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4x4 Posi Loc Kit Install for the Jeep Dana 30 CAD Axle

Your Dana 30 Central Axle Disconnect (CAD) needs a more reliable shifting mechanism

Cable shifters for all kinds of central axle disconnect axles, including Jeeps, are offered by 4x4 Posi-Lok. When we found a 1986 Jeep Comanche pickup truck that had been sitting out in a field for a few years, it was no secret it was going to be a project. Once it was nestled into the shop, a 4x4 Posi-Lok was one of our first projects and was an upgrade that made this Comanche that much sweeter.

As the AMC era of Jeep began to phase into the Chrysler generation, along with it came the Center Axle Disconnect (CAD) Dana 30 axle offering shift-on-the-fly four-wheel drive. No longer would Jeep owners have to climb out of their Jeep to engage manual locking hubs. The new Dana 30 CAD axle featured a vacuum-actuated shift mechanism that was integrated into the front axle housing, and while it was perfectly good in almost all cases, it gained a reputation as being a very weak link in the chain. A simple upgrade from 4x4 Posi-Lok can fix that problem.

Installing a 4x4 Posi-Lok system replaces the vacuum actuator with a mechanical cable operated setup that can be operated from inside the cab. A pull of the 4x4 Posi-Lok cable connects the right front axle to the intermediate shaft using the shift collar and fork, and 4WD is engaged. The system also works well with lockers. When the front axle is locked, you can disengage the passenger side in order to make turns without wheel hop. Best of all, replacing the factory Dana 30 CAD system with a 4x4 Posi-Lok offered us a little peace of mind. Here's how the installation went.

