NP229/Dana44/Front Axle Disconnect...Scottie?

[Joe Guilbeau]

Scottie,

Please wade in here and correct my understanding of my 1983 Cherokee Laredo 2Wheel/4Wheel drive.

I have the Dana 44 Front Axle with the Front Axle disconnect vacuum motor.

I've replaced the AMC Corporate 20 Axle with a Limited Slip Dana 60, both now have 4.10 gearing.

My transfer case is a NP229, which I believe was introduced in 1983 as the Select-Trac.

Intrestingly enough, while the transfer case itself has a "Neutral" position, the shift lever only has the "High"/"Low" markings on it.

It is my understanding that when the Front Axle Disconnect vacuum motor is activated slides a collar over two parts of the front axle shaft so that both front axle shafts are driven at the same velocity by the front driveshaft, which is always turning the drivers side axle shaft.

In Two Wheel Drive, the vacuum motor on the front axle disconnects the collar allowing the passenger side axle shaft free rotation, while the driver's side axle shaft is engaged by the front driveshaft.

At the same time (2 Wheel mode), the transfer case is operating with an "Open Center Differential", via the Vacuum Motor on the transfer case. This allows the front and rear driveshafts to rotate at different RPMs, and the Viscous Coupler is not engaged.

When the vehicle is placed in 4 Wheel Hi, the vehicle is brought to a stop, and the switch inside the cab is operated by pulling the detent stop, and sliding the lever to the 4 Wheel Drive position.

I've read (your posts) that the shock load of engaging the shift collar while the vehicle is travelling is no good, since in 2 Wheel Drive the two front wheels may not be travelling at the save RPMs.

(when the truck has all 4 wheels off the ground and the vehicle is in 2 wheel drive, enging turned off... rotating a front wheel, causes the other front wheel to travel in the opposite direction).

Now in 4 Wheel Hi, at the same time that the front axles are collared together, the vacuum motor on the NP229 transfer case engages the Viscous Coupler somehow, which is filled with the fabled thixotropic silicon fluid and a series of interwoven plates that engage the liquid.

One set of plates are attached to a drum shell, and the other set of plates are attached to (the rear drive-shaft?).

So, in 4 Wheel Hi, the front axles shafts are coupled together, and my front and rear driveshafts are coupled together thru the Viscous Coupler.

When a rotational speed difference exists between the front and rear driveshafts, the two sets of plates inside the Viscous Coupler are spinning at different revolutions, thereby causing the silicon fluid to heat up, and thereby thicken.

This action attempts to limit the differential speed between the front and rear driveshafts, by shearing action of the silicon fluid between the plates via heating and thickening. There always remains some slippage, which prevents binding and presumably breakage.

With the Range Lever in the "Hi" position, the center differential is open, and the Viscous Coupler acts as a "Limited Slip" differential of sorts in the transfer case.

When the Range Lever is in the "Low" position, the front and rear driveshafts are somehow locked together, how exactly I am not sure, pretty sure it is gear meshing, but not understanding the theory.

I am an Electronic Tech, and understand valence theory, but mechanical gears and such remain a mystery.

I think that I have most of the above info right, but am interested in hearing your critique of my understanding.

The reason that I am posting this in this forum, is that there seems to some misconceptions on the NP229 and the Vacuum Disconnect motors and the theory behind them.

My rig is a daily driver, with the thought that I can get off road and return in some reasonable manner, without carnage occuring, I did enough of that in my 77 Cherokee Chief with the BW1339, Quadra-Trac and optional low range lock up.

So in my particular case, I suppose that I have a Limited Slip Rear Differential rear axle, an Open Differential (2 Wheel Drive mode) in the NP229, AND a Limited Slip Differential (4 Wheel Hi, via the Viscous Coupler) AND a Locked Center Differential (via a not understood locking mechanism in 4 Wheel Lo...2.61:1 gearing), while the front left drivers side axle is always connected to the front driveshaft, while the right passenger side front axleshaft is free to spin in 2 Wheel Hi, but is connected to the drivers side axle shaft by the shift collar activated vacuum motor on the front axle.

Have I got it about right? Its a wonder the thing gets from point A to B at all!

What about that 4 Wheel Lo when things seem to be locked up?

Any pointers and observations are appreciated, as I know that this thread has been presented in numerous iterations before, and I really want to understand the details.

JAG

[mdill]

You have it pretty much right,

The left (drivers side ) axle is the one that is dissconnected when in 2wd mode.
and the right side is always connected to the diffy.
In 2wd mode the 229 differental is not open, it is not connected or used at all,
power is directed to the rear output shaft directly bypassing the transfercase
diffy. In 4 hi power is still direct to the rear output, but now the transfer case diffy
with its wonderfull negitive temp coeficiant viscosity silicon goop comes into play
actting just as you said, coupling the rear and front output shafts together. In
4 lo, the diffy just gets locked out, (think of a air locker only this is spines and
shafts)

All the rest is dead on.

Mike D.

