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How To: Swap in a NP241 transfer case

22868 Views 20 Replies 8 Participants Last post by  wrenching76
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A 355nation How To presented by

Project Name
Project manual tcase

Project Description
Install a Np241 manual transfer case in place of the stock one

Skill Level

Project Vehicle
Make: Chevrolet
Model: Colorado
Year: 2006
Engine: 3.5L
Power windows: No
Sun Roof: No

Tools Needed
  • Miscellaneous sockets
  • 2 swivels
  • 15mm wrench
  • 9/16" wrench
  • Hammer
  • Pry Bar

Project Time
2-4 hours

Project Cost
  • 3 quarts of your preferred ATF
  • Price of np241 transfer case
  • Price of custom front driveshaft or adapter
  • Price of custom rear driveshaft (Tom Woods) $300
  • Price of new output and input seals
  • Price of new custom shifter
  • Price of newer 4l60e to np241 adapter (part#15005474) I got mine off ebay for
  • Permatex Sealant

I'm doing this swap because during my last offroading adventure the lights on my dash went out and I'm tired of the electronic crap on our transfer cases. I picked up the transfer case off craigslist for $200. It has to be from a 1990-1991 full size Blazer or Suburban. The 1989 is a mechanical speedometer, the '90-'91 has the Vehicle Speed Sensors (VSS). I went ahead and changed both output seals and the input seal. With this swap you will need to run a custom front and rear driveshaft. The front output will now be a 1/2 ton chevy pattern. The transmission crossmember will have to be altered as well. The rear slip yoke from a np241, np205, or np208 from my research will work. I'm reusing my front driveshaft since I had an adapter for my SAS to adapt our transfer case to a 1/2 ton bolt pattern and I ordered the rear from Tom Woods for $300 shipped. You will need to fab up your own shifter. I ordered a single stick from offroad designs.

  1. Unbolt the rear u joint from the differential and then slide the drive shaft out of the transfer case. Have a drip pan or rag because you will have some gear oil come out.

  2. Unbolt the front driveshaft from the front differential. Then unbolt the flange at the transfer case. You may need to give it some love to get it to come loose.

  3. Unclip all the electrical connections off the transfer case and move them out of the way. The only one that will be reused is the VSS wiring. The 2 wire harness that is purple and yellow.

  4. Unbolt the 5 bolts that holds the transfer case to the transmission and slide it away from the transmission. You can use a transmission jack to remove it. I did it the old fashion way and did it manually. I don't recommend it unless you have help.

    That is what you'll be left with. It shows you where the 5 bolts are located.

  5. Place a jack underneath the transmission and put slight pressure on it. You will need to remove the 2 bolts that mount the adapter to the crossmember. Theyre on both sides of the mount.

  6. You need to support the transmission off the crossmember and remove one side of the crossmember. I removed the passenger side 2 bolts completely, then the cross bolt on both sides, lastly loosened up the driver side 2 bolts just to give it some give to drop down. You may need to use a pry bar to get it to slide down. Sorry I don't have a picture of this because I was slightly nasty at this point.

  7. (You will need a drain pan for this step) Since our adapter is for a 5 bolt transfer case our stock adapter will not work. You must get the one specified above. If you cant find it on ebay, you can go to the dealer and get one from a 97-99 Silverado with a 4l60e to np241 transfer case adapter.

    I suggest starting from the top. Lower the transmission down until it wont go anymore. Remove the top 2 bolts of the adapter. Then jack the transmission back up and remove the remaining 4 bolts. Have the adapter there and ready. You will loose some transmission fluid or at least I did. Once you remove the last 4 bolts pull the adapter off and put the one from the Silverado in its place. Reassemble in the opposite order and reinstall your crossmember.

  8. Loosen the transmission mount via the 2 nuts inside the crossmember opening. You don't have to remove them completely. Then align the 2 holes in the top of the mount with the 2 mounting holes on the adapter. It uses the same bolts that our stock mount uses. Once they are tight, re-tighten the 2 nuts inside the crossmember.

  9. Install the transfer case onto the transmission. I went ahead and put 3.5 quarts of ATF in prior to installing, then i pulled the fill plug and let the excess drain out. I also permatexed the mating surface. I had my father help me lift it up and side it in. It's slightly bigger than the stock transfer case so it has to go up sideways, then turn and slide the input shaft onto the output of the transmission. I ran all the bolts in by hand first. You will have to have 6 new bolts as before there were only 5 and they are also the wrong bolt. My transfer case came with the correct bolts. If yours doesn't a simple call to the dealer will get you the right ones. I used a boxed in 9/16" on the bottom 2 bolts. The top bolt is where it gets interesting and you have to be creative. I used a long extension with 2 swivels and a short socket to get it tight. That is your end result.

