Jeep XJ

My Jeep

Performance Off-Road Accessories Heavy-Duty NP231 SYE

After removing my rear RE driveshaft and finally experiencing a smooth, quiet ride I realized that it was time to look at other options for slip-yoke eliminators (SYEs) and driveshafts. The Performance Off-Road Center (PORC) SYE has been highly recommended on NAXJA and elsewhere, and the price ($169) was hard to beat for a replacement output shaft-style SYE.

Tools needed

  • Basic metric handtools
  • Floorjack
  • Transmission jack
  • Lockring pliers
  • Snapring pliers
  • Flat-blade screwdriver
  • Tranny fluid
Take the Jeep down to the carwash and clean out the underside. Not only does this help reduce the amount of gunk falling in your eyes, it cleans some of the oil and grease off, making the bolts accessible once again. Since I was going to install the SYE in conjunction with a tranny repair, I decided to remove the NP231 separately so I could get it clean and play with it a bit as I worked. There are six nuts holding the t-case to the tranny, but you have to remove the crossmember to get at the bottom one.
  • Shift the case into Neutral, and drain the t-case fluid into an appropriate container
  • Remove the front and rear driveshafts
  • Support the transmission with a jack or stand
  • Remove the crossmember. If this is the first time it's been removed, read this page first
  • Disconnect the front and rear driveshafts. This is also a good opportunity to replace the u-joints and grease the front shaft CV joint if needed
  • Unplug the wiring for the Vehicle Speed Sensor (VSS), vent hose, and any other wiring or vacuum harnesses still attached. Safely tuck them out of the way.
  • Remove the t-case linkage rod from the range lever.
  • Either support the t-case with a tranny jack and secure it in place or prepare to bench-press it to the ground. As I recall, the NP231 weighs approimately 65-70 pounds.
  • Remove the six nuts holding the t-case to the transmission. If you are removing this from an AW-4 automatic, be aware that there is an adapter piece between the t-case and the tranny body. Don't remove those bolts.

Preparation / Disassembly

Layout of the parts included with this kitThe first thing I noticed when I got the package from PORC was that the box says, "Made in Taiwan" on it. I hope that's just the box, as I forgot to ask about that detail when ordering.

After looking into it a bit further, I realized one reason that may explain the low cost; it appears that most if not all of the PORC SYE is made in Taiwan. While I appreciate the low cost and haven't heard any quality complaints, I'd prefer to keep my purchases 'Made in the USA' when possible.

Inside of the tailhousing Another view of the tailhousing Compare the size of the 32-spline PORC output with the stock 27-spline Shown to the left are a series of parts shots; including the tailhousing with the already-installed bearing and seal, Compare the size of the stock 27-spline output shaft with the much beefier 32-spline output on the PORC unit. The stock shaft has been cut short to accomodate the RE Hack-n-Tap SYE.

Pulling the front yoke

Prior to disassembly, you need to remove the front (and rear, if so equipped) output yokes. On stock Cherokees and Wranglers, the rear driveshaft should just slide out although some later models included a harmonic balancer that needs to be removed.

The front output yoke is held in place with a 1 1/8" nut. This should be on fairly tightly so I kept the yoke from spinning by inserting two bolts back through the holes in the yoke and wedging a long wrench between them. Then, when I had the breaker bar and socket in place I was able to squeeze the wrench and breaker bar together to get the nut off.

Once the nut was off, a 2-jaw puller was used to remove the yoke and dust shield.

Once the front output was off, I had to remove the drive flange from the Hack-n-Tap in much the same way. I added another arm to the puller for stability and popped that right off as well. The dust shield is still in place in this photo because I hadn't yet realiized that I needed to take it off as described below. Pulling the RE Hack-n-Tap
Twisting the dust shield off the rear output

If you are doing as I did, and replacing a Hack-n-Tap SYE with the PORC unit you might want to do this step before removing the flange. I didn't, and had to partially reinstall the flange to give me some leverage.

The rear dust shield is pressed onto the output shaft; I used two bolts in the flange with a breaker bar through them to hold it into place and began turning the dust shield with a pipe wrench. Give it a little pull to the rear as you are turning it - the shield isn't threaded so this helps pull it off as you twist.

Once the output yoke is off, there are several lockrings and a snapring that have to come out. Remove those, unbolt the tailhousing and carefully pry against the cast pads in the t-case to remove the tailhousing. Mine has been baked on there for 183,000 miles and wouldn't budge; yours may be the same so take your time. Also, if yours was assembled anything like mine was there is probably a healthy glob of black RTV in the pry points - just be aware of it and carefully work through it.


Top is the PORC unit, middle is the cut '96 XJ shaft, and the bottom is a stock YJ shaft (year unknown). The YJ shaft is actually slightly shorter than the uncut late-model XJ (and TJ) shaft. If you have followed my description of the various SYEs and the reason we need them, you'll remember that the longer, unsupported output shaft of the late-model XJ and the TJ helps cause those vibrations.

