TRX-4 Rear Aluminium Gearbox Mounts and Knuckles, TRX4H100R by GPM  [TRX4H100R]

Rear gearbox and knuckle replacement for TRX-4 crawlers

This 54-piece aluminium upgrade set is intended as an aftermarket replacement for TRX-4 trail crawlers, focussed on the rear gearbox housing and knuckle arm assembly. The package replaces rear box mounts, both inner and outer knuckles, rear axle joint and shaft, spindle gears and supplies stainless fasteners to preserve stock interfaces while changing some mount positions.

How it fits and what it does: the parts secure the gearbox to the knuckle arms, improve internal gear alignment and relocate the lower shock mount to enable adjustments to damper height and angle. Adjustments are made by fitting the shock lower eyelet into alternate holes provided on the knuckle and mount plates.

Construction notes: primary pieces are formed from 6061 T6 aluminium with an open knuckle design to simplify assembly. After installation the shock bodies sit slightly more outboard than stock which helps chassis stability and allows a small rise in ride height. Knuckle internals have larger pitch and diameter gears plus a lower axle centre that raises body clearance by roughly 1.2mm according to the manufacturer.

Use this aluminium kit to tighten rear driveline alignment and to gain small adjustable changes to rear shock geometry on TRX-4 rigs; always verify clearance with pendulum wheels and follow standard installation checks.