  10. Reinstall your front and rear driveshafts as they were removed.

  11. For the wiring of the vss. First verify that your sensor is in good working order. To do this I just put the truck in drive without a driveshaft and checked AC voltage across both wires. I then matched purple to purple, and yellow to green. I verified it works with my gps. Once you get the shifter of your choice installed you are now worry free about if you get a little too deep in the water if your 4x4 module is going to fail. Or any other bugs that arise with our stock transfer cases.

    Now to the shifter install. I ordered a floor shifter from offroad designs. It's not for a np241 but we adapted it to work.
  12. We took and cut the handle off. Then shortened it 7" and cut the last 2 holes off. We also put around a 45* bend in it.

  13. We then used an air dremel to cut a small hole enough to get the shifter through. We then cut away to where we could make it fit. We then drilled holes to mount the shifter. Had to massage the floor a little. We also trimmed a corner of the mount off that wasn't going to be touching anything. We trimmed 1 1/4" off the all thread to make it all work. The all thread is almost maxed inside the joints so if it needs adjusted we could just trim a little more off. We then cycled the shifter making sure everything cleared and worked properly.

  14. We chose to pull the passenger side seat out and lay the carpet back. Once we got everything bolted together we laid the carpet back over. Trimmed a hole for the shifter to come through the carpet. Then slowly made the hole bigger til it looked good. Reinstall the seat and have fun.

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I just figured someone else may benefit from this. It cost me maybe $650 to do this swap. But I didn't need a front driveshaft. I did replace the vss sensor and put the 4lo switch in. It hasn't been wired up but my trans still shifts. I'd say most could get the proper slip yoke and run a mismatched ujoint and retain their rear driveshaft.
One question. If you didn't have the h3 floor shifter would you have been able to run the 241 shifter on top of the tunnel?
Maybe with a 3" body lift but it still probably wouldn't. Where it is tho isn't real bad. The seat clears it in every position.
Oh ok. I looked at the pics again. I see how the shift linkage is on the pass side of the t-case.
That shifter is just a single stick from offroad designs. You may be able to make a different one work up closer.
I know this thread is a bit old but is this transfer case MSOF (Mechanical Shift On the Fly)? or do you have to stop every time you want to change it?
As long as my hubs are in yea. You can shift 2-4hi on the fly. It's not really old. It just got published this month. Took a while to get it all pieced together.
As long as my hubs are in yea. You can shift 2-4hi on the fly. It's not really old. It just got published this month. Took a while to get it all pieced together.
So you're saying if your hubs are engaged the you can just shift from 2 to 4hi while cruising?
Yep. Just like a 4x4 colorado. Now if my hubs were unlocked I couldn't. It would definately fuck shit up then.
This is awesome. I wish it were possible to put the shifter in a location that looked a little bit more... "stock" but there isn't really a place in this truck to make it look like a Silverado would.
One question though, is there a difference in T-Case gearing between the two models?
I think the np241 is like .1 lower in low range. You'll never know the difference. This was done to get rid of the electronic crap. It's also a good way for 2wd guys to sas. The only difference in the 2wd and 4wd trans is the rear adapter that you have to remove.
Getting rid of the electronics is the main reason i want to get rid of it. I cringe everytime I hear those actuators wondering if that's gonna be the last time I hear them banging around before I'm sticking limping I'm 4wd or going nowhere at all.
If you have tools I've been told you can pull the actuator and shift it manually if you get stuck in like 4lo. But I've never had to.
I'm seriously starting to wish I could sas and swap to this tcase Kuz I am sick of my 4x4 not working maybe soa, also wonder if this would work with my 5 speed
I don't know. Next time I'm in Florida I'll sit a 4l60e and the 5speed side by side and measure the pattern. I'd say it'd have to. Unless gm made 2 different adapters to bolt out tcase up. Only difference in the 2wd and 4wd on the autos is the rear housing which are interchangeable to 2wd and 4. So ima say the 5speed is the same pattern for the adapter to bolt up the tcase unless there's 2 different.
hey gway…. question for yah. how did you get 4low signal to work so trans will shift in 4 low? any help would be good. thanks
I actually haven’t wired the switch up still. There’s a 4lo switch on the tcase. You can wire it to the harness that goes to the wiring for the 4wd module. I was also told by a guy who’s good with wiring that you can just ground that wire whenever you shift into 4low and it does the same thing. I don’t remember which wires to wire up. Would have to look through my messages. It will shift. You just have to get the rpm’s up lol.
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