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How to: Manual 233

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A few members wanted information on how I made my np233 shift manually so I will try to give a few details about what i did and why. fyi i have a 2001 ex cab zr2 pickup a/t. There are a few options along the way but my mods totalled 22 dollars and about 4 hours in my driveway.

Since I have owned my truck (4 years and before that i owned a reg cab s10 4x4 with same system) i have had more problems with the 4x4 system than anything else. It is quite common for any number of the stock 4x4 components to fail in time, whether its a $200 shift motor, a $400 tccm , a leaky transfer case vacuum switch (which can also kill hvac systems and front diffs) or a faulty dash switch. I just wanted to eliminate all of this to make my 4x4 system as cheap, reliable and simple as possible. the only special tools i used were a dremel, a circular saw with metal cutting blade or an angle grinder, and a small welder. u can probably do without a welder and find another way to fasten parts.

There are a few ways u can set it up:


1) remove only the electronics - this means removing the transfer case shift motor. this will render all electonics in the 4x4 system useless. neither the tccm or the dash switch will function or have a pupose (sold mine on ebay once i was sure the mod was permanent). you will have to cut a slit apox 7"x3/8" in your floor and install a lever to shift the transfer case. if u put it where i did then u will not be able to see this when completed and it keeps a very stock look. the switch on the t case will still opperate as normal to engage the front diff.


2) eliminate t case vacuum switch - this can be done by itself leaving the tcase to be controlled by the dash switch or in combination with the electronics removal. you could use a posi lock type setup or simply buy or find a self venting vacuum solenoid to actuate the front diff. i got my switch from the AIR system so i didnt have to buy one. this is hooked to any electrical toggle switch to engage and dissengage the front diff independently from the t case. this means while the t case is in 4wd you can have a system similar to the auto-trac system except you control the diff instead of the computer. can also put the tcase in low range and not engage the front diff effectively giving you 2lo. didnt think this would be useful but it helped alot a few weeks ago backing a heavy trailor full of firewood up a steep driveway with sharp turns.


Before u start tearing into your truck let me say this...i have driven 10,000 miles with my 4x4 this way and have had no bad effects. THAT DOESNT MEAN NOTHING WILL GO WRONG WITH YOURS! If you attempt this do so at your own risk!!!!!!! I will not be responsible for any damages that might result from the modification of anyones 4x4 system!

I will attempt to cover the areas where potential problems could arise as we go.


The np 233 transfer case is used with the 3 BUTTON electronic 4x4. This DOES NOT apply to models with auto track 4x4. The 233 is pretty much the same as the earlier manually shifted np231. Same case and most of the same internals. the main difference is that 233s only have 3 positions 2hi 4hi 4lo there is no neutral position. The 233 is also harder to shift because it was intended to be used with the electric motor which is geared down and actually applies a pretty high amount of torque. For this reason it would be very hard to shift this tcase with any linkage or cable assemblies like those used on most manually shifted tcases. there is a detent bolt that actually loosens the tension on the shifter but I would definately recomend NOT messing with this. but not to worry because the tcase in my z just happens to be right where it needs to be to make a straight rigid shifter come up right between my center console and my seat! a lever like this would be more than long enough to apply the leverage needed to effortlessly shift the stiff 233. which brings me to my first warning. SHIFT CAREFULLY !! THE SHIFTER WILL BE SO LONG ITS HAVING A BREAKER BAR ON YOUR TCASE. feel your tcase out and never force it. you could easily snap something in your tcase with too much force.


