Hello, I'm having a problem knowing what's working correctly or not on my 4-wheel drive system.
I have a '99 Blazer with a 4l60e automatic and auto 4x4. I found out the system is faulty somewhere but fail to understand where.
First, if I'm in 2wd I should be able to, by hand, rotate the front driveshaft no matter what gear the transmission is in, right? I can't.
Second, if, while the vehicle is suspended on four jack stands, all four wheels are driven then the transfer case and front axle (not just one or the other) is locked into either 4hi or 4lo, correct? The light says 2hi.
Third, I know what the inside of a common, open differential looks like and how it works, but is a front differential totally different? If I rotate one front wheel shouldn't the other one rotate also? Or the front driveshaft, if the other wheel won't turn?
Fourth, the vacuum lines, actuator, and cable have all been looked at and appear to be working fine. The cable is not broken and both ends were definately connected, the diaphram holds vacuum all night and the cable returns as soon as the vacuum is released. I added a quart of gear lube yesterday, so it's full now too.
I just never had totally took a 4x4 system apart so I can't seem to visualize exactly what's going on inside.
I apologize for the length, but trust me, if I didn't feel the need......
Thanks in advance for any help.

 

1. If you have the Auto-4wd option, then no, you should not be able to rotate the front driveshaft in 2wd mode. The clutch inside the transfer case that allows for the auto4wd mode has a preload to it. It has drag at all times even when in 2wd. The front axle still disconnects in the passenger side axle tube to lower the parasitic loss of the system.

2. I do not understand your question... When in 2HI with all 4 wheels off the ground, it would not be unheard of to have the driver side tire spin, but you should be able to stop it. The passenger side tire should not spin as the front axle should be disconnected. In either 4wd mode (4HI or 4LO), the front axle should be engaged and be driven by the transfer case. You should still be able to stop one of the front wheels from rotating which will cause the other front wheel to rotate at twice the previous speed due to the open differential in the axle.

3. Front diff is the same inside as pretty much any other design wise. It is packaged a bit different and then there is the passenger prop shaft disconnect in the passenger side extension tube, but other than that, there is a ring, pinion, carrier, and spider gears.

4. The NV236 transfer case (what you have) uses an electronic vacuum solenoid to engage the front axle. This is how the automatic engagement works. There is a thread around here somewhere that details how the whole thing works for both the NV233 transfer case and the NV236 transfer case.

 

In the last couple of weeks we started getting a "service 4wd" light intermittently, but the basic tests proved everything was functioning. I placed it in a low traction (wheel slip) state , pushed 4Hi and it pulled itself out. Then I pushed 2Hi and it sounded and felt like it disengaged. But, later, when steering, (parking, cornering) it felt as though the engine was laboring. I listened close while at a parking lot and tried turning while I shut the engine off and the vibrations continued, leading me to the drivetrain specifically the front axle and possibly the t-case. This is the reason for the previous post. Sorry I didn't mention all of this but I was trying to shorten it up using the facts I knew. By the way, now it seems the buttons are mostly inoperable. If I spend some time playing with them it might shift to another mode, but it says 2Hi now and I thought I'd leave them alone for now.

Updating the above post----Took it for a ride, say about 60mi and the noise is about gone. I don't know, maybe all this time it was just noisy from being low on lube. However the buttons are still pretty much inoperative and the "service 4wd" light still comes on intermittently. I'll be looking for electrical issues tomorrow.
Thank you swartlkk for the front shaft and diff. information, it cleared things up for me. I'm still looking for the NV233 and NV236 threads. All i've come up with is this one from you mentioning it. I'll keep trying. Thanks again!