These are the instructions for installing a Rubicon Express Slip Yoke Eliminator (SYE) kit onto a NP231 transfer case.

The tools you’ll need to install this kit are:

• Basic mechanics wrenches/sockets
• Circular saw with a STRONG metal cutting blade (not a sawzall) or a grinder with a cutting disc
• Center punch
• Hammer
• Electric drill
• Tap handle – for the 3/8″ tap.
• 1/8″ and 5/16″ drill bit
• 3/8″ and 5/16″ Allen wrenches
• Cutting oil (WD40 was used on this installation)
• Silicone sealer (VersaChem Automotive Black RTV Silicone Type 270 was used on this installation)
• Lock Tite

Kit contents:

• (1) – Bearing/Seal Flange
• (3) – Grade 8 M10 x 25mm Bolts
• (1) – Seal
• (1) – CV Output Flange
• (1) – Yoke Strap kit
• (1) – 3/8″ -24 Grade 5 Bolt and Washer *
• (1) – 3/8″ -24 Drill and Tap kit
• (4) – 3/8″ -16 CV Nuts and Bolts

Installation

Installation takes 2-4 hours depending on installer experience and the working conditions. The transfer case does not need to be removed from the vehicle which means the more room you have to work under the vehicle, the better.

Remove the driveshaft from the vehicle.

On the rear axle, this is done by removing (4) 1/4″ bolts and (2) steel retaining straps from the differential output yoke.

At the transfer case, simply pull the driveshaft out of the slip yoke. Some oil may spill from the transfer case when the shaft is removed, but not a lot.

The transfer case will look like this with the driveshaft removed.

Remove the tailcone section from the transfer case.

The tailcone is held to the transfer case by three bolts. Two of them are marked in the picture. Hopefully you can find the third one on your transfer case! 😀 Remove them.

The tailcone should pop/slide off the case/shaft. If not, lightly tap it on the sides with a hammer to nudge it free from the case. The only thing holding it in place at this time is silicone sealant.

The transfer case will look like this with the tailcone removed.

Seal the output shaft bearing surface to avoid contact with debris.

Rubicon Express suggested the use of duct tape. Reynold’s saran wrap was used for this installation and lots of it. Even more than what’s in the picture here.

Measure and mark the shaft so that 1″ of splined shaft will remain.

It might be wise to mark a little more than 1″ of shaft because too long is better than too short. If you cut the shaft too long, it can be shortened. If you cut the shaft too short, you’ll need a new one.

You will need a circular saw with a metal cutting/carbide blade. A sawzall will NOT work. A 4.5″ hand grinder with a cutting disc probably works best.

When finished, if the shaft isn’t “square” at the end, grind it down to make it square. NOTE: This does not mean to rid the round shape of the shaft by grinding it square… but you probably already knew that! 😉

Center punch the end of the shaft.

This will ensure the drill bit starts in the center of the shaft when drilling the pilot hole.

To make finding the center of the shaft easier, place the CV Output Flange over the cut-off shaft. This reduces the visible surface area from about 1.25″ diameter to 0.5″ diameter making it easier to find the center. (Next two photos.)

Make sure you hit the centerpunch hard enough to put a dent in the end of the shaft deep enough for a 1/8″ drill bit to sit in.

Drill the pilot hole in the end of the shaft.

This will ensure the drill bit starts in the center of the shaft when drilling the pilot hole.

This is done with a 1/8″ drill bit.

This step is easiest done with the vehicle raised 6″ on jack stands and the transfer case lowered 2″. With the vehicle being as high as possible, you’ll be able to sit under it and guage the direction of the drill. The pilot hole needs to be drilled into the shaft as straight as possible. Take your time.

The pilot hole needs to be 1″-1.25″ deep.

Bore out the 1/8″ pilot hole with a 5/16″ drill bit.

If you want to be safe, use a 3/16″ bit before moving up to the 5/16″ bit.

Make sure the final depth of the pilot hole is 1.25″.

Use a 3/8″ -24 tap to cut threads into the 5/16″ pilot hole.

Use cutting oil (or WD40) and keep the tap threads clean.

If you have never used a tap before, tapping threads into the pilot hole is NOT the time to learn. Either read up on how to correctly do this, watch a video, or practice on another piece of steel. The proper way to tap a hole is one full turn forward (clockwise) and one-half turn back (counter-clockwise).

Since the shaft is made of hardened steel, it would be safer to cut it in one-half turn forward increments otherwise you risk snapping the tap off inside the shaft. THAT WOULD BE BAD! It’s also advisable to use a high-speed steel (HSS) tap, though you can use a high-carbon steel tap if you’re extremely careful.

Press the Oil Seal into the Bearing/Seal Flange.

You will need a vice, bearing press, or similar tool to do this. The oil seal needs to be pressed straight in or damage will occur. It wouldn’t hurt to put a small amount of RTV sealant on the Bearing/Seal Flange where the oil seal will be seated just to ensure that no oil would be able to leak around it. It’s not likely this would happen because it fits quite snug once in place.

IMPORTANT NOTE: This should have been put into the Rubicon Express instructions because if you don’t do this simple step, you’ll ruin the oil seal after the first mile of driving, and your transfer case will leak oil until you install a new one. You need to lube up the rubber part of the seal where it will make contact with the CV Output Flange. Wiping transfer case oil on it with your finger will be adequate. Make sure to put oil all around the black rubber part of the seal. This is to reduce friction otherwise the seal will melt and tear.

Afters the Oil seal is pressed into the Bearing/Seal Flange, turn it over and run a bead of RTV Silicone along a circumferemnce just inside the three bolt holes. The bead should be about 3/16″. Allow about 10-20 minutes for the silicone to “skin”. (Sorry, the photo for this step got lost. :()

Install the Bearing/Seal Flange.

Remove the saran wrap (or whatever you used to protect the transfer case output bearing) from the transfer case output shaft.

Clean the surface near the bearing making sure there is no leftover residue from when the tailcone was removed.

Use three grade 8 M10 x 25mm bolts to install the Bearing/Seal Flange onto the transfer case. Apply Loctite to the bolts before inserting them.

Now would be a good time to apply RTV silicone to the remaining splines of the output shaft. This is to prevent oil from leaking through the CV Output Flange once it’s installed.

Install the CV Output Flange.

Slide the CV Output Flange over the output shaft splines and through the oil seal. Take care not to damage the seal. You may need to use a hammer to lightly tap the CV Output Flange down the shaft.

Use a 3/8″ bolt and washer to bolt the CV Output Flange to the output shaft. Use loctite to hold the bolt in place.

The installation is complete.