Viscous coupler replacement V2.0

This is a write-up of my personal experience replacing the Viscous Coupler on my '94 Laredo. You can thank my mechanically-minded friend Phil for the excellent photos, myself for the bad ones, and the fact this became a 2-person job at some points for where there are none. :grinyes:

Before I get started, here's some of the items I recommend to have on hand:
4 jack stands and a hi-throw racing jack
Replacement viscous coupler (duh)
4 replacement straps and 16 replacement bolts for the U-joints on the front and rear driveshafts (manual does not recommend reusing)
3-4 quarts of your favorite blend of ATF
A good socket & wrench set
A pair snap ring and a pair of lock ring pliers
A bottle of penetrant, brake clean, a tube of JB Weld and a tube of RTV
One good computane, rubber or dead blow hammer

Part 1: Even with a Haynes manual and a walk through you can screw things up!

One Saturday morning using nothing but a Haynes manual and the excellent walk through provided at http://www.masoncomputing.com/np249/ (http://ww.masoncomputing.com/np249/) my friend and I tackled the worsening problem of a bad viscous coupler prior to a family outing to Colorado. To do this enterprise, we put a tarp down and the Jeep up on 4 jack stands. There's a sticker on the stands that recommends not doing this, but all I have to say is just to be careful when raising or lowering the beast; we didn't have any problems by putting the jack stands on the front frame rails, then raising the back slowly by the differential on the rear, then reversing the process to bring it back down.

With the Jeep in the air, removal of the driveshafts was only hampered by the fact that the shafts had been on there for long enough for the U-joints front and back to require some mechanical persuasion (see the part about a mallet in recommended items?) before they let go. Before removing the crossmember underneath, remember to support the transmission with a stand or a jack. We expended the high-throw jack and regretted it later as we were pulling the entire case out this time around, and it would have been helpful raising and lowering the transfer case in and out of position. After disconnecting the speed sensor (on the tail housing) and drive sensor (tells the VIC Hi or Lo 4x4) and performing the ritual fight with the passenger-side top nut holding the case to the tranny, we wrestled the case off and were ready to replace the failing unit. Just an FYI: If you ARE pulling the case, be prepared to raise the transmission a bit to stave off the flow of fluid that will come out of it. . . I lost about 2 quarts before I could raise the jack up and the flow subsided. . . .

http://myweb.cableone.net/wkeck/JeepVC/IMG_0064.jpg

The tube coming off the front is the vacuum actuator for the front axle solenoid. We destroyed the clamp on the hose getting the case off the truck, so that necessitated a trip to hardware store for a hose clamp before we could call it job well done.

After cleaning the case, replacing the coupler, re-attaching the tail housing, and bolting the case back into the Jeep (all of which is covered in the above walkthrough, so I won't go through it), we drained the differential fluid and called it a night because at that point with off-and-on breaks to consult the manual or find a piece that I had forgotten, it was 10PM and we were 'tahrd' and the RTV needed time to cure. Next morning first thing, we top off the transfer case fluid and start to put everything back together. . . . big problem, the rear axle is suddenly 3 inches too short to fit back into the tail housing of the transfer case. . . . :banghead: :banghead: :banghead: :banghead:
After some debate, Phil reminds me that he had called me on the direction with which I had replaced the speedo gear on the tailshaft of the transfer case. Neither of us wants to pull the case again, and I had to go to work (yes, I went looking like a grunge monkey. . . I work phones for a bank, so who's gonna look at me???? :evillol: ) so the project's on hold again for another day. I really want to thank my buddy here because this was the 2nd day that the Jeep was taking up a stall of his garage, and I'm probably gonna be lucky if I can drag him into any other expeditions like this on a vehicle again. . . ;)

Part 2: It's not fun until you've cut holes in your Jeep

So, begining of the third day, Phil's come up with a plan. This is the actual walkthrough you'll want to pay attention to for a way to get at the viscous coupler without completely removing the transfer case from the truck. You just have to not be squeamish about cutting holes in it. . . . :dunno::dunno:

