Traxxas TRX-4M Complete Low Range Crawling Transmission. This optional transmission is intended for the Traxxas TRX-4M to give your crawler an incredible amount of low range torque. Pre-Built, this transmission comes out of the box ready to be dropped in and driven. There are no gears to mesh or adjust and no parts to align. The assembly just bolts in as a complete unit for quick and easy installation.