[scotty]

well,you are slighly confued on a couple of points. there is no open center diff in 2wd,only the limited slip viscuous coupling.

while the transfer case is in 2wd,the diff is locked somehow(i cant remember exactly how) and the front output removed from the equasion,essentially just like any ordinary part time transfer case.

in 4wd hi,it sounds like you have a pretty good idea of whats going on there-the silicone v/c acts as a limited slip to limit the amt of power that is allowed to spin thru to one shaft or the other.

it is a nice feature for a street driven rig,as in bad weather a person does not need to worry if the pavement is slippery enuff to remain in a locked 4hi. alot of people shift the 229 into 4wd at the beginning of winter and leave it there till spring smile.gif

the v/c does a very good job(like most limited slips) of keepig both its outputs(in its case the front/rear driveshafts) spinning the same as long as the traction difference is not too great. if one set of wheels is on slipperier terrain than the other,it is possible to spin all the power out to only one set of wheels-the set with the least traction.

in low range you are correct that both driveshafts are mechanically locked together,and spin at the same rate,period. an interlock pill keeps the transfer case from being shifted into low range in 2wd. in theory it would be possible to remove this pill and be able to use low range in 2wd,but i cant say for sure cause ive never done it,and it has been a very,very long time since ive had a 229 apart.

you are alittle confused about whats going on with the front axle as well. the pass side shaft is always spinning,as is the outer part of the driver side,since these shafts are directly connected to the hubs via the full time drive flanges.

in 2wd,the collar is slid over,keeping the 2 pieces of the driver side shaft seperate.

as the pass side shaft spins in forward motion,the spider and side gears are spinning inside the diff,while the diff itself and front drivesahft are not moving. because of the way the side gear rotates the spider gears,the inner part of the disconnected shaft is spinning backwards,opposite of the forward direction of the outer part of the sahft.

its just like how one tire spins backwards of the other when you jack up an axle and spin one wheel with an open diff.

while you are not saving any wear on most of the internals,this was an effort to gain alittle fuel economy,since the driveshaft is not spinning,kind of like unlocking the hubs. it takes considerably more effort to spin the whole diff and drivesahft,rather than the shafts simply spinning the spider gears.

when in 4wd,the collar slides over and effectively makes the driver side shafts into 1 shaft,at wich point the front axle is just like any other standard axle assembly.

when you stop and shift an 83/84 disco axle,229 equipped rig,in theory what is supposed to happen is this:

the vaccum switch routes the vaccum to the front axle shift motor,to the port that slides the collar over and connects the 2 halves of the driver side shaft. when this happens,the vaccum is then shifted to a port on the axle shift motor that sends vaccum to the port on the shift motor on the 229 to pull the lever into 4wd.

in theory,the 229 cannot be accidentally shifted into 4wd if the axle shift motor is not functioning as long as the vaccum is hooked up in the factory manner.

shifting back to 2wd simply applies vaccum to the ports on the axle and transfer case to move the collar back over(disconnecting the 2 piece shaft),and the shift lever back to 2wd.

the reason th 83/84 disco axle cannot be shifted on the fly like the full time axle rigs is because of the 2 pieces of the disconected shaft spinning opposite directions. as the splines line up,the coupler will very viloently engage the sahfts,and start the 2 pieces spinning the same direction ,and start the diff and drivesahft spinning. the result of shifting the disco axle at speed can be broken shafts,broken collars,and stripped splines. not good.

as was mentioned,applying vaccum permantly to the disco axle makes it essentially like any other full time driven axle. with the transfer case in 2wd,everything is still spinning,the diff,drivesahft,even the front output and chain in the trnasfer case. its just that the front output is not connected to the via the viscuos coupler. the center diff is locked in 2wd,and the front is not part of the equasion. the case could now be shifted on the fly,just like other year 229s.

anyway,hope that helps clear it up for ya smile.gif

further CAD questions? smile.gif

[ March 05, 2003, 08:33 AM: Message edited by: scotty ]

[Joe Guilbeau]

Mike and Scottie,

Thanks for the input, I am mechanically challenged, so I will read and re-read the post and study the exploded parts diagram of the NP229.

Always nice to know and follow what is happening as you tool down the road.

Again, thanks for the input.

JAG

[4DWUDS]

Just a little extra on those pesky vacumn lines.
There is 3 colored hoses entering the firewall.
Red = Vacumn Supply to the 2wd/4wd switch inside
Green= Normal 2wd, has vacumn all the time to top port on the axel switch slider to keep it unlocked.
Yellow= when the 2wd/4wd switch is moved to 4wd, then the yellow has all the vacumn, it goes to the middle port on the axel switch,when the slider acuates it then passes vacumn to the bottom port, this line leads back to the T-Case where it operates the lockout switch and allows you to shift into 4-lo.
Put it back in 4-Hi and throw the switch back to 2wd and it back to normal.
Theres a lot of other little complicated stuff that goes on but thats the basic way it works and thats where to start with the mighty vac if things dont act like there supposed to.

[Joe Guilbeau]

Well,

Right now I am attmpting to adjust the Range Rod, in the cab, that shifts from 4-Hi to 4-Lo.

She'll go into 4-Low easily enough, but getting her back into 4-Hi...she binds up, and I have to go under and undo the linkage to get the lever to return to the 4-Hi position.

Mode Rod linkage and vacuum have been adjusted to specs and seem to work OK.

My Jeep came from Phoenix originally, from the Carfax Report, how about that?

[scotty]

binding in returning to 4hi sounds more like a bushing prollem than an out of adjustment rod prollem. if its getting all the way into low range the rod is prolly adjusted just fine,so you might wanna give all those little plastic bushings a look smile.gif

does your truck have a body lift?

[Joe Guilbeau]

No body lift, but a 4" Superlift Suspension, and yep, you are correct lots of play in the bushings, and other control rods and arms and linkages.

The dang Range Rod wobbles like a top inside the cab, but we got her as close as we are going to get without replacing some parts.

We fabbed up some rubber bushings from some spare parts stuff and she is shifting pretty well now.

I think that I will rig up a Teleflex Cable for the Front Axle Disconnect (easier tight turns in 4-Lo) and go ahead and rig another Teleflex cable for the Transfer Case.

Should be able to mount a bracket on the transmission hump next to the Range Rod for these two items.

Have to rig up some kind of mechanical interlock to prevent the Transfer from case being shifted into 4-Wheel Drive without the front axles being engaged.

[scotty]

sounds like a cool setup smile.gif