GETTING STARTED- Figure out what you want to use for a shifter. i would recommend getting the shifter designed before cutting holes in your floor. the shape of your shifter will determine exactly where u need to cut. (Note your design may vary depending on what console and seats u have.) i used 2 5/8" combination wrenches jointed in the middle by a 5/8" allen bit. this allows the top piece of the shifter to move left and right in relation to the bottom one. the reason i did this is because when the lever is in 2 hi (all the way to the rear) it needs to be close to the center console in order for it to fit between the seat and the console. however when in 4 lo (all the way to the front) the shifter would hit the console (which bulges out forward of drink holders) before it reaches its full forward position. so the joint allows the top half of shifter to slide left when in 4lo to clear center console. another benefeit of the slider is that u can take it out and adjust the angle anytime you want, and this is the only way i can remove it from the vehicle because the other end has a big wad of metal on it which will not come through the slit in my floor. i just cut a groove with the dremell all the way around one end of the allen bit about 1/8" from the end to accomodate a removable e clip. i welded the open end of one of the wrenches to the other end of this bit. it ended up like this:






That will make the smooth end of the wrench your shift handle. You could probably find a wrench that would fit directly on the tcase. it is a round shaft with 2 flat sides. i beleive a 9/16" wrench fits well but the problem i had with that is 2 9/16" wrenches werent quite as long as i wanted. so i decided to use 5/8" wrences which were a little longer. i dissasembled my tcase shift motor and removed the piece that fits onto the t case it has gear teeth on the side and i just welded the OPEN END of the wrench to the fitting (the closed end needs to be on top for the allen to slide through)





if u choose to do this i would get the rest of the shifter made and the floor cut before i actually welded them so u can get the angle at which u attatch the two more precice. thats the other reason i didnt put a wrench directly on the tcase, there are only 2 angles a wrench can point and nither one were perfect. i would not dissasemble the shift motor unless u want to use this part. or unless urs doesnt work anyway and/or know u wont want to use it again. alternatively you might be able to cut a short piece of 9/16" wrench and weld that onto the rest of your shifter at any angle u want. now that u have your shifter worked out its time to tear stuff appart!!

First put your truck in 2hi and then unhook your battery. get under your truck and get familliar with the area around your t case. NOTE: Refer to the "how to replace t case shift motor" thread for complete instructions and pictures. I am writing this up after the install and got no pics of the t case area before i put my skid plate back on.

Undo the 8mm bolt holding the shift motor wiring harness to the shift motor. unplugg and bend it somewhere out of the way.

Next you will want to remove front driveshaft. i have heard that u can remove the shift motor without removing the driveshaft but i dont know how. go ahead and remove the 4 bolts on the front u joint drop the front of shaft and tap the entire shaft forward from the rear of shaft with a block of wood and hammer till it starts to slide forward. tape the front u joint together with electrical tape and slide it forward and out of the way. it only takes a couple of min.

Remove the 3 bolts holding the shift motor to the t case, then remove motor. note the position of the shaft coming out of the tcase. this is 2hi position. from there it turns counter clockwise one click to the 4hi position then 1 more click counter colockwise to the 4 lo position. u should get under your truck with tires chocked, trans in neutral, and try to manually shift the tcase with a wrench at this point to confirm it works properly ESPECIALLY if u have had previous problems with your 4x4. it should be stiff but not rough. dont force it though. if everything seems cool then make alot of meaurements to figure out where to cut your floor.

Remove the driver seat and center console. this sounds like alot of work but takes 10 min or less. there are 3 nuts and a t-45 torx bolt holing the seat in. make sure you disconnect the seat belt sensor before ripping seat out. there are 4 10mm nuts holdong the console in, 2 in the rear interior of console and 2 under the tray below cassete player. slide console out a little then disconnect cassette player harness if equipped.

Now you will need to cut and/or peel back carpet. i made my cuts under the console and seat area so they wont be visible. now that u have bare metal exposed its about time to cut it.






