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Chevelleguy 09-21-2003 11:58 AM

10$ NP229 Fix
My viscous coupling was shot so on recommendation from my friend, who owns Texas Auto Gear, I pinned the coupler clutches. The hardest part is getting the t-case on the floor jack while laying under the truck.
-Remove t-case,rear output yoke, rear retainer, rear half of case.
-Slowly remove rear output shaft and retrieve the 15 needle bearings that just fell out.
-Lift the viscous coupling off of the side gear but DO NOT REMOVE THE SIDE GEAR! THERE ARE 202 ROLLERS IN AND AROUND THE GEAR!
-Remove the large snap ring from the v/c and from the other side, remove the small allen screw. Apply compressed air to the hole to separate the v/c.The v/c is full of STP so do this in a drain pan.
-Half of the clutches have 5/16 holes all the way aroud and half only have two. Align the holes that are 180 deg apart with two philips head screwdrivers.
-Use 2 grade8, 2 1/2in. long, 5/16 bolts, w/ the heads and threads cut off, as pins to insert through the aligned holes. You will have to grind them to the proper length inorder to put the cover back on the v/c.
-Before putting the v/c back together, remove the rubber seal so that ATF can lubricate the plates against the case.
-Reassemble the t-case with silicone, use bearing grease to hold the needle bearings in place, and put it back in the truck.
-You now have a working 4WD hi range. You can't drive on hard pack in 4wd now,but a new v/c is about 400$. Fair trade off if you ask me.
Total out of pocket?
2-5/16 bolts=1.02
3-qt ATF=5.00

timmirvin 09-21-2003 04:07 PM

So....did I miss something or did you just install a "Part Time Kit" in your 229??? :D :D

And don't have to worry about the VC ever again....

scotty 09-22-2003 01:26 AM

great fix if its good enuff shape to do that. 2 of the 3 that ive messed with the v/c was split open along the front seam :eek:

while youve got it apart,you may consider removing the interlock pill that keeps you front using low range in 2wd ;)

Bob Barry 09-22-2003 01:34 AM

Cool Tech!

Now, if I could just find a source for the proper silicone fluid (think it's different from the fan-clutch stuff?), I could do a writeup on rebuilding that $350 VC unit...

Wasn't somebody here working at New Venture (New Process)???

Chevelleguy 09-25-2003 12:45 PM

Thanks for the comments. I'm very pleased with the results.

diver 11-01-2003 04:41 AM

Could someone with a bit more knowledge explain this to me? Would this make it as stong as a 208? And what is this interlock pill? How would the shifting to 4wd hi, 4 wd lo be achieved and if you took the pill out how would 2wd low be achieved? Id rather spend $10 and keep my driveshaft until I can afford and atlas than buy a 208, but I still want to wheel. Thanks.


Joe Guilbeau 11-02-2003 04:38 AM

The NP229 Transfer cases have what is called a Viscous Coupler inside them that acts as a Torque Converter so as to allow the front and rear driveshafts to not bind up (as when turning a corner in 4-LO).

Those of us with the old Borg-Warner 1339 Tansfer Cases and the Low-Range reduction unit options can all recall the chirping of tires on pavement due to the fact that all four wheels in 4-Lo were locked together with the driveline.

This means that cranking over the steering wheel in 4-Lo and applying the gas....something has to give. The outer tires and the front and rear axles all travel different radius's around the turn.

In the case of the NP229, the Viscous Coupler is a silicon filled resevoir with "shearing plates".

When the vehicle is placed in 2-Hi, the front driveshaft is disconnected from the transfer case driveline and more specifically the left drivers side of the axle is dosconnected via a coupler operated by the vacuum shift motor mounted on the Drivers side front axle (in my caase), while the right side axle is always connected through the differential housing and gearing to the driveshaft.

For the Left Front Axle, a coupling sleeve slipped over something in the housing, which locked the driveshaft in one side of the axle to the coupling gears that drive it.

This is why, on some vehicles, it is wise to come to a slow crawl in order to shift into 4-lo from 4-Hi. This locks the front driveshafts together, and allows the torque from the front driveshaft to be sent equally to each front wheel.

Meanwhile, in the transfer case, in 4-Hi the rear driveshaft continues to be directly connected to the transmission through the transfer case (as it is in 2 Wheel Hi) but now, the viscous coupler is trying to maintain the same rotational rpm's between the front and rear dirveshafts.

