Well written instructions came with the kit
First I removed the transfer case from the transmission. This was pretty easy since they were both laying on my shop floor. I did have to jack up the transfer case to get to the bottom bolt. That seems a bit backwards as the top bolts are the hard one to get to with it installed in the Jeep.
Next I used my pressure washer to remove most of the dirt and grease form the outside of the case. There was all colors of mud. I am sure there was some from Harlan, Aetna Mountain and Golden Mountain as well as some other places still on there.
NP231 transfer case ready for SYE install
Next, per the directions, I placed the transfer case in 4 Low. Next I used a 1 1/8 socket on my air wrench to remove the nut on the front yoke and then removed the front yoke.
Front yoke removed
Next, using a 9/16 wrench I removed the selector lever. If I had not moved it to 4 low before removing, turning the nut would have shifted it there any way.
Shift lever removed
Next I removed the three 15 mm bolts that held the tail housing in place and tapped the tali housing off. This gave access to the snap ring that holds the main shaft to the rear bearing.
Removing the tail cone exposes the snap ring.
With that snap ring off, I removed the 10mm bolts that hold the output housing in place and tapped it off. The speedometer drive had been previously removed.
Output housing removed exposing the oil pump
Stock 231 output housing
Next I noted the locations of the three different types of fasteners that hold the two case halves together. All but one has a 15 mm head. Two of these have washers and go over the alignment dowels. For some strange reason there is one bolt that has a 10mm 12 pt head and is longer than the rest. It is on the top.
Note the location of the three different types of fasteners.
With all the bolts out, I used a flat blade screw driver to pry the case apart using the pry slots. I was careful not to pry anywhere else so I would not scratch the sealing surfaces.
At this point, some more fluid came out even though I had drained it earlier. I carefully separated the oil pump from the pick up tube and removed it.
After removing the rear case half, I inspected the chain and the magnet. Even though this Jeep shows over 220,000 miles on the odometer, the chain looked great and there was very little metal on the magnet.
View inside the NP231 with the rear case off
Next I pushed the front output shaft out and removed it with the chain. I inspected both the sprockets and the chain further. Still no visible wear.
Front output shaft and chain
Next I removed the main shaft from the case. I photographed the shaft so I would know the relationship of the mode selector and drive gear.
Main shaft with mode hub and drive sprocket
The snap ring was just a hair too big for my Craftsman snap ring pliers to open. So I modified the pliers by grinding off the stops just a bit so they would open wider. The snap ring then slid off easily. I was then able to slip off the mode hub and sprocket.
This being an early 231, I had to remove the caged bearing from the sprocket before I could reuse it on the new shaft. I used my ball joint press to press out the two bearings.
pressing out the roller bearings
I pre lubed the new shaft and slid the sprocket in place and then the mode hub. I installed the new snap ring from the kit.
Next, I slipped the new main shaft into position in the case. I then removed the old spline seal form the front input shaft and installed it with the chain. I decided to wait until the front yoke is ready to go on to install the new spline seal.
New main shaft in place
I then test fit the rear case half to see if the shift rail needed to be modified. Sure enough this is one of the ones that required the rail to be cut as it extends 1/2 inch too far.
Need to cut 1/2 inch off the shift rail.
I reinstalled the shift lever and moved the case through all its positions to see how the shift rail moved and saw that it only interfered in 4 low. I cut the extra shaft length with a cut off wheel on my grinder after marking the spot with tape.
Cutting the shift rail
I also inspected the oil pump and saw the pump housing seal was worn and needed to be replaced. I got a new one from Crown along with the proper RTV to seal the case.
New oil pump seal
After a final inspection, I applied a bead of RTV to the case and after letting it cure I put the two case halves together.
RTV curing onthe rear case half
Here is where I hit my first snag of the installation. The oil pump needs to be installed at the same time as the rear case so that the pickup up tube can be inserted into the pump. On a stock transfer case, you can slip the pup off the drive gear and get enough wiggle room to install the tube after the case halves are together. However, on the SYE shaft, the rear section of the shaft is bigger and stronger making it very hard to get enough room to move the oil pump.
There was a bur on the output splines that the oil pump has to slide across and working by myself, I could not hold the case steady and guide the pump down the sticky splines. I went ahead and assembled the case halves, thinking I could install the dip tube later as I always have on stock cases.
I had already torqued the case bolts to 25 ft lbs before I realized I was not able to move the pump like I was accustomed to. However, with some fishing with a dental pick and a small screwdriver, I was able to install the pick up tube and eventually get it seated in the pump. Next time I will get help if necessary to make sure the oil pump and case go together as a unit.
Oil pump in place
Next I placed one of the snap rings for the speedometer drive gear on the shaft, then slipped on the blue drive gear followed by the other snap ring.
Speedometer drive gear in place
Next I applied a bead of RTV to the new output housing. The Crown Kit comes with eh bearing and seal preassembled in the new housing. I torqued the bolts to 17 ft lbs.
New Output Housing
The output housing is drilled an tapped for a vacuum switch on the shift rail. However, the Jeep this case is going into does not use one and this kit comes with a handy plug. I noticed before screwing in the plug that the shit rail looked very close to the end of the hole. Sure enough on a test fit, the plug hit the end of the rail about one thread form being tight. I shifted the case around and found that if the plug was all the way in, the case would not fully shift into 4 Low.
I must not have cut the shaft short enough buy 1/16 inch of so. Rather than pull the output housing and cut the shaft again, I simply ground off the end of the plug. I had to remove about on thread to get it to clear.
Shift rail plug
Next I installed the two yokes and called it done for now.
Rear yoke installed
I used a spare speedometer drive gear to plug the hole until the case is ready to be installed in Jenny’s Jeep.
Slip Yoke Eliminated!
The next step will be to determine the best way to set the pinion angle as the pinion now has to pint at the transfer case instead of being parallel to the out put shaft. Our plan is to use a stock front drive shaft in the rear position.
Overall, I was very pleased with the quality of the Crown Kit and the well written instructions. I am not sure how much time I spent on this project as the time was spread over several days. The new main shaft is much larger than the original in the tail shaft and speedometer drive areas so in addition to being shorter, it also looks much stronger.
Note how much bigger the SYE shaft is than the original
Update: The case is now installed in Jenny’s XJ. It took approximately 8 degrees of shims to align the pinion with her three inch lift. The shift rail needed to have been cut shorter as the plug will bind the shifting into 4 low if screwed all the way in. I added a second O ring to cure it. Other wise it works great. See the write up for installing the SYE in the Jeep Cherokee here.
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