By Jim Bolton (amcjrb@aol.com)
December 1999
Copyright 1999 Jim Bolton. Unauthorized reproduction prohibited
While no-one can deny that the AMC Eagle 4wheel drive system is very capable both on and off the road, some folks like the extra 4 wheeling capability of a low range transfer case.
The AMC Eagle used 3 transfer cases in its 9 year production run. These cases were manufactured by New Process and were designated models 119, 129 and 128. The 119 was 4 wheel drive all the time, whereas the 128 and 129 were switchable to 2 wheel drive. The 119 and 129 used a viscous coupling differential unit in the case, which allows some slippage between the front and rear output shafts and allows use of 4 wheel drive in any road conditions. The 128 case used an open differential to allow slippage. The differences in these methods of differentiation can be likened to the differences between a limited slip rear-end and an open rear-end. A worn out viscous coupling will behave much like an open differential.
A switch to a low range case offers two advantages. One is the obvious lower range for better 4 wheeling capability, the second is that low range is almost invariably low lock. That is, the front and rear outputs are locked in tandem and power is always evenly split between the front and rear axles. This means that even if both front wheels are off the ground, the vehicle can still move provided there is traction in the rear. Ideally, the viscous coupling should also behave this way, but after some wear, they will not.
Some common swaps for the Eagle cases are the NP 219, 229 and 242 transfer cases. The 219 was found in Grand Wagoneers in the Early 80’s. The 229 was found in the Grand Wags from 80 right through to 1991 and also in some 84 XJ’s (downsize Cherokee and Wagoneers) with the selec-trac option. The 242 is uses in XJ’s from 87 on up with automatic transmission. The NP228 case will also swap, but is less desirable because it does not utilize the viscous coupling (like the 128 in the Eagle).
New Process (now New Venture) cases are easily identifiable by a red tag riveted or screwed into the backside of the transfer case near the oil fill hole. The tag is embossed with the case designation and the low range ratio. Most low range cases are in the 2.6 or 2.7 to 1 reduction range. The cases are aluminum, and chain driven.
The Eagles all used the 23 spline transfer cases, regardless of the transmission they were used behind. This is different from Jeeps, which also used a 21 spline case, typically found behind 4 or 5 speed standard transmissions.
A couple other cases worth mentioning are the NP207 and NP231 cases. These are found in XJ’s and Wranglers with command trac. Although they will swap into an Eagle, these are part-time cases and cannot be used in 4 wheel drive unless the road conditions are slippery. Also, because these cases use a slip yoke output shaft, so driveshaft modification will be required. In my opinion, these are less desirable than the full-time cases because the ability of the Eagle to motor along in 4wd on bone dry pavement is one of the reasons I like mine so much. No need to shift in an out of 4wd as road conditions change. When October rolls around, you can just put the car in 4wd and leave it.
| 119 | 128 | 129 | 207 | 219 | 228 | 229 | 231 | 242 | |
| Found in | 80-81 Eagle | 86 Eagles | 81 - 88 Eagles | 84 - 86 XJ's | '80's FSJ | 85-86 Jeep XJ's | 80-91 FSJ | 87 - up XJ's and Wranglers | 87 - up Jeep XJ's |
| Full-Time High | Yes | Yes | Yes | No | Yes | Yes | Yes | No | Yes |
| High Lock | No | No | No | Yes | Yes | No | No | Yes | Yes |
| Low Range | No | No | No | Yes | Yes | Yes | Yes | Yes | Yes |
| 2wd | No | Yes | Yes | Yes | No | Yes | Yes | Yes | Yes |
| Viscous Coupling | Yes | Open Differential | Yes | No | Yes | Open Differential | Yes | No | Open Differential |
notes:
FSJ’s refers to the big Jeeps, up to 83 Cherokees and Wagoneers, as well as Grand Wagoneers
XJ’s refers to the little Jeep, 84 and up downsize Cherokees and Wagoneers, as well as Comanches (though technically, Comanches are MJ’s)
The exact definition of Full time 4wd and Part time 4 wheel drive elicits a lot of discussions. For purpose of this exercise, I consider a full-time case one which can be driven in 4wd on dry pavement, and a part time case (high lock) one which cannot be driven on dry pavement in 4wd, regardless of whether or not the vehicle has a two wheel drive option. Some folks consider any case which can be switched into 2wd mode a part time case. A part time case must have a 2wd option to be street driven, whereas a full-time case will often have 2wd, it is not required to be street driven. So long as you understand the features of the case and how they need to be used, what they’re called is not important.
