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Discussion Starter · #1 ·
I have a '99 7.4L K2500 Burb with an auto-trac np246 that has failed.
I picked up a np241 that I'm going to use in it's place. I'm looking for info on wiring the 241 vss to the 246 vss harness.
It looks like the 246 has two sensors at the rear and one for the auto-trac.
Does anyone have first hand knowledge on what wires from the 256 I need to splice to the two wires coming from the 241.
Thanks for any help.

Aaron
 

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When i did mine i used the rear most VSS. The 241 has three wires coming off the shift lever. one of the outside wires needs to be grounded. The other outside wire needs to be ran to the front diff for an actuator signal. The middle left alone or run to the floor shift lever. Its been a while since i did this. Ill crawl under my Tahoe if you need more specific info. The large harness going to the 246 pretty much gets cut off.
 

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Discussion Starter · #3 ·
Thanks for the info . I found an old post that had the info. The green and purple wires hook up to the 241 vss. I test drove it and it worked fine.
The 241 came out of a early 90's GM and has a 2 wire indicator instead of the 3.
I still have to get the driveshaft. It has a companion flange instead of a end yoke of the front output. I'll need to find a driveshaft that is a direct replacement or a flanged yoke and build my own.
 

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The 246's aren't as bad to fix financially as they used to. If you really want to get away from the 246, then the only simple option is the mechanically shifted 241. You will need a front driveshaft from a 95 and newer to clear the neutral safety switch. You will also need a shifter and linkage. Make sure to get one with the same input spline count. There are different input gears for the 4l60E and the 4L80/Manual.

A 261 would be an option, but you would still have the same crappy magnesium case. The front driveshaft would be reusable with this swap.

If you ever need parts to fix t-cases, be it new or used, let me know.
 

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241 = linkage shifted
243 = electrically shifted
246 = viscous coupling electrically shifted
 

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Discussion Starter · #7 ·
Got around to getting a front drive shaft(good thing I have other 4x4's) thought I would bring back this old thread to keep all the info in one spot.
I'm trying to figure how to engage my front diff, so I cab use 4 wheel drive.
I would like to use the buttons in the truck. Anyone change out their NP243 or NP246 for a NP241 and figure out the fornt axle actuator?
Thanks for any help
Aaron.
 

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Discussion Starter · #9 · (Edited)
guidolyons thanks for the info. I may do this if mine quits working but in the meantime I need to get this hooked up. It's been unused for the last year so it may have crapped out.
I'm going to try and chase the wires out and figure it out tomorrow. I'll post up what I find out and how I(f) I fixed it.
 

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Bringing this one back from the past to ask some questions and correct some confusion the best I can. I have an '01 ECSB z71 4L60E. I used a np241 out of a '91 light duty k2500 and the driveshaft from it as well. So for all of you who have the driveshaft out of a pre '95, it WILL work. It was a 700r4 truck so the installation was straight forward and easy. Everything went in perfect except the front driveshaft was about 3/4in too long. So I took the driveshaft apart (It slides apart) and used a chop saw to cut 3/4in off of the splines. Then I cleaned up the splines the best i could with a metal file and then greased it (be careful to not put too much grease on it or it won't compress all the way and will seem to still be too long.) I got it in the truck and got the u joint straps tight and everything. The VSS was pretty straight forward as well. Just cut the 241's vss and wire it in to where the 246's goes, matching up the wires colors. Now, what DOESN'T work. This is where I have my questions. I've read every post on google I could find about 246 to 241 swaps and multiple times they have said that you ground one of the outside wires on the 241's wiring harness and send the other to the black/grey wire on the front actuator. So, I assume that the way this works is that the 241 has just a basic switch in it that completes the circuit and grounds the wire that goes to the front diff. So i just grounded the black/grey wire on the front diff with a switch (so i could have 2lo when i wanted) but it didn't work. So I went to my work (autozone lol) and looked up as many wiring schematics as I could find. According to them, the black/grey wire is the signal wire that goes back to the TCCM to tell it that it has fully engaged, not what tells it to engage/disengage. After playing around with my multimeter on the front actuator, it seems that adding hot to the light blue wire makes it engage and taking it away makes it disengage. But however, when I try to wire 12v hot from the battery to it, it doesn't work. Somebody please help me on this? So as of right now to put it in 4wd, I have to put the tcase in 4x4 then put the fuse back in for the TCCM and it locks the front in. So I need help from someone who has got it to work and took it out and made sure the 4x4 was actually working. And also, does anyone know which wire goes from the TCCM to the ECM that tells the ECM when the tcase has failed and to trip the service 4WD light?
 

