All 1987-1995 YJ Wranglers and many XJ Cherokees came with a reverse-cut Dana 30 front axle that has a Center Axle Disconnect (CAD) feature. This can be easily identified by a medium-size cast housing integrated into the passenger side axle tube. This assembly uses a two-piece long side axle shaft that disconnects from the passenger front tire when the vehicle is in two-wheel drive.
There are a couple of issues with this design. First, it's not as strong as a one-piece axleshaft. Second, the vacuum-operated system often stops working for one reason or another, which leaves the vehicle stuck in two-wheel drive. Lastly, it really doesn't serve much of a purpose because the axleshafts still spin (so there's little reduction in drag) and the transfer case does not send engine power to the front axle in two-wheel drive anyway.Luckily, it's easy to upgrade the two-piece design to a much stronger and more reliable one-piece design. The inner axleshaft from a TJ or non-disconnect XJ will slide right in. However, you must have a way to seal the housing in order to prevent gear oil from leaking out of the passenger side axle tube.
Rusty's block off plate and seal kit includes everything needed to seal up the axle when converting a CAD axlehousing to a one-piece axleshaft. The block off plate replaces the vacuum-actuated fork housing, and the kit also includes an inner axleshaft seal. Rusty's takes the guesswork out of sealing up a CAD axle with this kit!