Tamiya 3451581 Upper Arm Mount B for TRF421X 42391 TRF421 hop-up part  [3451581]

Upper Arm Mount B for TRF421X

This is the replacement Upper Arm Mount B identified by part number 3451581 and linked to code 42391 for the TRF421X chassis. The component is offered as an RC-scale spare designed to restore or alter the upper arm mounting point without modifying the surrounding suspension or arm assemblies.

Functionally the mount locates the upper arm relative to the shock tower and suspension mounting plate, so it plays a direct role in ride height, camber roll center, and track stability when used as part of setup changes. Use it to replace a damaged mount or to maintain correct geometry after routine maintenance.

Installation is straightforward for hobbyists with basic tools: remove the affected mount using the original hex screws, position the new mount to match factory orientation, and secure with the same fasteners. Verify arm travel and suspension binding before running, and re-check wheel alignment after the first test run.

This part is an OEM-format spare intended for TRF421X owners who need a like-for-like replacement for part 42391 or who are managing chassis geometry during tuning sessions.