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another question... i am doing the same swap in my 01 tahoe. i got a 241 from a 90 3500 dually. i just got it bolted in to my 4l60e. i had the t-case rebuilt to accept the 27 spline output from my trans. but on the 241 there are only 2 plugs, one on the rear of the case, and one other in about the middle. i know to hook up the rear most to what was the rear most plug from my old 246. but i am still a little unclear about what to hook to the other plug on the 241, and how to trick the computer so it wont go into limp mode. i have searched and searched and searched. but i have only found scattered results. some one help!!
 

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btw i have a dana 60 front so no ifs.. should i disconnect the tccm behind the dash and ground that f7 pin? or do i need to do something with the f16 pin as well?
 

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The vss is on the rear cone of the tc. It should be a purple and green wire coming from truck. The other plug near the shift linkage is the 4x4 indicator light.
 

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thanks for the reply, so i will splice the same wires that came from the harness to the 246's vss into the ones coming from the rear of the 241. got it! can i use the plug near the linkage on the 241 to send a signal back to the tccm so my trans will shift when in 4wd? or no??
 

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As for the ground, I used a small nail to insert in the plug with a wire soldered to it running to a switch which was grounded. Turn it on when in low, off when in hi. Check out my build too (z71ton) I tried to post as much as I could and the web links that helped me.
 

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btw i have a dana 60 front so no ifs.. should i disconnect the tccm behind the dash and ground that f7 pin? or do i need to do something with the f16 pin as well?
http://i380.photobucket.com/albums/oo241/myspacejoe_photos/OBSTCCMautotracoutput_zps3564f261.jpg
unplug the tccm and it will get rid of the "service 4wd" message.

then put F7 to ground, on a switch. when you shift into 4lo then flip the switch. this will allow it to shift in 4lo.

dont worry about f16. you don't need to tell the computer when its in 4hi, nothing is different then.


edit: for the VSS......you hook the rearmost plug on the 241 to the green/purple wires on the trucks harness. On my '01 silvy the trucks VSS wires were not in the main tcase harness, but bundled with one of the o2 sensor wire looms. Took me forever to find them damn things.
 

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thank you guys very much for the help!! BrianZ71, are you telling me that the wires that were attached to the 246's vss might not be the purple and green ones i need to splice into the pigtail i have on my 241?
 

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thank you guys very much for the help!! BrianZ71, are you telling me that the wires that were attached to the 246's vss might not be the purple and green ones i need to splice into the pigtail i have on my 241?
Np246 to Np241 Swap *Writeup* - Page 3

Should answer your questions..... did the swap in the same year hoe. It funtions like factory.... no switches on dash for diff or 4lo tables, all controled by shifter..... even kept the nice center counsel w/o hacking it up.

*edit* After reviewing that link i want to shed some light on the 'service 4wd' message. I found that if the tccm & 246's actuator are disconnected, then a ecm reset (dead battery for a week), the message disappeared and hasn't come back since.
 

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thank you guys very much for the help!! BrianZ71, are you telling me that the wires that were attached to the 246's vss might not be the purple and green ones i need to splice into the pigtail i have on my 241?
The vss wires on the truck are purple and green. You splice these onto your pigtail.

What I was trying to say is that you won't find the correct purple/green wires in the big loom that had most of the t case plugs on it. It's bundled up with one of your o2 sensors.

Edit: heres a pic I took while trying to figure it out. This was the main harness that had most ofthe plugs going to the 246 I removed. It was NEITHER set of purple/green wires you see in this picture. The correct wires to tie into were bundled up with one of the 02 sensors for some stupid reason.

 
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