Notice the difference in the size of the output shaft to the rear of the mode hub - the left 50% of the shafts in this photo. Given two equal materials, the thicker one will be stronger and that's what I've heard so far about this gear too.

Top - PORC mainshaft.   Middle - Stock '96 XJ mainshaft, previously cut for RE Hack-n-Tap.   Bottom - Early YJ mainshaft
The obligatory comparison picture. The red line illustrates the mode ring snapring location

One of the first reassembly steps is to remove the mode ring snapring from the old mainshaft (see above pic for location), and swap the mode ring assembly over to the new mainshaft before securing it in place with a new snapring. I have had some problems with this kit as the mode ring snapring seems too thick to fit into the slot in the shaft. Looking over many of the related threads on NAXJA, I realized that this is not uncommon. Many of the installations used the stock snapring as it seems to be slightly thinner, but at least one owner has had a replacement mainshaft sent by PORC when it proved to be too small. In my case the snapring seems to just barely fit when installed on the shaft without a mode ring, but once I have the ring in place the edges of the snapring simply won't sit down in the groove. The stock ring was a tight fit, but with a little persuasion from a wooden punch I was able to seat it properly. Apparently I'm not the first one who found that out; it's been mentioned a number of times on NAXJA and in other writeups I've found. Even then it's not an easy install as the stock snapring is still microscopically too large for the space provided; some users have been able to lightly sand the snapring to reduce the thickness before it installs correctly..

Clean all the old RTV off the case halves, taking care not to drop scraps into the case. Install the mainshaft, chain and front output together as a unit. I did this with the t-case standing upright on the workbench so I actually lowered the parts into the case. To me, this seemed to be a bit easier when wiggling everything together than it would have been with the t-case still attached to the Jeep. Before actually installing the rear half of the case however you need to make sure the shift rod will clear the space provided by the tailhousing cover. Dry-fit the rear housing and the tailhousing onto the t-case and measure the shift rod as you cycle it through the options. The shift rod may have to be shortened slighly if it will hit the bolt in the housing. Early NP231s used a vacuum actuator that plugs into the housing; the bolt is provided for the rest of us. In my case the shift rod cleared just fine so no modification was needed.

Note:Make sure you lubricate all seals when assembling. I have heard of several cases of the PORC SYE leaking from the rear output immediately following assembly, and it may be related to a dry seal during installation.

Clean the mating surfaces of the t-case halves with rubbing alcohol. Add a small bead of RTV to the front case half and give it about 30 minutes to skin over slightly before carefully sliding the rear case half into place. Make sure the oil pump is seated properly and that the oil pump pickup tube is in place in the pump before closing the case. Bolt it down loosely and allow the RTV to cure before torquing the case halves together. Check the manufacturers directions to verify the skin time.

Using the snapring pliers, install one snapring on the mainshaft near the oil pump assembly and then slide the speedometer gear in place. Secure it with the second snapring and then apply another thin bead of RTV on the tailhousing. Allow that to skin as well and carefully slide that over the mainshaft and bolt in place. Install the speedometer gear housing as described on this page

Once the case is together, the majority of reassembly involves reattaching both front and rear yokes with their proper seals under the fastening nut. Without that seal, the case will leak once it is refilled.

Stopping Points
The bolt I pulled out of my '96 speedometer holddown was a 5/16"-18 but that wouldn't fit in the new PORC housing. I picked up a 16mm long M8x1.25 bolt today at ACE and it fits perfectly. Apparently PORC uses metric threads but there's nothing in the instructions mentioning this. I can easily see some unsuspecting soul ruining a good tailhousing because they forced an SAE bolt into a similarly-sized metric hole.

The bolts around the perimeter of the t-case are M10x1.50 but there are two or three lengths used in the original application. Since they appear to be open at the end, I doubt there's any reason to prevent your using all the same length; I opted to match the factory lengths on mine.

The two E12 Torx bolts at the top of the bellhousing can be replaced with 3/8"-16x1.75" bolts.

The four odd-headed bolts holding the front driveshaft to the t-case yoke can be replaced as well; use four Grade 8 5/16"-24x1.25" bolts on each driveshaft.

Final Impressions
Wow...after I got the PORC SYE installed and attached my stock front driveshaft in the rear, I took it for a little spin around town. Now granted, I had previously experienced some vibrations from the cracked bellhousing and the RE driveshaft, but on the road I had bad vibrations that coincided with vehicle speed. After the new SYE was in place, I could actually look in my rearview mirrors at 40mph and distinguish actual objects - no more driving a paint mixer!

Although I am still considering purchase of a larger custom shaft, using the front driveshaft in the rear of the Jeep means I don't need spares for both. The heavier tailshaft and housing also lend a good peace of mind as one less bit of gear that could break.

e-mail Jim
created: September 5, 2005
Updated November 15, 2005

All content is copyright 2001-2005, and unless otherwise noted content comes solely from the mind and keyboard of Jim "Yucca-Man" Langdon
Any changes or modifications to your vehicle are at your own discretion; I take no responsibility for your lack of responsibility