4 wheel drive not working

[Jminter6001]

I need some help...(first time poster)...My 4 wheel drive will not engage. It's a 2008 GMC 2500HD 6.6.  I lifted the truck on jack stands and put the truck in 4wd, the front axle spins but the tires will not.  Took it to a shop and they said their computers show everything is communicating just fine. No codes. They said to put a new actuator in. So I did, and the front axle spins but the tires still will not spin.  So my question is, what else could be the problem?  I tried it in high and low and I get the same result.

[casey.mikl]

What axle spins? The drive shaft going into the differential? But neither cv axle is spinning? Sounds like the axle isn’t locking or the ring and pinion is not working correctly.


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[Jminter6001]

The axle for the rear tires is spinning. The front axle from the differential is also spinning.

[casey.mikl]

When you say axle, are you talking about drive shaft? So with 4wd engaged. Both front and rear drive shafts are spinning?


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[Jminter6001]

Yep. That's it

[casey.mikl]

Okay. So front drive shaft is spinning but the tires aren’t spinning. Turn the truck key on but not run. Leave truck in park or put it in neutral and have someone go under the front by the differential. Engage the 4wd and see if they hear a motor actuator type noise at the front differential. When the 4wd is actuated. The transfer case actuated as well as the differential


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[Jminter6001]

Ok. Will do. Thanks!!  I'll let you know what happens.

[Jminter6001]

I didn't hear anything. 

[casey.mikl]

Of not hearing anything, then the actuator on the front differential isn’t working.


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[casey.mikl]

Of not hearing anything, then the actuator on the front differential isn’t working.

Looks to be about a $30 part.

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[Jminter6001]

Hmmm...I just put a new actuator in. That's what the shop told me to do too.

[casey.mikl]

Okay if that’s the case then there’s an issue between the switch and actuator. When you shift the switch to 4wd do the lights change and it says your in 4wd?


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[Jminter6001]

I dont have any indicator lights in this truck. It's just the shifter in the floor board. But the shop hooked up their reader, and it said everything was engaging properly. 

[Jminter6001]

Was thinking it could be the wiring to the actuator. But wouldn't that throw a code?

[casey.mikl]

Okay so you have a manual transfer case? I don’t know how the manual transfer case actuates the front actuator. My truck has an electronic transfer case and select off the dash.


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