Cable shifters for all kinds of central axle disconnect axles, including Jeeps, are offered by 4x4 Posi-Lok. When we found a 1986 Jeep Comanche pickup truck that had been sitting out in a field for a few years, it was no secret it was going to be a project. Once it was nestled into the shop, a 4x4 Posi-Lok was one of our first projects and was an upgrade that made this Comanche that much sweeter.
Starting in the 1986-1987 transition year, as Jeep was being taken over by Chrysler, the familiar Dana 30 axle went through a revamp that included moving the differential to the driver side of the axle, eliminating the manual lock out hubs, and utilizing a central axle disconnect (CAD). This is the vacuum motor that was designed to engage the front axle CAD when the transfer case is shifted into 4WD.
As we did our walk-around assessment of the new-to-us 202,000-mile Comanche, all of the grease caked onto the inner "C" of the knuckle made it apparent there was a leaky axle seal on the passenger side. Since we were doing the 4x4 Posi-Lok cable shifter system, it made sense to tear open the axle and replace the leaking seal too.
Have an oil pan ready when you remove the four bolts that hold the CAD shifter to the axle housing. Gear oil is shared with the differential to keep everything lubed. When we got ours apart, there was more than just oil. Unknown chunks of metal came out of the cavity and concerned. Luckily, there was no damage to the axle splines or shift collar.
Next, the outer axle shaft needed to be removed. To do this, the brakes must be removed and the 36mm nut taken off of the stub shaft. These old parts had been mated for quite some time and needed a little persuasion to come apart. After removing the three wheel-bearing bolts from the back of the knuckle, a three-jaw puller was used to separate the axle stub shaft from the unit bearing, while a chisel and hammer coaxed the unit bearing off of the knuckle face. Don't use too much force all at once. Slowly work at it so you don't damage or warp the wheel bearing. There were quality Timken unit bearings on this axle. They were nice and tight, so they were reused.
Once the axle shaft was removed from the housing, it became apparent where the metal debris found earlier came from. Similar to the connection of a manual transmission to an engine, the two-piece axle shaft design utilizes a pilot bearing to align the inner and outer axle shaft. The original pilot bearing had deteriorated and fallen apart. The debris found in the CAD housing was what was left of the needle bearings. It was a wrestling match to get the remaining bearing sleeve out of the pilot hole in the outer axle shaft using a die grinder and a slide hammer. Installing the new bearing is a breeze once the old one is out.
That was just the first half of the job. There was still the inner axle shaft that needed to be removed so that a new axle seal could be installed in the tube. To accomplish this, the differential cover needed to be removed to gain access to the C-clip holding the inner axle shaft in the housing. We have no idea how many miles were on the gear lube in that differential, but it was changed anyway.
The old axle seal was punched out using a scrap piece of tubing that was lying around the shop. After a couple of solid blows with a hammer around the circumference of the seal, it popped right out. Then the inner axle shaft could be slid out of the housing to make room for the new seal.
Installing the new seal can be a bit tricky. To be safe, order two or three seals just in case you screw one up on your first attempt. The extras can be returned if you don't end up using them. While it may seem straightforward, it is easy to damage the new seal during installation. It is important to press on the "frame" of the seal and not on the actual rubber seal portion of the assembly. We took our seal on a field trip to the exhaust adapter aisle of the local auto parts store to find a tube diameter that would sit perfectly down into the metal cup of the seal without touching the rubber.
There are specialty tools that are made just to install a seal like this into a CAD housing. Since this is not a job that we intend to do all the time and the tool is expensive, we improvised and created our own installation rig. It consists of a long piece of all thread, a couple blocks of wood, and the exhaust adapter trimmed down to fit the job space. While the axle shaft was out, we took the opportunity to install a new universal joint into the axle as well.
The jig and seal were set up into the axle housing. The pulling block (right) should be set up against the face of the axle tube inside the knuckle, and not against the knuckle. The knuckle will want to turn as the jig is tightened, instead of pulling on the seal. We tightened the jig a little at a time, paying attention to what was happening with the seal. There is a 99-percent chance it will not want to go in straight; if it's crooked loosen the jig and move it to the high side of the seal. You will likely need to adjust the jig several times before the seal will align in the axle pocket correctly. If there is any doubt about the integrity of the seal after installation, knock it out and use one of your spare seals on a second attempt.
With the 4x4 Posi-Lok kit, the shift fork is reused from the OEM vacuum unit. The fork is held in place by three E-clips. These can be a little tricky to remove, but some mechanic's picks and small needle-nose pliers got the job done. Inspect the fork and finger pads for excessive wear or damage. Replace the pads or the entire fork if deemed necessary. Our fork assembly was in good shape, so it was reused.
The new shift rail is integrated into the 4x4 Posi-Lok shift cable. There are three new E-clips that come in the installation kit to hold the OEM shift fork onto the new shift rail. Do not install this yet. The shift cable needs to be fished through the cab first.
The accelerator pedal is removed so that a hole can be drilled into the firewall for the cable to pass through. The instructions call for a 5/8-inch hole to be drilled 1 inch below the accelerator cable and slightly to the right. Be sure to check the engine bay side of the firewall for wires/tubes/brackets before you drill so nothing is damaged. After checking the cable routing in the cab, we also drilled a hole in the dash to mount the knob bracket so that the shift knob was accessible but not in the way of normal driving. The shift cable was then threaded through the bracket and firewall and routed to the axle CAD housing. Once the cable was through the firewall, we installed the provided rubber grommet in the hole to protect the Posi-Lok cable.
With the cable routed to the vicinity of the CAD housing, it is time to assemble the new Posi-Lok shift rail, shift fork, and shift housing. We first installed the 4WD light switch onto the right side of the housing with thread sealant, then worked on the shift fork. Take your time with the E-clips; they take some patience to install and are easily lost. This is also the right time to adjust the shift cable throw. This was done by screwing the cable in or out of the shift housing. When the knob in the cab is pulled out, the left-most E-clip should be just about touching the housing wall, indicating that the shift fork can fully engage the shift collar into 4WD mode. When the proper position was achieved, the jam nut was tightened on the shift cable against the housing.
The shift cable was properly adjusted, and the jam nut locked down, so now it was time to install the 4x4 Posi-Lok to the axle housing. Back inside the cab, we pushed in the shift knob. Under the Jeep, the shift collar was manually pushed to the right side (2WD mode) and then the shift fork was slid onto the shift collar.
The cork gasket provided in the kit should be put on dry with no sealant of any kind, as per the 4x4 Posi-Lok instructions. This is so the unit can be removed for any needed adjustments without destroying the seal. There is a threaded plug in the shift housing that can be used to prime the CAD with a little gear oil. This threaded hole is also used for a vent connection that some Jeep had located there from the factory. The 4WD light switch can be wired now too. One side of the switch gets grounded to one of the CAD mounting bolts, and the other side of the switch gets the wire routed up into the engine bay.
The electrical switch that turns on the 4WD light can be found by tracing the hard steel vacuum lines from the CAD unit up to the engine bay. Eventually it will lead you to the vacuum switch that operates the 4WD light on the dash. On this 1986 Comanche, the switch was on the passenger side fender, near the HVAC blower motor. The location of the switch will vary between models and years. This switch completes the ground circuit to turn the light on. We confirmed that we had the correct circuit by disconnecting the wire and grounding the harness side of the wire with a jumper wire. With the ignition key on, the 4WD light will light up on the dash.
After you have confirmed you have located the 4WD light circuit, cut the wire at a convenient location near the original vacuum switch (yellow stripe). Route the wire from the Posi-Lok unit so that it is clear of any moving parts or heat sources. Using the provided red electrical connector, strip and crimp the two wires together. Then zip-tie the new circuit to the vacuum switch to help remind you that the new connection is for the 4WD light in case you are trying to troubleshoot something in the future.
Back under the Jeep, we located the hard steel vacuum lines that the original vacuum motor was connected to. The open vacuum lines need to be capped off with the boots that came in the kit. If they are left open it will cause a vacuum leak when in 4WD.
With the installation of the 4x4 Posi-Lok complete, it was time to test the new system. We pushed in the red button and pulled out the knob at the same time. It didn't take much force to engage the shift collar. If the knob won't pull out easily, don't force it; the axle shaft splines are likely not lined up. Rolling the Jeep forward a little while continuing to pull gently on the shift knob will line the splines up and allow the knob to pull out as the shift collar slides into place.
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