Tamiya TRF421X Upper Arm Mount B 3451581 replacement 42391  [3451581]

Mount Function and Setup Notes

This replacement Upper Arm Mount B is listed under part number 3451581 and is associated with code 42391 for the TRF421X chassis. It is intended as a spare to restore or modify the upper arm mounting location while leaving the rest of the suspension and arm assemblies unchanged.

The mount defines the upper arm position relative to the shock tower and suspension mounting plate, so it has a direct impact on ride height, camber roll center, and tracking during setup changes. Install it to replace a damaged mount or to maintain proper geometry after service.

Installation requires basic tools: remove the old mount with the original hex screws, place the new mount in the same factory orientation, and secure using the original fasteners. Inspect for binding, confirm arm travel, and perform a short shakedown run to ensure alignment is correct.

This unit is a like-for-like spare for TRF421X owners who need a direct replacement for part 42391 or who are adjusting chassis geometry in tuning sessions.