My 1994 Jeep Wrangler Renegade, like others from its era, came with a vacuum-operated front-axle locker. The transfer case has a spiffy vacuum switch that, when the unit is shifted into 4H or 4L, applies vacuum to the locker unit to engage the passenger-side axle on the fly. Shift back to 2H, and the vacuum is reversed to disconnect the passenger-side axle. The trouble starts when any of the myriad of vacuum hoses breaks, or the vacuum unit on the axle gets sand/mud/crap in it and gives up the ghost, or all of the above. I'd like to congratulate whoever designed the unit for a really impressive bit of engineering, and then I'd like to take them outside and hit 'em with a brick.

I bought the Jeep used, and the vacuum hoses were already gone, which would have been bad enough had I known how the front axle locker operated, but I didn't, and thus I had no idea that when I thought I was in 4WD, I really wasn't. After several head-scratching episodes being stuck when I shouldn't have been, an observant onlooker noticed that my front wheels weren't spinning. This prompted some research (after getting unstuck, back home, and cleaned up), which resulted in my becoming a Certified Vacuum-Locker Repair Expert. I was able to jury-rig the non-functional vacuum unit, but it was not a viable long-term fix because it forced the front axle to remain engaged full-time.

I opted to purchase a 4x4 Posi-Lok Positive Axle Engagement kit from a guy on eBay, mainly because I knew good and well that nobody in Doha would have one. It came with instructions, but some of the photos were sort of lame, so I figured I'd post my installation story online for the benefit of anyone who might be staring at their stuck Wrangler, scratching their head like I was, and wondering what to do about it. This should give you a reasonably good idea of what's involved, and if you buy your own kit, it will (hopefully) contain all the details I've omitted.

First, a look at the kit. It contains pretty much everything you need, with a few notable exceptions. All the parts seem to be stout and of good quality--certainly better than the factory vacuum lines. Watch it when you cut the zip-tie that holds the cable in a coil--that cable is very stiff, and wants badly to be uncoiled!

Parking the Jeep with the passenger-side wheels on a curb makes this operation much easier, as it puts the gear oil at the other end of the axle from where I'll be working, plus it offers more under-Jeep room for my fat backside:

Get behind the passenger-side end of the front axle with an 11mm socket. Pull all the vacuum and electrical wires off, if they're still there (mine weren't), and remove the four bolts that hold the vacuum locker on the axle housing. About a quarter-cup of gear oil will fall out:

For the curious, here's a look at the axle locking collar, in the unlocked and locked positions, respectively:

You need the fork from the old mechanism. Note here the stack of washers I had installed on the shaft a couple weeks prior (thanks, monkeyevil!), to force the unit to stay in the locked position:

Removing the fork involves first either removing a large C-ring or prying the vacuum drum apart. This one was obviously all crapped out inside, which was why I had to install the washers, and frankly I enjoyed ripping it apart. Then remove the two small C-clips from the shaft on the inside of the main housing. The shaft will slip out, releasing the fork:

Voila, the fork. Check it for damage and wear. The company sells a cast-iron replacement fork if you need one.

Wipe your hands, get inside the cab, and figure out where you want to mount the pull-knob. The cable housing is very stiff, and you want to route the thing away from the exhaust and other hot stuff, so coming up with a good spot is not a cake walk. I settled on mounting it on the hump, just to the left of the transfer case shifter. Here's a look at the cable going through the hole I drilled in the firewall, with the grommet (included in the kit) already installed:

Back underneath, insert the end of the cable into the housing, slide the old fork onto the end of the cable, and install two C-rings in the close-together grooves on the shaft:

Slide the fork up against the second C-ring, and install the third C-ring:

Here's a look at the completed & installed assembly, with the 4WD indicator lamp wiring hooked up to the new switch. I coated the brass threads with black RTV silicone, and afterwards gooped silicone on the wiring connections (included in the kit) to weatherproof them. The only adjustment concern is to be sure that the cable housing is threaded far enough into the main housing so as to allow the collar to be completely disengaged when the knob in the cab is pushed all the way in, but not so far that the collar can't be engaged all the way (where the first C-ring hits the housing).

Now to route the cable housing. I zip-tied it to a bolt on the master cylinder to keep it away from the intake manifold:

And another zip-tie on a bracket below the air filter box, to keep it away from the exhaust and the steering shaft. I left this one a little loose, in case suspension travel pulls on the housing a bit:

One more hole drilled for the bracket bolt (included in the kit, with a nice nylon-grip nut), a small slice in the carpet, and the installation is complete! Pushing the red rubber button releases the cable to slide in or out, and the black knob can be screwed in or out if fine adjustment is needed. It's out of the way, right next to the transfer case shifter where it ought to be, and looks relatively nice.

Since I didn't need the transfer-case vacuum system any more, I disconnected the lines all the way back to the intake manifold. The T-connector was originally the take-off point for the transfer-case vacuum line, so I pulled it out completely and ran the remaining line (with the bit of orange hose) straight to the manifold. That's the master cylinder power-assist drum on the right, if you're trying to get your bearings:

Under the vehicle, on top of the transfer case, is a four-hole rubber connector with four vacuum lines running to it. I cut all four lines, sealed them with Goop (though RTV would work just fine) and replaced the connector on the transfer case. I then pulled out all of the related vacuum lines.

My 4WD is once again operational. I know, because the little light on the dash says so!