I used the front right seat stud as a reference point because it is visible from under the truck as well as in the cab. from the center of this stud i found a point aprox. 1" to the rear and approx 3 1/4" to the pass side of the stud. this is the appoximate center of my cut and is directly above the shaft on the t case. YOUR MEASUREMENTS WILL VARY!!! i started in the middle of the cut using an ordinary circular saw with a metal cutting abraisive blade. ALWAYS KNOW WHATS UNDERNEATH YOUR CUT! FUEL LINES RUN BELOW! DO NOT USE A TORCH. i made a small cut first then got under the truck and looked up to check the alignment of the cut with the t case. adjust the cut as necasarry while u go. u want to get the two as paralell as possible. once i got a small cut started i worked my way to the rear a little at a time making my cut just wide enough for a wrench to fit through and have a little play. i mocked up my shifter occasionally and kept cutting a little at a time untill just before the shifter hits the tcase. at this time i marked and welded the fitting onto the wrench at the appropriate angle. this is as far back as the shifter can go. this will be the possition of the shifter in 2hi. now start the forward part of the cut going just far enough to get clicked into 4 lo when the shifter is all the way forward. make sure u keep checking to see if the cut is straight so u dont end up with a shifter that binds in a crooked cut or one that isnt parallel with the t case. i tried to leave my cut short enough so that it fully engages in both 2hi an 4lo yet the shifter itself actually rests on the truck body to keep vibration down and also to make it impossible to shift too far. once u are done with your cut remove the shifter and lay carpet back in its original possition. make 1 cut exactly where u cut the floor. the carpet makes a seal that is partially weather tight and barely visible when complete. ive been mudding a few times and nothing has got in the cab but its possible. that area has a skid plate. climb under truck.

U will now have to find a way to keep the shifter on the shaft. i simply drilled through one side of the shaft and installed a cotter pin.







Once the bottom part of shifter is installed and u confirm that u can shift through all ranges with no binding then go back to cab and install the rest of the shifter and slider. if everything works then put the seat and console in and make sure it fits.


4 lo position...





4 hi position...




2 hi...





if u plan to dissconnect your t case vac switch also then now would be a good time. there are 3 lines going to the switch which is just above where the shift motor was on the top of the t case. 2 of these lines are the same diameter and one is slightly larger. the larger one is a vent, the smaller 2 are the vacuum lines. remove the smaller vac lines and cap the two nipples onthe switch with rubber caps. leave the larger line attatched to the switch and leave the switch on the case. all 3 of these lines cross over the top of t case and tranny to the passenger side and the forward towards the engine and up along the firewall coming out behind the distributor. they are taped together a few places. cut tape and ull the 2 vac lines up from the engine bay. on mine there was one PITA wad of tape right behind the distrubutor. its tight in there and i almost couldnt reach it. gm used some sort of super tape that will not tear. once u get the two lines into the engine bay sat them aside. one is the supply line from the intake, the other goes to the vacuum actuator under the batt. AFTER U ARE DONE AROUND THE TCASE HOOK THE FRONT DRIVESHAFT BACK UP

If u want to controll your front diff with a switch then u will need a vacuum solenoid. i got my original from my own truck. i removed the entire AIR pump and all accesories a couple of years ago because the system caught fire while towing. im lucky i had a big pepsi to put the fire out or the z wouldnt be here. rather than have gm replace all of this under waranty i told them i would take care of it, which i did by removing it all. i didnt want new parts that were just gonna catch fire again. at the time the truck only had 23,000 unmodified miles. there is a vac solenoid in that system located by the AIR pump behind pass side of front bumper. if u dont want to sacrivice this or if u have no AIR system then go to the dealership and ask for a vacuum solenoid from any make or model, the cheapest one will do fine. as long as it has 2 places to put vac tubes, 2 wires, and switches the vacuum ON to something when it gets 12 volts. I got one that is for some accesory on a 2500 diesel for my friends truck for about 25 bucks it works fine too.