It attempts to do this because, as the difference in driveshaft rmp's increases (betweeen the front and rear driveshafts) the fluid (Silicone) inside the viscous coupler heats up, and thickens and provides more shearing force between the plates.

Sort of a liquid clutch pack, if you will, between the front and rear driveshafts.

Now, i have skipped entirely over the Limited Slip Differentials, Open Differentials, and Trac-Loc Differentials cause I stupid in these areas.

On my 1983 Cherokee Chief with the NP229 and front Dana 44 Vacuum operated Axle shift motor, the above description holds. There is another Vacuum operated shift motor that activates a shift rod to place the Transfer Case into and out of 4-Wheel Hi drive into 2-Wheel Hi drive and vice-versa.

I will let other more technically versed individuals make the significant additions to the rest of the operation.

In my opinion, this is a very nice option for a street rig, that is taken occasionally off-road.

The following is from Scotty, in Dayton OH and explains much better that I ever could about the operation...(Thanks! Scotty!!!)

"...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...

diver 11-02-2003 04:44 AM

I appreciate the response but will the $10 fix work? lol and how would it the tc shift then and scotty mentioned removing the interlock pill? what is that and how do you do it and how does it then shift to 2 wheel low?

Joe Guilbeau 11-02-2003 06:04 AM


Originally posted by diver:
I appreciate the response but will the $10 fix work? lol and how would it the tc shift then and scotty mentioned removing the interlock pill? what is that and how do you do it and how does it then shift to 2 wheel low?

You are asking why modification of the stock unit will work. I am the wrong guy, the modifier would be a better person to answer this question.

The transfer case shifts via the vacuum shift motor on the Mode Control Rod on the NP229 case.

In the case of chevelleguy, his NP229 Viscous Coupler was "shot" so attempting to place the vehicle in 4-Wheel Hi was problematic, as the Viscous Coupler inside of the NP229 Transfer Case no longer contained the Silicon fluid to act as the "liquid clutch" in order to apply power to BOTH front and rear driveshafts at the same time.

So, he essentially bolted the plates together, so that they always transfer torque from the transmission to both the front and rear dirveshafts at the same time. Therefore there is no longer any possible way to put it in 2-Wheel drive with this particular modification. However it probably does not matter much, as long as you keep the front left axle disconnected via a shift motor (not all vehicles have this "Feature"), then you essentially have 4-Wheel Hi set.

Inside of the Transfer Case there is some sort of interlock, Scotty is better informed on this subject than I am.

Again, it hardly matters, as the plates inside the transfer case have been bolted together, they have essantially put the vehicle in all wheel drive.

Only those applications where the front left axle is disconnected from the front differential need to be concerned (I think!) about the interlock inside the transfer case.

Something about being able to drive at 75 MPH in 4-Wheel Lo or something to that affect.

Murphey seez...If it ain't broke, you can't fix it

Chevelleguy 02-05-2004 03:41 PM

Sorry to bring up this old thread, I was off line for a few months, but Joe is incorrect on one point. The only thing this modification does is eliminate the ability of the VC to slip in 4HI. It has no affect on 2WD. That is controlled with the mode fork in the case and it still works.

scotty 02-06-2004 12:14 AM

id forgotten about this thread as well :eek:

diver,to answer your question:
the interlock pill prevents the planetary gears in the front of the case from being shifted into low range while the case in 2WD. removing the pill will let you shift it. [img]smile.gif[/img] its as simple as pulling up on the H/N/L lever with the vaccum dash switch in 2wd [img]smile.gif[/img]

i have not personally performed this modification,so i cant personally comment on how hard it is to remove the interlock. another board member told us on another thread that it was possible.i can comment on the fact that there are indeed a bunch of needle bearings that will fall out when you remove the viscuous coupling,as chevelleguy said,and this does make reassembly alottle tricky. you needf to stand the case straight up,and use vaseline or grease to hold the needles in plase while you reassemble.

while this mod does add some reliability to a 229 that doesnt need full time 4x for street use,i dont think id go so far as to say that this makes it as storng as the 208. the v/c is still part of the equation,with the 2 piece output shaft,and all the little needles,the innards of the 229 are much more complex. part of the 208s strength is its extreme simplicity [img]smile.gif[/img]

as i mentioned,its not uncommon for the v/c to split. silvery looking fluid is an indicator that your v/c has split and puked out all its magic siklicone fluid.not sure if pining the clutches makes it any less likely to split the coupler open,hopefully so,as this sounds to me like a great mod for a v/c thats in goof enuff shape to pin the clutches

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