98 Z71 with 243 everything quit working

[Schurkey]

When my Trailblazer did about the same thing, (No 4Hi, no low range, no lights on the switch, nothing but 2Hi) it was a problem inside the transfer case. Ended up with a "Genuine GM rebuilt" transfer case.

I paid the core charge, kept the original transfer case--but I've never gotten around to opening it up to see what's wrong.

 

[JeremyNH]

I just rebuilt my NP243 last month in prep for swapping a 4L60e to 4L80e (1998 Z71). It was actually in fine condition so mostly did it for education. Anyway, one of the things I learned putting it back together is that the position of the output shaft can prevent the the tcase from going into or out of 4x4. The way it works is that the shift motor moves a toothed barrel to engage or disengage splines on the output shaft via a shift fork on a mounting plate. The range of travel is pretty limited, maybe 1/2" or so. When the barrel is rear most it is 2wd, when forward it is 4wd. Moving one step more forward engages a planetary gear for low range via a toothed collar supported by the range fork. There is a circlip that holds the main output shaft in position locking it about the rear VSS housing bearing. If the circlip is broken or missing the shaft can walk forward into the tcase and 4x4 will not disengage and if it walks out it won't engage and stay in 2wd. The output shaft circlip is a known weak point in the tcase and Sonnax makes a kit to upgrade it (100420-02K). When I rebuilt my tcase the circlip looked to be in good shape on removal (I really didn't look too hard) but when reinstalling I couldn't get it to engage very well. Turned out it was a bit deformed. Maybe overstretched when I removed it or maybe bad to begin with. It's significantly thicker that the other circlips though so less "springy" and, as mentioned, is a known point of failure (you can Goggle it and see). I believe the typical failure mode is that it breaks and the output shaft starts to walk out the rear working the VSS housing bearing out as it does. The circlip in question is physically in the tail shaft housing so there isn't any gears for it to get caught up in so you really won't have any immediate observable if it breaks off. If the bearing pops out of the VSS housing journal end of tcase if you're lucky, end of tcase+more if you're not. If the output shaft is out of position the plate that holds the shift and range forks (which is what the shift motor operates) will bind up so the motor won't be able to turn it. I tried this with a wrench. It turns easily if and only if the output shaft circlip is installed keeping the shaft in the right position. There is a detente switch which reports the position of the shift and range forks back to the dash switch and ecm by counting humps in the fork plate. Not saying that's your problem just pointing out that you could have an issue inside the tcase as others have noted. Unless I knew it to be a problem outside the tcase though I'd be worried given the possible consequences if it's not.

 

[Schurkey]

If the output shaft is out of position the plate that holds the shift and range forks (which is what the shift motor operates) will bind up so the motor won't be able to turn it. I tried this with a wrench. It turns easily if and only if the output shaft circlip is installed keeping the shaft in the right position.

Mine won't turn even with the "encoder motor" removed. I bet that's exactly what happened.

THANK YOU!!!

 

[Supercharged111]

Try popping the 4x4 switch out of the dash bezel, plug it back in, and bend it around to see if the lights come back on. I just did this to my 1500 and bending it around makes the lights go on and off, so I ordered a new switch.

 

[thegawd]

I had to order a new switch after my wife drove the truck, thankfully mostly in a straight line 10 kms or so, in 4 low.

she had no idea because the lights only lit up if you hit them pretty hard. I tried to fix this but I couldnt make it work. the switch worked fine, the lights didnt.

she thought she F'd the truck and came inside pretty upset, thinking I'd be upset as whenever the truck breaks she driving it and I'm no where near it. lol.

anyways she got home and I told her to stop freaking out, if it's the transfercase, I have another one for it. relax.

I couldnt figure out how she put it in 4 low without slightly rolling and in neutral. it turns out if you hit 4 low and then shift the shifter from drive to reverse, when the selector briefly passes neutral, 4 low will absolutely engage and when you give it a little gas to go, it locks it in.

some beach!

anyways I made sure she understood all about 4 low and made sure she knew it was just an accident that really shouldn't have happened and showed her the procedure in the owners manual.

the transfercase turned out to be fine.

