The factory Jeep YJ frame is designed around the original rear axle location. It uses a raised section over the axle to allow upward suspension travel, then drops down behind the axle toward the rear bumper. This works in a stock configuration, but it becomes a limitation when the rear axle is moved backward to stretch the wheelbase.
Once the axle is relocated rearward, it is no longer positioned under the raised portion of the frame. Instead, it sits under the lower section of the frame rails. In this position, the axle will contact the frame during compression, limiting up travel and preventing the suspension from working correctly. The only way to compensate with a factory frame is to raise the vehicle significantly, which reduces stability.
A back half kit solves this problem by replacing the rear portion of the frame and keeping the frame rails high and consistent behind the axle instead of dropping down like the factory design.
The Motobilt YJ Back Half Stretch Kit builds on that concept by not only replacing the rear frame, but also extending it approximately 15 inches. This allows the rear axle to be moved further back while maintaining proper suspension travel without increasing ride height.
By keeping the frame rails high and narrowing the rear structure, this system creates the space needed to mount coilovers outside the frame and build a longer rear suspension system. The added wheelbase improves stability, increases traction, and allows better suspension geometry in technical terrain.
This system was also designed to allow a full conversion from a standard YJ to an LJ length body. The extended frame provides the foundation needed to stretch the body to match the longer wheelbase.
To complete the body conversion, this kit works with the following Motobilt components:
- 15 inch stretch corner armor (MB1170 or MB1175)
- Stretch rocker guards (MB1177 or MB1177-S)
- Boat side rocker options (MB1171 or MB1171-A)
- Extended inner fenders (MB5529)
- 15 inch stretch floor panel (MB1172)
These components were designed to work together so builders can convert a traditional Jeep YJ into an LJ length body with consistent fitment across the chassis and body.
This exact combination of components was used on the Motobilt El Jefe build. Many builders will recognize that vehicle, and this system reflects the same approach used on that project.
This is not a repair section. It is a rear chassis and stretch system designed for advanced builds where wheelbase, suspension layout, and chassis geometry are all being corrected together.
YJ to LJ Conversion System (Required Components)
To properly convert a Jeep YJ to LJ-length wheelbase, the following components are required:
- Rear Back Half Kit (MB3067)
- Stretch Corner Armor (MB1176, MB1170, MB1170-A, MB1175)
- 15 Inch Stretch Rocker Guards (MB1171, MB1171-A, MB1177, MB1177-S)
- 15 Inch Stretch Floor Panel (MB1172)
- Inner Fenders (MB5529)
- Drop Down Tailgate (MB1168)
- Fuel cell that will work with this kit and it is part number MB5074.
These components work together to extend the chassis, body, and wheel opening location to properly match a 15 inch wheelbase stretch.
