The factory Jeep LJ rear frame was never designed for long wheelbase, coilover suspension builds. The frame rails sit inside the body and behind the axle, which limits how far you can move the axle rearward. This creates problems with wheelbase stretch, suspension geometry, and departure angle once you start building a serious off-road chassis.
When you try to run a true four link suspension and larger tires, the factory frame becomes the restriction.
A back half kit solves this by completely replacing that rear section of the frame.
The Motobilt Jeep LJ back half kit removes the factory rear frame rails and replaces them with a new structure designed specifically for wheelbase stretch and proper suspension layout. By cutting off the factory frame and installing this system, you can move the rear axle rearward to match your build goals while maintaining a clean and functional chassis.
The new frame rails are moved from inside the body to underneath it and tied directly into the bottom side of the rear floor. This opens up the rear of the vehicle for proper link placement and allows room for coilover shocks, bypass shocks, or ORI struts. Instead of working around factory limitations, you are building the suspension around a structure designed for it.
At the same time, the rear bumper is repositioned just below the tailgate. This reduces rear overhang and improves departure angle, which becomes critical as wheelbase increases and the vehicle is used in more technical terrain. This version of the kit includes a wide rear bumper for builders who want full width coverage while still gaining the benefits of a raised, high clearance design.
This system is built with fabrication in mind. The upper and lower frame rail sections are joined during mockup so you can dial in placement based on your desired wheelbase and axle position. The wide rear bumper is built from formed plate and features 3/4 inch thick d-ring mounts that pass through the bumper and weld on both sides for strength.
Unlike some back half kits, this system does not require additional square tubing to complete the structure. The formed 3/16 inch plate design creates a strong and consistent frame layout while still allowing the builder to tie in additional bracing if needed.
This kit is built for Jeep LJ builders who are stretching wheelbase, running coilovers, and building a chassis that works both on the trail and in real world driving conditions.
Which Rear Back Half Kit Do I Need?
Choosing the correct rear back half kit depends on your Jeep platform and whether you are keeping factory wheelbase or converting to LJ length.
- If you have a Jeep TJ, run MB3008
- If you have a TJ and want LJ-length wheelbase, run MB3020 or this kit (MB3020-S / MB3020-W)
- If you have a Jeep YJ, run MB3001
- If you have a YJ and want LJ-length wheelbase, run MB3067
- If you have a Jeep LJ, run this kit (MB3020-S or MB3020-W)
This is one of the most important decisions in your build. The rear back half determines your wheelbase, axle placement, and how the suspension packages into the chassis.
Fitment Notes
- Designed for Jeep LJ platforms
- Can be used on a Jeep TJ when converting to LJ-length wheelbase
- Will NOT work for YJ conversions. Use MB3067 for YJ to LJ builds
- Choosing the wrong kit will result in incorrect wheelbase, body alignment, and chassis layout
