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Discussion Starter · #1 · (Edited)
So I've recently replaced my front diff and I'm not getting any drive from my front wheels while in 4wd. Everything seems to shift into place when I try to shift into 4HI or 4LO, but only the rear wheels spin like it's still in 2wd. If I put the transfer case in 4wd and shift the transmission to neutral and roll the truck, the front drive shaft turns which makes me think that the front diff is in gear, but my front wheels won't spin so I'm not getting any power to the front drive shaft. I've replaced the transfer case motor and the push button switch in the dash and still having the same problems. I know my front diff actuator is good because I had a spare that I tried replacing with no luck. I don't really know what else to do than take out the transfer case and try to rebuild/replace it, but I wanted some other opinions before I do that. Please let me know if there's anything else I could try before I tear into the transfer case.
(Note: The "Service 4wd" light doesn't come on so I'm not sure if it would throw a code)

Truck Details:
2000 Silverado 2500, 4wd, Automatic Transmission, Push button 4wd, 6.0L V8, Regular Cab
 

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So I've recently replaced my front diff and I'm not getting any drive from my front wheels while in 4wd. Everything seems to shift into place when I try to shift into 4HI or 4LO, but only the rear wheels spin like it's still in 2wd. If I put the transfer case in 4wd and shift the transmission to neutral and roll the truck, the front drive shaft turns which makes me think that the front diff is in gear, but my front wheels won't spin so I'm not getting any power to the front drive shaft. I've replaced the transfer case motor and the push button switch in the dash and still having the same problems. I know my front diff actuator is good because I had a spare that I tried replacing with no luck. I don't really know what else to do than take out the transfer case and try to rebuild/replace it, but I wanted some other opinions before I do that. Please let me know if there's anything else I could try before I tear into the transfer case.

Truck Details:
2000 Silverado 2500, 4wd, Automatic Transmission, Push button 4wd, 6.0L V8, Regular Cab
I think you need a Tech2, or find someone with one, to properly diagnose this. Typically I’d expect the actuator motor to be the culprit in this type of situation, but if you have a known good one, sounds like that’s been eliminated as a cause. Also, with the front diff just being replaced, seems likely that has something to do with it.
 

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Discussion Starter · #3 ·
I think you need a Tech2, or find someone with one, to properly diagnose this. Typically I’d expect the actuator motor to be the culprit in this type of situation, but if you have a known good one, sounds like that’s been eliminated as a cause. Also, with the front diff just being replaced, seems likely that has something to do with it.
The reason I replaced the front diff is that the front pinion bearing was locked up, so when I shifted into 4wd my front wheels would lock up and the truck wouldn't go anywhere. Now when I shift into 4wd the truck will move, I just don't have any drive from the front wheels. I'm 99% sure that there's nothing wrong with the front diff or actuator now, and I'm really not sure what else I may have affected by changing out the front diff.
 

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FYI, the front driveshaft will turn whether you are in 2wd or 4wd. It isn’t engaged until you are in 4wd. It free spins in 2wd.


Also, did you replace the tcase motor and rebuild the front diff yourself or get a shop to do it? If a shop did it, I’d take it back to them and get them to see if they could fix the issue you’re having.

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Discussion Starter · #5 ·
FYI, the front driveshaft will turn whether you are in 2wd or 4wd. It isn’t engaged until you are in 4wd. It free spins in 2wd.


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Right, but when I put it in 4wd it no longer free spins, it will turn the front wheels. I jacked the truck up and turned the front shaft with a prybar through the yoke and it does drive the front wheels when I turn it manually
 

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Discussion Starter · #6 ·
FYI, the front driveshaft will turn whether you are in 2wd or 4wd. It isn’t engaged until you are in 4wd. It free spins in 2wd.


Also, did you replace the tcase motor and rebuild the front diff yourself or get a shop to do it? If a shop did it, I’d take it back to them and get them to see if they could fix the issue you’re having.

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Just saw the second part of your post. I got a working front diff from a junkyard so it's used but not rebuilt. And I replaced the tcase motor myself, but I had the same results before and after changing it so I doubt that it's part of my problem
 

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Put it in park, engage 4WD, jack up the front of the truck, and try to turn the front driveshaft. If the tcase is bad, the front driveshaft will spin. If it doesn't, that means the tcase is good because the front driveshaft is locked to the trans and the rear wheels like it should be.
 

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Put it in park, engage 4WD, jack up the front of the truck, and try to turn the front driveshaft. If the tcase is bad, the front driveshaft will spin. If it doesn't, that means the tcase is good because the front driveshaft is locked to the trans and the rear wheels like it should be.
^^^^^This

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Just saw the second part of your post. I got a working front diff from a junkyard so it's used but not rebuilt. And I replaced the tcase motor myself, but I had the same results before and after changing it so I doubt that it's part of my problem
Was the diff you installed from a different year truck? Some differential's were set to have a thermal engage shifter. When fitted with a motor drive servo shifter a small spacer button is needed. This spacer, about the size of a nickel and maybe 3 times as thick is not held in place by anything. Could it be missing? The motor drive servo shifter may need the spacer.
 

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Discussion Starter · #10 ·
Was the diff you installed from a different year truck? Some differential's were set to have a thermal engage shifter. When fitted with a motor drive servo shifter a small spacer button is needed. This spacer, about the size of a nickel and maybe 3 times as thick is not held in place by anything. Could it be missing? The motor drive servo shifter may need the spacer.
I believe it was from the same year, but i'm not 100% sure. Would there be a nameplate on the diff where I could check that? I did a little more testing with the truck on jacks and if I manually turn the front drive shaft, it will turn the front wheels when in 4wd which makes me think the diff is okay. Same thing when I have the rear shaft out with the truck in 4wd, it will lurch forward when I put it in gear (as if the tcase is also in gear) but if I apply any throttle at all, I get no power. Is there some kind of clutch in the tcase that could be slipping when I try to rev it up? Really stumped on this
 

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Discussion Starter · #11 ·
Put it in park, engage 4WD, jack up the front of the truck, and try to turn the front driveshaft. If the tcase is bad, the front driveshaft will spin. If it doesn't, that means the tcase is good because the front driveshaft is locked to the trans and the rear wheels like it should be.
The shaft would not spin when in park and the truck is jacked up, so the tcase should be in gear. And if I manually turn the front shaft while the truck is in neutral, the front tires turn as fast as I can turn the shaft, so it seems the front diff is engaged as well. However, if I have it in gear with the rear shaft out and rev the engine, I get nothing. Correct me if I'm wrong but I think there's some sort of clutch in the transfer case that could be slipping when I try to apply the throttle?
 

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Yeah sounds like the same problem my truck had when I bought it. These trucks with the np246 transfer case use a clutch pack to drive the front wheels. The shift servo compresses the clutches. Most likey worn out clutches. I rebuilt my transfer case and solved the problem

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