Once you have a solenoid its an easy hookup. put the supply vac line from your intake on the solenoid then hook the solenoid up to 12v through any toggle switch. i put my front axle switch here:




rear flood light, front fog light, and front diff switches. crank vehicle and make sure that when 12v is applied to the solenoid that u have vacuum on the out side of the solenoid and when u take the voltage away then the vacuum also goes away. if all is good then attatch the vac line going to the actuator under the battery to the other plug on the solenoid. i didnt even mount my solenoid its just laying there by my ecm.





i figure if it ever fails i can always unhook it and connect the two vac lines directly in an emergency. its super easy to get to.

if u want to get rid of the vac completely then get a posi lock cable.

well i guess thats about it. try it out easily at first till u get used to it. u may notice vibration in the drivers seat because the shifter touches it but thats the only undesirable effect ive had. the same rules apply for shifting as always...neutral to go into or come out of low range it helps to be rollin a little bit. u can shift into 4 hi from 2 hi just about any time. just move the lever and hit the switch. you can also drive around with the tcase in 4hi position and just hit the diff switch when u hit a slick spot. it engages quickly. and is similar to having auto 4wd. the other thing is an indicator light. there is a switch on the front diff that is supposed to tell the tccm when the front axle is engaged. this can be hooked to an indicator light so u can see exactly when your diff actually kicks in. im sure i left a few things out somwhere but i will try to answer any questions that anyone has. i have used it many times and like it much better than the stock configuration.



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I read it all and it's a good dingin' write up.


Now, I'm hoping this board database is being backed up regularly becuase we're getting some good write ups that I haven't saved to my computer - yet.

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Just excellent. This is one of the best write-ups I have seen on a Z and has potential to save someone hundreds of dollars!!!! icon_appl.gif

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good stuff, stroker! i actually thought that this was already a write up that had been stickied. it def. should be Stickied!

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Now that you don't use the 4x buttons on the dash.....


I was thinking what someone could use those for.

How about offroad lights?


2HI could be for those two lights on the bumper.

4Hi could be for forward mounted roof lights

4Lo could be for any reverse aimed lights.


Would be easy to remember which is which that way.... and keeps a stock appearance. Plus, other locations remain available for different switches.

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So I figured I'd write a big thanks on this writeup wouldn't have 4hi without it mine didn't completely require the 2nd wrench it was also to close to the seat and gets buried in the carpet in 4 lo so I guess results may slightly vary but all in all it works great thanks

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very nice mod! i've thought to do that but i dont knew if it works fine and now i see it works!! :)



and now a have only one question... when you remove the encoder motor from the transfer case, the shaft on it dont leaks some oil????


i realy want to do this modification for my truck...

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Is this something i could do with my 4WD? ..cause i have Auto4WD too? hmm?



who else on this site has done this mod ? ? ?

Edited by nmetankzr2

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Is this something i could do with my 4WD? ..cause i have Auto4WD too? hmm?



who else on this site has done this mod ? ? ?


No this will not work on the 236. The front output shaft is controlled by some kind of clutch assembly. Without the electronics the front clutch assembly will not engage and you will only have 2wd 2hi and 2lo available to you. I went through this right before swapping in a np231 out of a 96blazer.

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Now that I've mostly finished my manual conversion I'll add some input to this as well.


I went about doing this in a completely different fashion when first started working on this, since in theory by converting the original T-case motor/encoder motor I would be able to keep everything functioning as if it had came from the factory that way.


The plan was to manually shift my NP233 t-case by using the t-case motors housing (including its internal gears) to shift the t-case, to do this i had to machine a new shaft housing, bushing, shaft, and lever to shift it (lever for the t-case shifter cable to connect to).


More info on this is in my build thread starting here on post #62


It in action

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nice write up stroker.. i went about it a little differently with a linkage setup rather than cutting such a large hole in the floorboard.. by going with a linkage setup i was able to place the pivot points in positions that give me leverage without having a large shift arm in my cab.. not trying to step on toes here.. :LS1MikesTruck:




1) start off by placing the truck in 2wd (and neutral, make sure to block the tires to prevent rolling). pull off the front drive shaft and then the electronic shift assembly. mark out the shaft where it needs to be for 2wd.