Plan of attack was to remove the console and cut a small access port (which would then be sealed until next time). This gets into the area where if your Jeep has airbags, you'll want to make sure you disconnect the battery first and wait a couple minutes because your getting into the airbag impact controller area. After removing the console (no in-between pictures, sorry, I was on my own and have only so many hands, people :P) you get something like this:

http://myweb.cableone.net/wkeck/JeepVC/IMG_0113.jpg

The metal box is your airbag controller. Manual says that if the battery is not disconnected, your airbag can go off. Bad news if your a leftie like myself. With the area clear, we referenced where the lock ring plate was, (ok, ok, we straightened that paperclip and dropped it through the bolt holes until we found an idea of where the plate was) then marked off an area on the floor with grease pen and pulled out the Dremel.

http://myweb.cableone.net/wkeck/JeepVC/IMG_0114.jpg

The cutting wheel attachment went through about 5 disks before the 3 sides of a suitable access port were made and the flooring peeled back to give access to the top lock ring plate that usually makes removal of the case from the vehicle a must.

http://myweb.cableone.net/wkeck/JeepVC/IMG_0117.jpg

The lock ring plate was removed with a T25 Torx screwdriver, the plate removed, I remembered there were in fact 4 bolts holding the tail housing to the main body of the case. . . .

http://myweb.cableone.net/wkeck/JeepVC/IMG_0127.jpg

. . . at this point, there was a bit of a 2-man coordinated effort as getting the lock ring loose from the top required a team effort from someone below the vehicle to pull the tailhousing off the case. . . so no pictures. . . sorry. . . but the end result was this:

http://myweb.cableone.net/wkeck/JeepVC/IMG_0131.jpg

Tailhousing is off of the case, and the viscous coupler is right there, ready to replace. . . . all we needed to do was reverse the speedo gear on the end, so no pictures of the coupler out of there, (refer to the above walkthrough for how to take the coupler off the tailshaft of the transfercase), and putting things back together is reverse of taking them apart, console included. We bent the cut part of the body back flat and ended up using a bit of JB Weld and some masking tape to repair the hole cut in the bottom of the Jeep, and it still seems to be holding well to this day. . . rear shaft fit right in soon as the gear was flipped around (note to those doing this: put it back in the same way it came out. . . take pictures, I don't care, but remember how things came out so they go in the same way!!!!!:banghead: :banghead: :banghead: :banghead: )

Total elapsed (estimated) time if this method had been used the first time: 5 hrs tops. Actual time because of my screw-up: 3 days off and on. Reaction: love being able to drive Jeep around town without it crow-hopping every time I turn. :D:D:D

If you have any questions or comments, feel free to post 'em. . . (praise, ridicule, don't care, just tell me what you think!) :feedback:

I've got an NV249 replacement that's a few years old so I figure I'll have to visit this issue someday.

Hindsight = 20/20 so you think more pictures as you disassembled or marking parts would have helped you get the speedo gear in the proper way first time?

I'll keep my comments to myself about cutting a hole in the floor.I'm a tech at a jeep dealer and what i did to get at the snap ring was buy a cheap set of snap ring pliers at sears and heat them up and bend them at a right angle.that makes it real easy to get the housing of the back of the t-case.We typically can replace one of those couplers in under 30 minutes with 15 minutes being about right.I guess I have to give points for creativity

Pictures and/or marking parts would have absolutely helped me avoid this mess, thanks for bringing up the painful truth. . . . :D

I'll admit I'm not as 'shadetree' as I'd like to think, so what you have here is the results of brainstorming from 2 people who really didn't want to wrestle that transfer case out again. . . . with the average tools that a Sunday mechanic might have.

Pictures and/or marking parts would have absolutely helped me avoid this mess, thanks for bringing up the painful truth. . . . :D


I hear ya. :grinyes:

You got any pics that show where the 4WD transfer switch is located? I'm getting tired of seeing that message on my VIC everytime I'm driving and look to see what time it is.