I have some issues with my 4wd system on my 98 LT Blazer (rhd) with the 4 button auto 4wd)

Everything seems to operate fine but it doesn't actually drive the front wheels.

The controls buttons work and I can move in and out of all modes.
The TCCM clicks when doing this
I hear cluncks etc from the transfercase/gearbox when doing this
The Vaccum Actuator works and locks the front axles together in 4wd
The gear ratio changes when in 4wd low

But the front wheels are still not driven???

 

Anyone got any ideas??

 

you can notice a gear ratio change in 4 low but its still not driving the front wheels? sounds odd...I'm sure someone here has a good idea.....

 

Still facing issues with this, and hoping somebody has some ideas,

Heres what I know:

The buttons on the dash work flawlessly, it changes in and out of all modes without a problem
The vacuum to the front actuator is OK - The actuator pulls the cable and holds it (when I remove the vacuum line I get errors on the dash)

When in 4wd and with the front corner jacked up the wheel has resistence but I can turn it with a bit of force.
When in does turn the front drive shaft turns with it (it is slipping in the transfer case)
When whole thing is on jack stands it appears to drive all wheels and seems to not have an issue at all!

Put in on the ground and go and get a bit stuck and it is clear the front wheels are doing absolutely nothing to help the rears???

I would appeciate any help at all on this I'm in New Zealand and there are no dealers close by who would have any clues about this particular truck so would cost me a fortune in troubleshooting and parts if they don't know what they are doing!

 

Sounds like the clutch inside the transfer case is not functioning properly. What do you have for fluid in the transfer case? The NVG-236 2speed automatic transfer case requires GM Autotrak 2 fluid for proper operation of the clutch which will be blue in color.

Diagnosing the transfer case beyond that requires the use of a tech 2 scan tool or equivalent:

No Correction For Slip In AWD Mode


Test Description
The numbers below refer to the step numbers on the diagnostic table.

2. Helps determine whether the front axle switch is functioning properly.
3. Helps determine whether the front axle switch is locking and unlocking.
4. Tests transfer case clutch performance.

Step #4 is the one that I would be interested in. Hopefully it is something simple because if it is the clutch, then your looking at replacing the transfer case.

 

Thanks, Gives me something more to look at,

The diag sheet lists changing from AWD to 4WD? I didn't think AWD would be an option with the 4wd setup it has 2wd 4hi, 4lo, I thought the AWD was only available in some models and was locked in AWD the whole time with a split ratio between the rear and front, or is AWD referring to 2wd?

Not sure on the fluid situation, I will check this out - the vehicle I believe has been like this since I got it but I did not notice until I took it offroad as the system tells me everything is working OK, Hoping its not a replacement transfer case or this baby is down the road!

Whats your thoughts on the transfer encoder motor? I have read a lot of things reating to the encoder not operating properly that will cause similar things but the act that the system tells me it is engaging is different to all the related problems I have read about, for most peopl eit seems the lights will flash when changing modes but it will return to the previous mode when it times out waiting for a response from the transfer case/front axel.

Your hel p is much appreciated!

 

In this case, AWD is the Auto4wd mode. There is a clutch inside the transfer case that can shift power to the front axle when it is needed when in the Auto4wd mode. The TCCM also disconnects the front axle when in Auto4wd mode and the front axle is not requested.

It sounds as though the encoder motor is doing what it is supposed to be doing. Else you would be getting a "service 4WD" light or blinking 4wd switch lights.

 

Sweet - I took the AWD to be All Wheel Drive not Auto 4wd, I had just woken up!

I am replacing the vacuum actuator and cable later today as the cable outer is a bit dodgy, it still seems to be working but will replace it all anyway, then will start looking at the transfer case etc

 

Alrighty, I replaced the vacuum actuator/cable and assembly - Didn't make a difference which I thought would be the case.

I checked the fluid in the transfer case and I wouldn't class it as blue, it is definately black I can't see any shade of blue in it.

Could the wrong fluid alone cause this problem? or would it be more likely the wrong fluid cause damage that resulted in the problem?

- I will try and track down some correct fluid tomorrow and replace it. Will also be trying to soure a scan tool

Now I have wrecked the front bumper down the road trying it out, nosed the front end into a ditch and the bumper got caught and ripped the number plate area right off!!!! What a pain in the A$$

 

If the fluid is black, then something has gone wrong inside the transfer case. You can put new fluid into it (GM Autotrak2 - buy 2 qts, fill until it spills out the fill port) and hope that it fixes the problem, but I suspect that the clutch is gone. The clutch is what is responsible for transferring power to the front axle. If that has fried, your best bet would be to find a used NVG236 transfer case and swap it out.