42391 TRF421X Steering Knuckle Arm - Tamiya 9803566  [9803566]

Replacement knuckle for TRF421X steering

Listed as Tamiya part number 9803566 and tied to reference 42391 TRF421X, this aluminium knuckle replaces the front steering pivot on hobby 1/10 scale touring cars built around the TRF421X layout.

It acts as the steering pivot that links steering inputs to the wheel hub and contributes to dynamic alignment changes such as camber gain and steering responsiveness. Replacing the knuckle arm is a routine procedure when correcting wear or experimenting with steering characteristics on a TRF421X chassis.

Installation follows common RC workshop practice: remove the wheel and hub carrier fastenings, unhook the steering linkage and any retaining pins, fit the replacement knuckle, then reassemble and torque fasteners to the vehicle maker's guidelines while securing clips or set screws. Confirm free hub spin and verify wheel alignment before running the model.

Setup note: a new knuckle can modify toe behaviour during suspension travel and the transient steering feel; introduce changes gradually and evaluate on short test runs. Also take the opportunity to inspect bearings, screws, and linkages for wear when changing this part.