Motobilt Back Half Frame Kit MB3001 for Jeep YJ rear bumper with d rings weld on side plates and passenger and driver side two piece frame rails shown as a kit

Motobilt Back Half Frame Kit MB3001 for Jeep YJ drivers side view installed on green Jeep yj with roll cage tied into the rear portion of the frame

Motobilt Back Half Frame Kit MB3001 for Jeep YJ rear bumper with d rings installed on a green TJ view from the passenger side rear with no axle or suspension installed

MB3001

Back Half Frame Kit for Jeep YJ

Name: Back Half Frame Kit for Jeep YJ
Brand: Motobilt
SKU: MB3001
Price: 679.00 USD
Availability: InStock
Rating: 5.0 (1 reviews)

$679.00

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Product variants

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Back half frame kit for Jeep YJ designed to replace the rear frame section, creating space for coilover suspension while improving rear clearance and departure angle.

Assembly Instructions

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 once suspension travel increases or the axle position changes.

When building a YJ for more capable off-road use, the rear frame quickly becomes a problem. The factory frame rails sit inside the wheel area, limit shock placement, and drop low behind the axle, reducing departure angle and usable suspension space.

The Motobilt YJ Back Half Kit replaces the rear section of the factory frame to correct these limitations. This system moves the frame rails under the rear floor and keeps them higher and more consistent from the axle rearward instead of dropping down like the factory design.

By doing this, the kit creates the space needed for proper suspension movement and shock placement while improving rear ground clearance and departure angle. The narrowed and raised frame layout provides a cleaner structure for building a more capable rear suspension system.

This is not a frame repair section. It is a rear chassis system designed for builders who need more room, better clearance, and a stronger structure than the factory frame can provide.

Like all Motobilt components, this kit was designed by builders who understand frame limitations, suspension packaging, and real off-road use.

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Get the Details

Find all the information you need to get the right part for your rig.

Important Information

Designed for Jeep YJ 1987–1995
Rear frame replacement system
Not a front half or mid frame section
Moves frame rails under the rear floor for suspension clearance
Maintains higher frame rail position behind axle
Creates room for coilover shock packaging
Improves departure angle and rear ground clearance
Includes integrated rear bumper with d-ring mounts
Requires cutting frame and rear body modification
Requires fuel cell conversion
Not compatible with factory fuel tank
Ships bare steel and must be coated before installation
Requires welding and fabrication

Which Rear Back Half Kit Do I Need?

This comes down to what chassis you’re starting with and whether you are stretching to an LJ length body.

If you have a Jeep TJ, run MB3008
If you have a TJ and want LJ-length stretch, run MB3020
If you have a Jeep YJ, run MB3001
If you have a YJ and want LJ-length stretch, run MB3067
If you have a Jeep LJ, run MB3020-S or MB3020-W

Product Specifications

Vehicle Fitment

Jeep YJ 1987–1995

Material

3/16 inch Steel Plate

D-Ring Mounts

3/4 inch Steel Plate

Frame Width

8-1/16 inch narrower than factory YJ frame

Weight

Approximately 75 lbs

Manufactured

Made in the USA

Notes

This is an advanced fabrication system intended for builders performing rear chassis modification on a Jeep YJ.
The factory frame must be cut at the beginning of the bend so the new rear frame sections can sleeve over the straight portion of the original frame.
The body should remain on the vehicle during installation so the factory center body mounts can be used to locate the kit properly.
Rear body trimming below the tailgate is required to allow the new frame rails to pass through the body.
A fuel cell is required since the factory gas tank will not work with this kit.
Motobilt recommends tying the roll cage into the rear frame rails for added support.

Frequently Asked Questions

What does a back half kit do on a Jeep YJ?

A back half kit replaces the rear portion of the frame to create more space for wheelbase stretch, improve departure angle, and allow proper shock and chassis packaging for more advanced off-road builds.

Is this a factory replacement rear frame section?

No. This is not a repair section for restoring a stock frame. It is designed for custom builds where the rear chassis layout is being changed for more clearance and suspension room.

Does this allow the wheelbase to be stretched?

Yes. Like a proper back half kit, it is designed to allow the rear axle to be moved rearward without the axle bottoming into the low section of the factory frame.

Will this work with the factory gas tank?

No. This kit requires a fuel cell. The factory gas tank will not work with this rear frame layout.

Why is a back half needed when stretching wheelbase?

The factory frame only has enough up-travel clearance at the original axle location because of the raised section over the axle. Once the axle is moved rearward, it ends up under the lower portion of the factory frame. A back half fixes this by keeping the frame rails high behind the axle.

Can I run coilovers with this kit?

Yes. One of the main reasons for this kit is to create the space needed for proper coilover shock placement and rear suspension packaging.

Does this include a rear bumper?

Yes. The kit includes an integrated rear bumper with 3/4 inch thick d-ring mounts.

Is this a bolt-on part?

No. This is an advanced fabrication system that requires cutting, fitting, and welding.

Should the body be removed during installation?

No. The body should stay on the vehicle so the factory body mounts can be used to help locate the back half during installation.

Is this part of the complete Motobilt frame system?

This kit can be used as a standalone rear chassis upgrade for a Jeep YJ, and it can also be used with the Motobilt front half and mid frame components when building a full frame system.