Performance Off-Road Accessories Heavy-Duty NP231 SYE
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.
Preparation / Disassembly
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.
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.
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.
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.
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.
All content is copyright 2001-2005, and unless otherwise noted content comes solely from the mind and keyboard of Jim "Yucca-Man" Langdon