FONZON 39/12T FULL METAL SPLIT FR/RR DIFF - ARRMA 8S SERIES FZCS83912T

Overview

The FONZON 39/12T Full Metal Split Front/Rear Differential for ARRMA 8S Series is engineered specifically for drivers who demand brute power and precision control on the roughest terrain. Whether you're a serious RC enthusiast running an ARRMA Kraton 8S, Outcast 8S, or EXB Series 8S model, or you're upgrading your existing RC car in the UK market, this differential represents a significant step up in drivetrain reliability and performance. Built to withstand the extreme torque and repeated impacts of large-scale bashing, the FONZON differential delivers smooth, consistent power delivery with exceptional long-term durability that will keep your RC car performing at its peak for years to come.

This is not a basic plastic differential – it's a fully CNC-machined component crafted from premium materials and designed for those who refuse to compromise on quality. The FONZON 39/12T arrives fully assembled and pre-filled with factory differential oil, meaning you can install it and get straight to the action without any complex setup or configuration. For anyone running a brushless RC truck or buggy on the 8S platform, upgrading to this metal differential is one of the most impactful modifications you can make to improve drivetrain performance, reduce noise, and extend the lifespan of your transmission system.

RC enthusiasts across the UK who bash hard, compete regularly, or simply want the best possible performance from their ARRMA 8S vehicle will appreciate the engineering excellence that goes into every detail of this component. The FONZON differential is ready to handle the demands of serious RC action, whether you're pushing the limits in off-road mayhem, competing in organised events, or enjoying weekend bashing sessions.

Key Features

• CNC-Machined 4340 Nickel-Chromium Alloy Steel Gears — Every gear is precisely machined from 4340 nickel-chromium alloy steel, which provides maximum strength and durability under extreme torque conditions. This material choice ensures that your differential can handle the punishment of high-powered 8S brushless systems without risk of gear stripping or damage, giving you peace of mind during intense driving sessions.
• Helical Gear Design for Smooth, Quiet Operation — The helical gear profile used in this differential provides much smoother engagement compared to standard spur gears, resulting in quieter operation under load and reduced noise pollution. This also means less vibration transferred to your chassis, which translates to better handling and more predictable vehicle behaviour during high-speed runs and aggressive manoeuvres.
• Rigid 7075-T6 Aluminium Alloy Diff Case — The centre housing is crafted from premium 7075-T6 aluminium alloy, one of the strongest aluminium variants available in RC applications. This material provides superior rigidity to keep all internal components perfectly aligned during extreme driving conditions, whilst also keeping overall weight down compared to heavier steel alternatives, helping to maintain optimal weight distribution and handling characteristics.
• Grade 12.9 Corrosion-Resistant Screws — High-quality grade 12.9 fasteners ensure long-lasting assembly integrity and resist corrosion, which is particularly important for UK drivers who may encounter wet conditions or salt-treated roads. These premium screws maintain their tension over hundreds of drive cycles, preventing the differential case from coming loose or developing play in the drivetrain.
• High-Quality Matched Drive Cup Bearings — Precision-matched drive cup bearings provide stable, efficient rotation and ensure that torque is transmitted smoothly through the drivetrain with minimal friction and play. These bearings are selected and matched as a set to work together perfectly, eliminating the performance variations that can occur with mismatched bearing sets used in budget differentials.
• Factory Pre-Filled with 100K cSt Differential Oil — The differential arrives completely pre-filled with premium 100K cSt differential oil, which is the correct viscosity for optimal performance in 8S applications. This eliminates the guesswork and mess associated with filling differentials yourself, and ensures you're using the exact fluid specification recommended by the manufacturer for peak performance.
• Fully Assembled and Ready to Install — Unlike many aftermarket differentials that require assembly and adjustment before use, the FONZON arrives completely assembled and ready for immediate drop-in installation. Simply remove your original differential and swap this unit in place – no additional setup, adjustment, or tuning required, meaning you can be back out driving within minutes.

Technical Performance

The FONZON 39/12T represents the pinnacle of differential engineering for the ARRMA 8S platform, incorporating design principles and materials that were previously reserved for competition-grade RC vehicles. Every component has been carefully selected and engineered to deliver measurable improvements in performance and longevity. The 4340 nickel-chromium alloy steel used for the gears is one of the toughest materials available in modern RC manufacturing, offering both hardness and toughness – a combination that prevents gears from either snapping under shock load or gradually stripping under sustained high torque. The 39/12T gear ratio has been specifically designed for the 8S platform, providing optimal power delivery and acceleration characteristics across a wide range of driving conditions.

