace the stock cup-and-dog bone design. They handle the full articulation range of TRX-4 without binding or popping out, which is a genuine stock weakness on extreme angles.
How Much Does a Full TRX-4 Brass Build Cost?
A complete brass and aluminium build on a TRX-4 typically costs $400–$600 AUD depending on brand choices and which aluminium parts you include. Broken down by stage:
- Stage 1 (portal covers + axle weights): ~$90–120
- Stage 2 (knuckles + bumper): ~$80–120
- Stage 3 (aluminium links + towers + battery tray): ~$150–200
- CVD drive shafts: ~$60–80
Total weight added in a full build: typically 500–800g depending on specification. The truck crawls noticeably better from Stage 1 onwards — you don't need to complete the full build before seeing results.
Building in Stages — Recommended Order
You don't need to do everything at once. This order gives you the best traction improvement per dollar at each stage:
- Stage 1: Brass portal covers + brass axle weights. Biggest traction improvement, lowest complexity.
- Stage 2: Brass steering knuckles + brass front bumper. Complete the front-end weight package.
- Stage 3: Aluminium suspension links + shock towers + low battery tray. Lock in your geometry and lower the CG.
- Stage 4: CVD drive shafts + chassis skid plate. Drivetrain reliability and rock protection.
After Stage 2, your TRX-4 will be a noticeably better crawler. After Stage 3, it'll be capable of terrain that would have stopped it completely in stock form. The full build is excellent.
The Bottom Line
Brass upgrades are the single most effective modification for TRX-4 crawling performance. The physics is simple, the installation is bolt-on, and the results are immediately apparent. Start with portal covers and axle weights, add knuckles and bumper, then complete with aluminium links and suspension components.
Browse the full TRX-4 upgrade range: Traxxas TRX-4 Parts