Installation of the Tom Wood NP231
Slip Yoke Eliminator Kit

Special thanks to: J.R. Farrar

Items you will need for installation:
  • Heavy Duty retaining ring pliers (or equivalent) They will need to be the type with the flat tabs to open up a "C" shaped snap ring and need to open to at least one inch.
  • Flat head screwdrivers to be used in separating the case. 
  • Rubber Mallet 
  • Hammer
  • Flat Chisel (make sure it is sharp) 
  • Possibly a small three jaw puller and a length of threaded rod with nuts and flat washers assorted metric and standard sockets
  • 10MM 12 point socket
  • Wire brush or Scotchbrite pad
  • RTV (silicon)
  • LocTite thread locker
  • De-greasing agent
  • Oil absorbent rags
  • Oil 
  • Jack and jack stands

This kit can be installed with the NP231 transfer case installed in or out of the vehicle. We suggest removal of the transfer case with the 242 model transfer case.


Step 1

Secure vehicle - while dismantling the transfer case, you will be disconnecting both drive shafts. This will render both "P" Park in an automatic and leaving your manual transmission in gear, useless to keep the vehicle from rolling. Please block all tires before starting the installation. Drain the fluid from the transfer case. Always dispose of used oil in an environmentally safe and legal manner. The photo on the right shows the drain & fill plugs. The lower is the drain plug the upper is the fill plug. Remove the front drive shaft and the front out put yoke from the transfer case.



Step 2

You need to move the transmission/transfer case mount out of the way to gain access to the transfer case. Position the jack just underneath the bell housing. Bring the jack up far enough to just barely put pressure on the bell housing. Loosen and remove the 4 nuts that attach the transmission mount to the skid plate. These should be near the center of the plate and recessed. Next remove the 6 bolts that hold the skid plate/mount to the frame. Place the jack stand underneath the transmission mount and slowly lower the jack so the transmission mount is resting on the stand. Next remove the rear drive shaft. Remove the two metal bands that hold the rubber boot on the slip yoke (visible in picture). Then remove the 4 bolts and 2 straps holding the u-joint to the rear pinion yoke and remove the drive shaft


Step 3

Your transfer case should now look like one of the pictures on the right. You now need to remove either the dampener hub or the slinger/shield. These will be discarded. If you have the hub, you will need a small "Y" shaped puller and 3 very long (6.5" min.) bolts or a long enough piece of threaded rod to make the three bolts. The correct thread size is 6mm dia. 1.0 pitch but #12x24 machine thread will work. I do not recommend using a hammer to remove this hub as it could damage the speedometer bell housing. The shield can be rather easily removed by lightly chiseling the area in which the boot had originally clamped. Place the chisel perpendicular to the shaft but with the blade running axially as shown above. You will not need to cut completely through but nearly so. Do this step twice, each being 180 degrees apart (opposite sides). This will enlarge the inner ring and will allow the shield to be slid off the end of the shaft. Next you will need to remove the output shafts rear most seal. (Shown on right.) This is tricky, but if done correctly is not difficult. As you can see there is an outer lip on the metal seal. Carefully remove the seal using a mallet and chisel or flat head screwdriver. Direct the forces away from the housing as much as possible to prevent housing damage.


Step 4

Remove any retaining rings that you may find during this process from the main shaft. Main shafts are different, some have 2 and some only 1 snap ring. You will discard these rings. Leave the snap ring which supports the bearing in the tail housing. There is no need to remove the bearing or this larger snap ring.



Step 5

Next you will remove the speedometer housing. First, mark the orientation, then remove the speedometer drive gear. Remove the bolts, then pull the speedometer gear housing out and away from the transfer case. Please take your time and try not to damage either the tail housing or transfer case. Be patient and pry slowly.



Step 6

In the picture to the left, you will see how large the pump is that will be on the shaft when you remove the tail housing. Also you will see a pointer to the pickup tube for the pump. Be very careful when removing the pump to disconnect the pickup line by gently pulling it out. Remember this, because you will be reinstalling this pickup line into the pump upon reassembly.



Step 7

Next you will separate the rear transfer case half from the front. Remove all the bolts that hold the case halves together. One of the bolts may have a 12point 10mm head. Look around the perimeter of the case to find the two locations that you can insert your screwdriver to start to pry the case halves apart. Then gently work your way around the perimeter of the case halves with your screwdrivers prying them apart. When separating the case, watch for a spring on the shift rail. Do not loose it and make sure it goes back on before re-assembly.



Step 8

Grab the rear tail shaft, front out put shaft and chain. Pull them simultaneously rearward. Be careful and observant of where the parts are in the transfer case. You will have 1 shift fork attached to the shift rail. It is best to leave as many parts as possible in the case. If you do remove it, pay attention to how the parts fit together and their orientation in the case, This is very important.


Step 9

You will now take the output shaft to a bench where you can work on it. Here the old shaft is shown in a vice. You will remove the retaining ring that holds the synchronizer hub/chain sprocket to the shaft. Slowly lift off of the gears and set them down in their proper orientation. Slide the two gears onto the modified main shaft the same way them came off the old shaft, Replace the retaining ring. Make certain the snap ring seats properly


Shown to the left is a comparison of the old (bottom) next to the replacement (top) shaft.

Step 10

With the tail housing now removed from the transfer case, you can install the new seal. Spread a thin film of RTV/silicon in the seal bore and around the circumference of the new seal. The new seal will easily push in with thumb or finger pressure. This is to be expected. Push the seal in squarely untill the outer edge is flush with the outer edge of the housing or until you feel it "bottom out"in the seal bore. Also clean off any remaining RTV from the back side of the tail housing. Be sure to grease the inner sealing lip of the seal prior to installing the new out put yoke.


Step 11

Remove all remaining RTV from the 2 case halves and mating surfaces. Installation is the reverse of the removal.

Install the new shaft into the front half of the transfer case. Making sure to put the chain and all other parts in the proper place. You will want to slide the front and rear shaft into the case simultaneously.

Next coat the rear of the front case half mating surface with RTV making sure to surround the bolt holes. Don't forget to install the spring on the shift rail. Mate the two case halves together and replace all the bolts, tightening in an alternating cross pattern. We recommend Loctite on all bolts and nuts.

When installing the oil pump. Make sure to get the feed line into the pump, be careful and take your time.



Step 12

After installing the oil pump, coat the mating surface of the speedometer housing with RTV and reinstall it. The photo shown here is without the seal installed for clarity. Please again note that there are no snap rings on the out put shaft in the area behind the bearing. But the large snap ring remains in the housing. THIS IS CORRECT.

Reinstall the speedometer gear assembly. Make sure it is aligned as it came out.

Prior to installing the new yoke, spread a thin coat of RTV/silicon through the bore of the yoke. This will prevent an oil leak here. Install the new rear yoke. Use thread locker and tighten to 40 ft lbs.



Your assembly should now look like this.


Next install the front yoke and drive shaft. Fill the transfer case with oil to within 1/4" of the bottom of the fill hole. Please note that over filling can cause a leaking problem.

Install the new rear drive shaft. Check and correct if necessary for proper drive shaft geometry.

NOTE: To prevent drive shaft tensional vibrations your net "U" joint angle at the differential end should be less than 3 degrees. It will be better to leave the pinion tail a little downward rather than too far upward to allow for natural spring wrap.


Recheck all bolts and other attachments, correct as needed!

Your finished and Thanks Again!