The helical gear design deserves special mention, as this engineering choice has profound implications for real-world performance. Unlike traditional spur gears that engage along a single line of contact, helical gears engage gradually across their faces, distributing load more evenly and smoothly. This results in a reduction of the gear rattle and whine that many drivers find objectionable in standard differentials, and more importantly, it significantly reduces stress spikes on individual gear teeth, which extends the service life of the differential considerably. The 7075-T6 aluminium case is not just strong – it's engineered to maintain perfect dimensional stability even under repeated impacts and extreme temperature changes. This level of rigidity is critical because any flex in the differential case causes the internal gears to misalign, increasing friction, heat generation, and wear rates. By maintaining perfect alignment, the FONZON differential operates with minimal heat generation and maximum efficiency, which means more of your battery's energy goes into powering your vehicle rather than being wasted as heat.

For UK RC enthusiasts running brushless 8S systems – whether that's a Hobbywing, Spektrum, or other high-performance ESC – this differential is the perfect match. It's been engineered to handle the kind of sustained high-torque output that modern brushless motors deliver, making it an ideal upgrade for anyone who's experienced differential failure or inconsistent performance with standard differentials. The pre-filled differential oil means you're getting the exact fluid viscosity that the engineers at FONZON determined was optimal for this application, ensuring perfect damping characteristics across the full range of driving temperatures you'll encounter in the UK.

What's in the Box

• FONZON 39/12T Full Metal Split Front/Rear Differential for ARRMA 8S
• Fully assembled differential unit
• Pre-filled with 100K cSt differential oil
• Ready for immediate installation

Frequently Asked Questions

• Is the FONZON 39/12T suitable for my ARRMA 8S RC truck? — Yes, this differential is specifically engineered as a direct fit for all ARRMA 8S platform models, including the Kraton 8S, Outcast 8S, and EXB Series 8S models. It represents a significant upgrade from the standard differentials supplied with these vehicles and is compatible with both front and rear differential positions, making it a versatile upgrade option for your setup.
• What improvements will I see when I upgrade to this metal differential? — You'll immediately notice quieter, smoother operation compared to standard plastic differentials, with noticeably less gear rattle and whine. More importantly, you'll experience improved reliability and consistent performance over extended use, with significantly reduced risk of differential failure even under extreme driving conditions. The smoother power delivery also translates to better traction and more predictable handling characteristics, particularly during hard acceleration and cornering.
• Is this differential better than other aftermarket options available in the UK? — The FONZON 39/12T uses premium materials – 4340 nickel-chromium alloy steel for the gears and 7075-T6 aluminium for the case – which represent the highest standard in RC differential engineering. The CNC-machined construction ensures tolerances far tighter than most competing products, and the helical gear design provides smoother, quieter operation. Combined with the factory pre-fill and complete assembly, it offers exceptional value compared to alternative upgrades on the UK RC market.
• Do I need any special tools to install this differential? — No, the FONZON differential is designed for straightforward drop-in installation. As long as you have basic RC tools (screwdrivers, Allen keys) and are familiar with removing your vehicle's original differential, installation should take just a few minutes. No special alignment tools, shims, or adjustment procedures are required – it's designed to bolt straight in and work perfectly.
• Will this differential work with my brushless 8S setup? — Absolutely. This differential has been specifically engineered for modern high-torque brushless systems on the 8S platform. Whether you're running a Hobbywing, Spektrum, or other premium ESC, the FONZON differential is built to handle the sustained high-torque output that these systems deliver. It's an ideal pairing for any serious brushless 8S setup.
• How long will this differential last? — The premium materials and precision engineering mean this differential will provide years of reliable service even under heavy use. The matched drive cup bearings, helical gear design, and rigid case construction all work together to minimise wear and extend service life significantly compared to standard differentials. Most users report that properly maintained FONZON differentials show negligible wear even after hundreds of operating hours.
• Is the differential oil that's pre-filled the correct specification for my vehicle? — Yes, the 100K cSt differential oil used in the factory fill is specifically selected for optimal performance in 8S applications. This viscosity provides the perfect balance between smooth operation and proper torque transmission across the full range of driving temperatures you'll encounter in the UK climate.

Why Buy from RC Model Shop?

RC Model Shop is a trusted UK RC retailer and authorised dealer for all the brands we stock, including Traxxas, ARRMA, Losi, FTX, Hobbywing, Spektrum and more. Based in Walsall, we have a physical store where customers are welcome to come in, view products and purchase in store. Whether you are a seasoned competitor, a weekend basher, or just discovering the world of RC for the first time, our team of experienced RC enthusiasts is here to help you find the perfect setup and provide ongoing support. Order the FONZON 39/12T FULL METAL SPLIT FR/RR DIFF - ARRMA 8S SERIES FZCS83912T today with confidence, knowing you are buying from an authorised retailer with genuine products, expert knowledge and a commitment to customer satisfaction. Shop online or visit us in Walsall — we look forward to helping you get the most out of your RC experience.