Many of us are familiar with the failure-prone central-axle disconnect (CAD) unit in the front axle on YJ's. Many know how frustrating it is to lose four-wheel-drive when you need it most. So we have some options.
1. Replace the failed part in the CAD system.
For me that part was the vacuum line. I had no idea where that small hole in the vacuum line was. Doing this works, but you still have all the other 15-23 year old parts, that can conk out whenever. Plus, the parts aren't cheap.
2. Posi-lock or homebrew variant.
This is a better idea than above, as it puts the control in the hands of the driver, instead of the vacuum system. The cons to this are it retains the relatively weak axle shafts, mainly the two-piece passenger-side shaft. Also, it doesn't simplify the 4WD very much, it still retains the CAD system.
3. Swap in TJ/XJ shafts.
This in my opinion is the best option, as that's what I chose to do. The cons to this are the install is somewhat involved, you have to make a backing plate for the vacuum motor hole as well as seat a seal. Not too hard, but more involved than the other two I think. Also, your driveshaft will spin all the time, so it will likely need balanced. The pros to this are strength and simplification. Getting TJ (or '96+ XJ shafts) will give you larger 297x u-joints, as well as larger ears on the shafts. Also, it gets rid of the CAD system, which is the start of the whole problem.
This write-up will include a follow-along on how I changed my shafts from stock YJ shafts to stronger and simpler XJ shafts, and all modifications and special procedures. This is not meant to be a detailed instruction list, just something to help a fellow jeeper along.
Parts You Will Need
- TJ or 96+ XJ shafts
- Dana 30 Driver's side seal
- Sheet Metal (for cover plate)
1. After chocking the Jeep and getting it on jack stands, remove the tire. Remove the cotter pin with a pair of needle-nose pliers, and make sure you don't misplace the nut retainer in there.
2. Next to come off is the brake caliper. Using a 13 mm socket, remove the two bolts on the back of it. Pull the caliper off, and using a zip tie or something, secure it up and out of the way. Otherwise, lay it in front of the knuckle on the tie rod.
3. Pull the brake rotor off the wheel studs, and lay it out of the way.
4. Now's the time to get out the power tools. You need to remove the axle nut, and its ON there! You can do it with a breaker bar though, but if you have the power tools to do so, then use them. Using a 36 mm six-point socket, back that bolt out. If you don't have one, its something you can pick up at your local auto parts store for $10 or less. Make sure to get one rated for impact wrenches, because you'll be on that sucker. When you put it back on, it is supposed to be torqued down to 175 ft/lbs.
5. After removing the axle nut, There are three bolts on the back of the unit bearing. These are 13 mm twelve point bolts, and are torqued down to 75 ft/lbs. I would use a 1/2" drive set for these, as they are torqued down to a bit more than that. As a side note, leave the keys in the ignition to the first click, so you can turn the tires to get a better angle on the bolts.
6. To remove the stuck bearing, you can use a prybar and a hammer, just be gentle. Small hits in the right places will pull it out easily. When you put it back together, make sure to use anti-seize on the contact portions, it will make it MUCH easier to remove next time.
7. Make a note of how the dust shield goes on, and which side is which (if you're doing both sides simultaneously). Lay that off to the side with the pile of other stuff that you removed.
8. Now its time to take care of the CAD housing. Unplug the vacuum lines from the motor, and plug them with bolts. Tie them up and out of the way for now. The motor is held on with four 11 mm bolts. Make sure that before you start removing that, you have an oil drain container below it to catch the gear oil that comes out. It'll get messy, just a warning. Also, the small skid plate for the cylinder comes off with two 13 mm bolts, but the one on the right needs an angled socket to get to it.
9. Once the housing is out, slide the outer shaft out and remove the collar on the shaft. Pull out the intermediate shaft as well. Remember that prybar? Use it to remove the seal. Its located on the right side of the CAD housing. Mine came out fairly easier than I expected, but then again, I didn't know what to expect.
10. Seating the seal comes next. This is where ingenuity comes in handy. Normally to seat the seal, you have to drive it in from the carrier housing. That means a heck of a lot of work, not fun. What we rigged up is a simple tool that pulled the seal in as we wrenched on it. It consisted of a threaded rod with a nut and large washer (4"+ in diameter) on the knuckle end of it, the seal, a smaller washer (the size of the seal), and a nut (parts going from the outside in). As you would tighten the nut on the outside, it would drive the seal towards the outside, where it needed to be seated. Its hard to describe, check the pictures.
11. Once the seal is seated, you need to make a cover for the motor housing. Easiest way is to take off the seal, trace in on your metal, then cut it out with a sawzall. Drill out all four holes, and use the bolts from the motor housing to rebolt it back on, using RTV to seal it well. Here's a pic of mine.
12. Now, put it all back together! When you slide the new shafts back in, it is recommended you grease the splines and the spot where the seal rides. When you slide the shaft back in, make sure to support it right at the end of the axle tube, to prevent catching the seal.
You will need to fill the differential back up with gear oil, almost all of it will drain out. Look on the bright side, you're doing two jobs at once!
To rehash, the factory torque specs are 175 ft/lbs for the axle nut, and 75 ft/lbs for the unit bearings. The calipers are torqued to 11 ft lbs.
I sure hope this helps anyone who thinks this job is too intimidating.