2) replace the electronic shift assembly, place the truck in 4 HI. then again remove the assembly and mark for 4 HI

3) replace the electronic shift assembly, place the truck in 4 LO. then remove the assembly for the last time and mark for 4 LO




4) temporarily take apart the electronic shift assembly and mark the alignment of all internal gears so it can be put back together EXACTLY how it was. (i plan on selling this assembly so i made a different piece to attach to the t-case.) if you have no reason to keep the assembly (ie the shift motor is out or it is stripped) go with what stroker did and save the time...


locate the final gear that physically places the t-case into gear. (be sure to mark this gear) then remove the gear and start off by taking measurements. i used a thick washer and 2 pieces of square stock to reconstruct the desired shape. Be sure to test fit after every change! Place the washer alone on the shaft to ensure it fits snug, as well as after each piece of stock is tacked into place.... After you have both pieces in the right place, finish both welds all along the outsides of the stock.






5) Create a leverage arm as long as you can without hitting body and attach it to the piece you just made. (Be sure it is not going to hit either body or fuel lines shifting from gear to gear. Try it out before final welding. ) i have a 3" body lift making this part a lot easier... without a body lift you will not have as much room for a long arm, giving you less leverage on the t-case.


As a retainer to keep the arm tight on the t-case i simply tack welded another washer onto the shaft. drilling a hole and pinning like stroker did is probably a better choice, i just don't have the patience. touche this shaft is hard..




6) find a location that you feel comfortable with having your shift lever. drill a small pilot hole from inside the cab to locate exactly where you are under the cab (make sure not to hit fuel lines). be sure there is a clear path between your location and the physical shift arm you just added on your t-case.



7) Either peel back your carpet or cut an X into the carpet at the desired location, your preference. after i cut the carpet i peeled back the created corners and temporarily tacked them out of the way with four 1/4" screws. drill a hole the size needed to fit the media you choose to connect the inside shift lever to the lever under your cab. ( i will be using a 1/2" thick grade 8 bolt to ensure i dont twist it off)




8) Cover all insulation and carpet with water soaked rags to avoid setting fire to your precious Z. use a piece of either square or round tubing that fits your media snug as a base for your shift lever. (as you can see i used square tubing. excuse the nasty welds, i was out of gas and later fixed them)




9) Now create your shift lever. (For my shift lever i used 1" strap that is 1/8" thick. Drilled a few holes to make it more presentable and painted it.) weld on the shaft you intend to use to connect your shift lever to the linkage under your cab. ( this is when i welded the bolt to my lever)






10) At this point test fit the shift lever you created to ensure you can shift without running into the center council or getting in the way of your gas pedal. you may need to adjust the shift lever base (square or round tubing) to get the angle correct. this step will irritate you and take a while because this is what you will be looking at from now on..


11) create the shift arm under your cab. this arm will connect the arm you created on the t-case with your shift lever. for leverage purposes this arm doesnt need to be very long, the closer to the pivot point you are the better the leverage will be. ( make sure you have a long enough lever to get through all 3 gears )DO NOT FINAL WELD YET.



12) If you go with the same leverage scheme i did, the farthest forward position on your shift lever in the cab will be 2HI. Thus the farthest back is 4 LO. Position your shift arm in the cab to the 4LO position as well as making sure the t-case is in 4LO ( i put a marker under the shift lever to make sure the lever did not hit the floor before i got into 4LO )



13) place the under body shift arm in place and weld in making sure that 4LO is the far back position and the 2 HI position is the far forward on your shift lever.


14) create your linkage. For linkage i used two 5/8" rod ends, two 5/8" bolts, two 5/8" lock nuts, and some 1/2" steel rod. ( i avoided using threaded rod or ready rod because it is weak and will not have the strength needed to push back through the gears, again your call)




15) Bolt in your linkage and try it out. At this point you are done and all you need to do is make sure it works without binding.




here are some images of my shift lever.












Edited by bmfastrabbit

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surprised there arent any questions yet..


if anyone by chance has the internal shift arm for a 231, i want it.. then i can thread a nut on..

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Has anyone done this mod with a manual trannsmition?

What did you do with the electronic switch panel on the dash? is it there just for show now?


you could use the block off plate from a 2wd s series

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