 

[Supercharged111]

I had to order a new switch after my wife drove the truck, thankfully mostly in a straight line 10 kms or so, in 3 low. she had no idea because the lights only lit up if you hit them pretty hard. I tried to fix this but I couldnt make it work. thw switch worked fine, the lights didnt.

she thought she F'd the truck and came inside pretty upset, thinking I'd be upset as whenever the truck breaks she driving it and I'm no where near it. lol.

anyways she got home and I told her to stop freaking out, if it's the transfercase, I have another one for it. relax. I couldnt figure out how she put it in 4 low without slightly rolling and in neutral. it turns out if you hit 4 low and then shift the shifter from drive to reverse, whe the selector briefly passes neutral 4 low will absolutely engage and when you give it a little gas to go, it locks it.

some beach.

anyways I made sure she understood all about 4 low and made sure she knew it was just an accident that really shouldn't have happened and showed her the procedure in the owners manual.

the transfercase turned out to be fine.

I pop my dually in and out of 4lo at a standstill in neutral all the time. I get the same/better results than if I were creeping along.

 

[caseyjones_81]

I just rebuilt my NP243 last month in prep for swapping a 4L60e to 4L80e (1998 Z71). It was actually in fine condition so mostly did it for education. Anyway, one of the things I learned putting it back together is that the position of the output shaft can prevent the the tcase from going into or out of 4x4. The way it works is that the shift motor moves a toothed barrel to engage or disengage splines on the output shaft via a shift fork on a mounting plate. The range of travel is pretty limited, maybe 1/2" or so. When the barrel is rear most it is 2wd, when forward it is 4wd. Moving one step more forward engages a planetary gear for low range via a toothed collar supported by the range fork. There is a circlip that holds the main output shaft in position locking it about the rear VSS housing bearing. If the circlip is broken or missing the shaft can walk forward into the tcase and 4x4 will not disengage and if it walks out it won't engage and stay in 2wd. The output shaft circlip is a known weak point in the tcase and Sonnax makes a kit to upgrade it (100420-02K). When I rebuilt my tcase the circlip looked to be in good shape on removal (I really didn't look too hard) but when reinstalling I couldn't get it to engage very well. Turned out it was a bit deformed. Maybe overstretched when I removed it or maybe bad to begin with. It's significantly thicker that the other circlips though so less "springy" and, as mentioned, is a known point of failure (you can Goggle it and see). I believe the typical failure mode is that it breaks and the output shaft starts to walk out the rear working the VSS housing bearing out as it does. The circlip in question is physically in the tail shaft housing so there isn't any gears for it to get caught up in so you really won't have any immediate observable if it breaks off. If the bearing pops out of the VSS housing journal end of tcase if you're lucky, end of tcase+more if you're not. If the output shaft is out of position the plate that holds the shift and range forks (which is what the shift motor operates) will bind up so the motor won't be able to turn it. I tried this with a wrench. It turns easily if and only if the output shaft circlip is installed keeping the shaft in the right position. There is a detente switch which reports the position of the shift and range forks back to the dash switch and ecm by counting humps in the fork plate. Not saying that's your problem just pointing out that you could have an issue inside the tcase as others have noted. Unless I knew it to be a problem outside the tcase though I'd be worried given the possible consequences if it's not.

Ok thanks you, that’s very good info to have. I’m going to pull the T case and trans harness out completely and check it from one end to the other and put new loom on it while it’s out and then I’ll either find the prob or rule out that issue and dig deeper into the t case itself.

 

[Supercharged111]

I just rebuilt my NP243 last month in prep for swapping a 4L60e to 4L80e (1998 Z71). It was actually in fine condition so mostly did it for education. Anyway, one of the things I learned putting it back together is that the position of the output shaft can prevent the the tcase from going into or out of 4x4. The way it works is that the shift motor moves a toothed barrel to engage or disengage splines on the output shaft via a shift fork on a mounting plate. The range of travel is pretty limited, maybe 1/2" or so. When the barrel is rear most it is 2wd, when forward it is 4wd. Moving one step more forward engages a planetary gear for low range via a toothed collar supported by the range fork. There is a circlip that holds the main output shaft in position locking it about the rear VSS housing bearing. If the circlip is broken or missing the shaft can walk forward into the tcase and 4x4 will not disengage and if it walks out it won't engage and stay in 2wd. The output shaft circlip is a known weak point in the tcase and Sonnax makes a kit to upgrade it (100420-02K). When I rebuilt my tcase the circlip looked to be in good shape on removal (I really didn't look too hard) but when reinstalling I couldn't get it to engage very well. Turned out it was a bit deformed. Maybe overstretched when I removed it or maybe bad to begin with. It's significantly thicker that the other circlips though so less "springy" and, as mentioned, is a known point of failure (you can Goggle it and see). I believe the typical failure mode is that it breaks and the output shaft starts to walk out the rear working the VSS housing bearing out as it does. The circlip in question is physically in the tail shaft housing so there isn't any gears for it to get caught up in so you really won't have any immediate observable if it breaks off. If the bearing pops out of the VSS housing journal end of tcase if you're lucky, end of tcase+more if you're not. If the output shaft is out of position the plate that holds the shift and range forks (which is what the shift motor operates) will bind up so the motor won't be able to turn it. I tried this with a wrench. It turns easily if and only if the output shaft circlip is installed keeping the shaft in the right position. There is a detente switch which reports the position of the shift and range forks back to the dash switch and ecm by counting humps in the fork plate. Not saying that's your problem just pointing out that you could have an issue inside the tcase as others have noted. Unless I knew it to be a problem outside the tcase though I'd be worried given the possible consequences if it's not.

