Overview
The ARRMA Open F/R Diff Set GP4 5mm 10K is a factory-assembled differential unit designed for competitive and recreational RC car enthusiasts across the UK. This pre-assembled component is ready for immediate installation, making it an ideal upgrade or replacement part for ARRMA 1/8 scale vehicles. Whether you're maintaining your existing RC monster truck or fine-tuning your setup for optimal performance, this open differential provides the precise mechanical advantage needed for consistent handling and predictable on-track behaviour. As a trusted supplier of RC car spares and tune-up options, we stock this component because it represents genuine ARRMA engineering backed by years of development in 1/8 scale RC racing.
The open differential is a fundamental transmission component that distributes engine power equally between the front or rear axles, making it the preferred choice for rear-axle applications in competitive RC car racing. This particular unit comes pre-filled with 10,000 cSt silicone oil, which means you can install it straight from the box without additional preparation or servicing. For RC enthusiasts looking to upgrade their drivetrain or replace worn components, this factory-assembled solution eliminates guesswork and ensures compatibility with your ARRMA vehicle. The GP4 43T spiral cut main gear provides enhanced durability under the extreme loads and high-speed cornering forces common in competitive RC bashing and racing scenarios.
This differential set is compatible with several ARRMA platforms including the 1/8 KRATON 6S EXB 4X4 RTR Speed Monster Truck and the MOJAVE 6S V2 BLX models, making it a versatile choice for owners of these popular RC vehicles in the UK RC car market.
Key Features
- Factory Assembled and Pre-filled — This differential arrives completely assembled and filled with 10,000 cSt silicone oil, eliminating the need for time-consuming manual assembly and preparation, so you can install it immediately and get back to driving your RC car without delay.
- Tough Steel Internal Gears — The internal gear construction uses high-quality steel that maintains durability through extended use in all weather and terrain conditions, resisting wear and delivering consistent performance across multiple racing seasons.
- Traditional Open Differential Assembly — The open differential design provides equal power distribution to both wheels on the same axle, which is the industry-standard configuration preferred by competitive RC drivers for predictable handling and balanced cornering on both left and right turns.
- Strong Composite Diff Case with Integrated Steel Insert — The composite case material balances weight savings with structural integrity, whilst the integrated steel insert reinforces the assembly against impact damage and ensures longevity under demanding use.
- GP4 43T Spiral Cut Steel Main Gear — This larger-diameter, spiral-cut main gear provides increased contact surface area and load distribution compared to standard straight-cut gears, resulting in improved durability when accelerating hard and maintaining speed through high-load corners.
- Metal Cross Shafts for Enhanced Efficiency — Metal cross shafts replace polymer alternatives with superior strength and consistency, reducing flex during power transfer and maintaining precise differential action even when driving hard through technical courses.
- Rubber Shielded Bearings — Sealed rubber shields protect the internal bearings from dust, dirt, and moisture whilst still allowing smooth rotation, ensuring fast and efficient operation during both indoor and outdoor RC driving sessions.
- Optimised for Rear Axle Application — The open differential design is specifically favoured on rear axles where equal power distribution improves traction stability and prevents inside-wheel slip during cornering, delivering more predictable and controllable handling characteristics.
Technical Performance
This ARRMA differential represents professional-grade transmission engineering designed to meet the demands of competitive 1/8 scale RC car racing. The 43T GP4 spiral cut main gear is the cornerstone of the assembly, providing a larger effective diameter than smaller gear options and distributing rotational loads across a wider contact surface. Spiral cut gearing produces smoother meshing action compared to traditional straight-cut designs, reducing gear noise and minimising vibration transmission through the chassis during high-speed running. The 10,000 cSt silicone oil fill provides the correct viscosity for balanced differential action—thick enough to prevent excessive slip during cornering but fluid enough to allow quick response when transitioning between acceleration and braking. The composite differential case with integrated steel insert is engineered to withstand the lateral forces generated during aggressive cornering at racing speeds whilst remaining lightweight enough to minimise unsprung mass. Metal cross shafts eliminate the flex found in polymer alternatives, ensuring that power is transferred consistently to the wheels without losses caused by component deflection. The rubber-shielded bearings provide robust sealing against contamination whilst maintaining the smooth, low-friction rotation essential for reliable differential function across multiple runs and racing heats. This is a genuine ARRMA component designed to work seamlessly with compatible vehicles including the KRATON 6S EXB and MOJAVE 6S V2 BLX models, both highly popular choices for serious RC car enthusiasts across the UK.
What's in the Box
- 1 x Factory Assembled Open Front or Rear Diff
- GP4 43T Spiral Cut Gear
- 10,000 cSt Silicone Oil (pre-filled)
What You Need to Complete
- ARA310979 - Main Input Gear 10T Spiral Cut GP4 5mm (required to complete the differential assembly)
Frequently Asked Questions
- Is the ARRMA Open F/R Diff Set GP4 5mm 10K suitable for beginners? — This is a component designed primarily for experienced RC car drivers who understand transmission maintenance and tuning. It is not an item for complete beginners but rather an upgrade or replacement part for those already familiar with maintaining RC vehicles. If you are new to RC cars, we recommend starting with a ready-to-run vehicle and learning basic operation before upgrading components like differentials.
- What does the 10K cSt silicone oil specification mean? — The 10,000 cSt (centistoke) rating describes the viscosity or thickness of the silicone oil. Thicker oils (higher numbers) create more resistance to slipping but slower response, whilst thinner oils allow quicker differential action but more slip. The 10K rating is the standard specification from ARRMA for this differential, providing the ideal balance for competitive racing across various track conditions.
- Which ARRMA vehicles are compatible with this differential set? — According to the specification, this differential is compatible with the ARRMA 1/8 KRATON 6S EXB 4X4 RTR Speed Monster Truck and the ARRMA MOJAVE 6S V2 BLX models in both red/black and green/black colour options. These are both 1/8 scale off-road racing vehicles popular among UK RC car enthusiasts.
- What is the difference between an open differential and a limited-slip differential? — An open differential, like this unit, distributes power equally between both wheels on an axle, allowing them to rotate at different speeds during cornering. A limited-slip differential restricts the speed difference between wheels, improving traction in slippery conditions but offering less inside-wheel freedom during sustained turns. The open differential is preferred for rear axles in racing because it provides predictable handling and reduces undesirable inside-wheel slip during cornering manoeuvres.
- Do I need any tools to install this differential? — Installation will require standard RC car maintenance tools and mechanical knowledge of differential assembly. Because this unit arrives pre-assembled and pre-filled with silicone oil, you are not required to perform internal assembly, but you will need to remove the old differential and install this one correctly. We recommend consulting your vehicle's manual or seeking assistance from experienced RC car builders if you are unfamiliar with this procedure.
- What other components do I need to complete the differential system? — You will need the ARA310979 Main Input Gear (10T Spiral Cut GP4 5mm) to complete the assembly. This input gear meshes with the 43T main gear included in this set to transfer rotational force from the drivetrain to the differential.
- Is this differential suitable for high-speed off-road racing? — Yes, absolutely. The steel internal gears, composite case with steel insert, and spiral cut main gear are all engineered to withstand the demands of high-speed 1/8 scale RC car racing. The open differential configuration is specifically preferred for rear axles in racing situations because it delivers predictable and controlled handling during aggressive cornering and acceleration sequences.
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 ARRMA Open F R Diff Set GP4 5mm 10K 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.
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