Okay, so now you’ve found the case you want at the boneyard. You will want to make sure it works okay by running it through the ranges and checking the operation of the unit. Verify that in 2 and 4wd, the relation between the front and rear outputs is as expected. In 4 low, you can grip the front and rear output yokes and try to spin them in opposite directions. If you can, the case is junk. In 4 high, if the case is open differential (like the 228) you can spin the shafts in opposite directions with some resistance. With a viscous coupled case (like a 219 or 229) you should encounter a lot of resistance when trying to spin the outputs in the opposite direction. If you can do it by hand, suffice to say the viscous coupling is junk. It should take considerable force to do (ed. note - TSM's indicate 25 foot-pounds of torque). If the viscous coupling is junk, you can either find a different case, or not worry too much about it. Even if the viscous coupling is junk, your no worse off than with an open differential case anyhow. It is your call. Or you can swap the viscous coupling from you old 119 or 129 case into the new case (if your old one checks out ok).
Ok, you have a replacement transfer case, now you need to remove yours. This procedure should take a couple of hours, it is good to have a friend to help you. Remember, this process is dangerous, and your safety is your responsibility. You will need to raise your car and support it safely on jack stands. Then remove the transfer case skid plate. There is no need to drain the transfer case, but you may want to anyway. The next step is removal of the speedometer cable. It is removed by unbolting the fork that holds it in place and then rotating the speedometer (using the forks or a screwdriver) Then pull it out. Some fluid will come out so be ready. Next remove the driveshafts. The rear can be unbolted from the case and swung out to the side. Its better to completely remove the front driveshaft, however, as you will need room in this area to access the 2/4wd shifter. Remove the bracket and the vacuum shift motor (if your case is a 128 or 129). The transfer case attaches to the transmission adapter using 6 nuts (5 if you have a manual transmission). The top bolts are tough to get to. A long extension may help. If that doesn’t work, you can support the transmission and transfer case and unbolt the cross member from the body. Then you can lower the transmission and transfer case for added clearance. You must support the assembly however, or else the engine can tip back far enough in the engine bay to contact the firewall. Another trick is to unbolt the floor shifter (on auto cars) and reach through the hole to access the top nut. Its up to you to figure out how to get the transfer case safely to the ground. Its dangerous. I have used a floor jack (big one) with success. I pulled one in the junkyard and used an unmounted tire to cushion the blow and let it drop while laying a safe distance away.
Depending on the Jeep your case came out of, the front and/or rear yokes will need to be swapped over from the old case to the new. The procedure is easy, you need a big socket and breaker bar. The yoke nut size varies, but they are all pretty big. You will need hold the yoke, a pipe wrench can work, or you will need to buy or fabricate a tool to hold the yoke (this shown in detail in both the Jeep and AMC Shop manuals (TSM). The thread is standard right handed.
The other modification is to the transfer case rear output shaft housing. Or actually, to the rear of the case. If you lay your old and new transfer case out side by side, and look at the location of the speedometer hole, you will see that the Eagle output shaft housing is rotated about 30 degrees counter clockwise with respect to the Jeep case. This is necessary so that the Eagle speedometer cable will clear the floor. You cannot use the Jeep transfer case housing as is, as t he cable will break (ask me how I know). You cannot just change the output shaft housing, it is identical, the difference is in the rear case half.
You have three options
- Split your old case in half, split your new case in half and swap the rear case halfs. Its not as painful as it sounds, but there you need to be careful. If you choose this route, first remove the tailshaft housing and speedometer drive. Then remove the bolts that hold the case half together. When you split the case, hold down on the output shaft, if it comes out with the case half, you are going to have some roller bearings fall out. Not lethal, but easiest if you hold the shaft in. Carefully review the old and new case halfs to see that they are identical. On the 129 to 229 swap we did, we drilled out one hole oversize from the 129 case to match the 229. It may not have been necessary. One word of caution here!! Be very careful when your working inside the case. There are hundreds of bearings waiting to fall out and incapacitate your new transfer case. Ask me how I know!
- Drill and the Jeep transfer case back half to relocate the output shaft housing. This is best accomplished if your remove the case half as above. On the 219 case I prepared, the bosses for the other set of holes is there, you need to drill and tap. On the 229 case I did, the holes were already there, but were not tapped. I would strongly recommend that if you choose this option, you remove the case half, so you can align yourself properly before drilling. One wrong move and there is a hole in your new case.