Reading this again now got me to thinking, could this be the same circlip I installed an eliminator for in my 243? I cracked mine open when I did the 4L80 swap and I believe that clip went on the output shaft. I have no idea what I used and didn't take pics either. This is the first I'm hearing of the problem it prevents.

 

[JeremyNH]

Reading this again now got me to thinking, could this be the same circlip I installed an eliminator for in my 243? I cracked mine open when I did the 4L80 swap and I believe that clip went on the output shaft. I have no idea what I used and didn't take pics either. This is the first I'm hearing of the problem it prevents.

That's the one. Only one circlip on the output shaft. Sonnax marketed it as a "case saver" but the typical "case saver" is a collar that goes about the oil pump that is N/A to the np243. The Sonnax upgrade is a split collar with a retention ring held in place by a standard circlip. I only found it when I googled for a replacement when I couldn't get mine to seat.

 

[caseyjones_81]

You really just started changing parts, just guessing no diagnostics, no troubleshooting. Do you have the free service manuals available here? You might start there first. It may explain have the condition your experienceing.

I had to order a new switch after my wife drove the truck, thankfully mostly in a straight line 10 kms or so, in 4 low.

she had no idea because the lights only lit up if you hit them pretty hard. I tried to fix this but I couldnt make it work. the switch worked fine, the lights didnt.

she thought she F'd the truck and came inside pretty upset, thinking I'd be upset as whenever the truck breaks she driving it and I'm no where near it. lol.

anyways she got home and I told her to stop freaking out, if it's the transfercase, I have another one for it. relax.

I couldnt figure out how she put it in 4 low without slightly rolling and in neutral. it turns out if you hit 4 low and then shift the shifter from drive to reverse, when the selector briefly passes neutral, 4 low will absolutely engage and when you give it a little gas to go, it locks it in.

some beach!

anyways I made sure she understood all about 4 low and made sure she knew it was just an accident that really shouldn't have happened and showed her the procedure in the owners manual.

the transfercase turned out to be fine.

So I’ve been digging deep into this truck trying to fix it. I pulled the transfer case wire harness out from under the truck to physically check every wire and re loom it since it was all crispy and falling off. Everything was good on the harness. While it was out I did a continuity test on each wire and it’s corresponding plug terminal. I put it back in and started on checking continuity from TCCM to the T case harness plug in by the brake booster, all is good there. Now I’m checking continuity from TCCM to the push button selector switch on the dash and all was good until I get to the ignition fused circuit and the ground circuit. I have continuity from the ignition circuit when touching it to the ground circuit. It even goes off if I touch it to the metal bar under the dash. So now I’m confused, I can see the ground circuit having continuity to the bar cause it’s a ground. But the ignition hot wire shouldn’t have continuity to the bar at all, in my mind that’s a direct short. But wouldn’t that pop a fuse somewhere or melt the wire that’s causing the short? Or am I not thinking right? I checked the voltage and the voltages show that the ground is normal and the ignition hot is normal. Also the park/neutral switch wires have continuity with the ground and ignition wires as well. Does anything stand out to anyone that I’m not thinking with all of this? I think I’m close to figuring it out now I just can’t get pin point what’s the deal. Before each circuit only had continuity to its own ends, but now this 4x4 push button switch and TCCM have 4-6 wires that share continuity together instead of each having it on their own circuit.