Sure, this issue may go down as one of the cheapest in Jp magazine history, but sometimes it may behoove you to blow a little coin on upgrades. But just in case you're living on bologna and peanut butter so your house doesn't go to the repo depot, we decided to bring you a couple different solutions to a pretty common problem.
All '87-'95 YJs and some early XJs have a Central Axle Disconnect (CAD) system on the passenger-side axle tube. It consists of a two-piece splined shaft and a coupler that is slid back and forth via a vacuum-operated shift fork to either connect or disconnect the shaft. The trouble is that the vacuum lines rot out, the vacuum motor can seize up, and the shift fork can break. Any of these problems will result in no front drive when the T-case shifter is pulled. Any of the options below will get you up and running in 4x4 again. We've included pros and cons of each, so choose your weapon and/or budget and get greasy.
Option 1 - Factory Parts
You can buy complete replacement vacuum motor assemblies on-line at quadratec.com. The large C-clip holds the motor shaft in the housing and the two smaller clips locate the shift fork. Prices were found at press time.
Cost: $78
Pros: Will get you going again for not much money and retains factory function. If you've got an open diff the spider gears will spin instead of the front driveshaft when the shafts are disconnected. Or, if you've got a limited slip or locker the CAD can help prevent unwanted feedback in the steering wheel.
Cons: Retains factory function and mess of vacuum hoses. Doesn't allow for driveshaft disconnect if you're running a locker or limited slip.
Option 2 - 4x4 Posi-Lok
The 4x4 Posi-Lok replaces the factory vacuum motor and hose assembly with a cable-actuated shift mechanism. The company offers two different cable lengths for stock or lifted Jeeps, so we've included our price for the longer cable since most Jeeps we encounter are lifted.
Cost: $210
Pros: Allows certain and sure engagement by pulling the in-cab knob. Allows user to disconnect front axle shaft in 4-Hi or 4-Lo. This allows 2-Lo if an open front diff is used or allows tighter turning if an automatic locker is used.
Cons: Requires retention of factory two-piece axleshaft, which in '94-earlier models with 260-size U-joints may not be ideal.
Option 3 - Drill and Pin Fork
In lieu of replacing the stock two-piece shaft with an aftermarket one-piece shaft, you can permanently pin the shift fork into the Locked position.
Cost: $1.50
Pros: Extremely cheap and chances are you've already got the right size bolt in your spare parts bin.
Cons: Retains small 260-size U-joints if Jeep is so equipped and doesn't allow for any disengagement if you're running a front locker or limited slip.
After drilling a small hole in the shift fork, we inserted a machine screw with a nut to hold it in the right position. Resist the urge to run a huge bolt since the larger hole can weaken the shift fork. A regular 1/4-inch bolt is fine since there's not that much lateral force on the fork once the collar is engaged.
Option 4 - Superior One-Piece Shaft Upgrade
Although Superior's premier Evolution Series axleshafts are more expensive, the company's Discovery Series shafts are made of top-quality alloy and feature rolled splines and induction-hardening like their more expensive counterparts. We replaced both front shafts, but you could replace just the passenger-side shaft at the price listed below.
Cost: $284 (passenger-side inner and stub shafts with Spicer 760 U-joint)
Pros: Upgrades earlier 260 U-joint shaft to larger 760 size U-joint. Has better metallurgy than any stock shaft, black oxide coating, and rolled splines.
Cons: Offers no method of disconnect for vehicles running a locker or limited slip, so some steering feedback may be noticed on the street.
 The 760 Spicer U-joint on...  The 760 Spicer U-joint on the left features larger U-joint caps and stronger trunions than the 260 Spicer U-joint on the right, not to mention a cold-forged body with strength to handle 35s. Superior includes full-circle clips for use with the U-joint rather than regular C-clips. |  Superior also offers this...  Superior also offers this cover plate so you don't need to retain the bulky vacuum motor. The best part is ripping out all the factory vacuum hoses. |  The stock CAD shaft has a...  The stock CAD shaft has a larger seal surface than the Discovery Series or a stock one-piece shaft, so you must remove the old seal and install the new one available from Superior. The inner disconnect shaft is actually a C-clip design, so you'll have to pop off the diff cover to remove the clip before the shaft will come out. |