- The third option is to re-drill the output shaft housing to relocate the housing. This option sucks, cause you can only reuse 5 holes, instead of 6. I did this on my first swap cause the case was already installed before I realized the problem of the speedometer gear interference with the floor.
Some folks have suggested that you can avoid this problem all together with a 90 degree speedometer cable adapter, but I have no firsthand knowledge as to whether this works.
Of these options, the first is the easiest for the do-it yourselfer, but it does require that you take apart and disable your old 119, 129, or 128 case. I’d rather keep mine whole as a spare.
So, if you have adapted your new case with the proper yokes and relocated the tailshaft housing all that’s left to do is re-install.
Reinstallation is simply the reverse of removal. No really it is, it helps again to have a friend who can help you get the case lined up. Some of the early 119 and 219 cases use 10w30 motor oil for lube, some others use automatic transmission fluid (dexron III).
Again, as mentioned previously, the 207 and 231 will require additional mod’s to either the driveshaft or the output shaft to mate up with the Eagle stock hardware.
This is where the engineering skills come to play. Of low range cases discussed earlier, only the 228 and 229 will utilize your original eagle vacuum shift motor (as well as a lever). The 229 uses a vacuum shift for 2 and 4 wheel drive, and a lever for high and low range. The rest of the cases use a lever only. The lever to shift your case can be homemade or adapted from the a Jeep shifter. The XJ’s used a neat looking lever with a black and orange handle. It works well but does not fit in the Eagle floor well. The FSJ’s used a small black handle that is close to the floor and mounted on the transmission tunnel. It is a better fit for an Eagle floor pan. It tucks in nicely nearly under the seat and looks factory correct. If you are using a 228 or 229, remember that you cannot engage low range unless you are fully in 4wd, and you cannot engage 2wd unless you are fully in high range. Adjustment of the shift mechanism is critical to retaining all functions.
If you have a mid 80’s Eagle with a front axle disconnect, you have some added work to do. The disconnect is a vacuum motor coupled to a set of forks which operates by sliding a splined collar on the front axle to engage or disengage a two piece splined front axle. It gets a little confusing, but if you are using the 228 or 229 case, you can continue to use your front axle disconnect as it is (assuming it functions correctly). If you want to use the 207 or 231, you must modify the front axle disconnect to work with the vacuum switch which is located in the transfer case. Unlike the Eagle, these cases use a lever to engage 4wd, which then opens a vacuum port on a switch located on the transfer case which connects the front axle. If you are using a 219 case, you must eliminate your front axle disconnect altogether. This isn’t a bad plan anyway regardless of which case you are using, since the factory eliminated the front axle disconnect on the last Eagles anyway. It greatly simplifies the function of the 4wd system and eliminates one of the more problematic components (the front axle shifter) It also allows the vehicle to "shift on the fly".
(Ed. Note: I converted my '84 Eagle to shift on the fly by simply shifting the car into four wheel drive, and then removing the red vacuum line from the axle shift motor and plugging the open ends on the line and the shift motor. For more information about the vacuum shift system, see Select Drive troubleshooting.)
Elimination of this front axle disconnect is easy (for transfer cases other than the 128, 129, 228 and 229). One method is to shift the axle into 4 wheel and remove the harness. Another is to shift it into 4wd and then plumb a constant source of vacuum into the appropriate port to keep it in 4wd. The method I prefer is to remove the shift motor, push the collar into connect mode, and then slip a hose clamp around the axle shaft to keep it from sliding out. This is cheap and won’t leave you wondering if your front axle is going to pop out of 4wd. Then you can either align the forks and replace the cover, remove the forks from the cover and replace it, or fabricate your own cover plate.
If you want to eliminate the front axle disconnect and you are using a 128, 129, 228 or 229 case, you must reroute the vacuum hoses such that the vacuum switch will still operate the transfer case vacuum motor.
Well that should be it. Your best bet to verify the operation of your case is to put the car on jack stands and try out all of the ranges. Verify all functions work correctly and you are ready to go wheeling.
Jim Bolton
Amcjrb@aol.com
Please be aware that the author, editor and web page host(s) assume no responsibility for any errors in this text. Also, your safety during these procedures (also before and after) is your responsibility.
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