NP8 transfer case issues

[Bowtied72]

Let me start by saying,  this has been a long and frustrating process. I have read through many threads, in several different forums. I’ve learned quite a bit of useful information, however, none of that has solved my issue. I am working on a 2000 blazer with auto 4wd (NP8 transfer-case)  which is stuck in 4wd. The tccm and encoder motor on t-case seem to be working correctly. I have removed the encoder motor and shifted t-case into 2wd manually but the front driveshaft remains engaged.

Has anyone here encountered and hopefully solved this issue?  
Could it be the clutch plate, or some other internal part in the t-case? OR do I have to replace entire t-case?  

[Bowtied72]

One more detail is I did not drive the vehicle at all after manually shifting to 2wd.  I know on some older models sometimes it helps to back up or at least roll some to disengage, but I thought that was more for the differential than the t-case. 

[davester]

Does the transfer case actually shift into 2wd with the encoder and it's just the front actuator that remains engaged?  As in, you can lift up one of the front wheels, and it will spin, but it takes some effort as the front driveshaft also spins?

[Bowtied72]

Hey, thanks for responding davester. No that’s not the case here unfortunately. Honestly, that’s where I started this journey. My son bought this blazer a few months ago. Runs good but had the typical occasional 4wd issues this setup is prone to. Being stubborn switching in or out of 4lo, but would do so with a couple attempts. Only tried cycling a few times testing it out. My son drove it for a couple weeks. While driving one day the rear diff pinion nut came loose as well as the pinion flange. Which destroyed the diff gears. I installed a used read end and when I took it for a test drive I could hear a humming sound once it got to about 30mph. I thought it was the front diff so I started researching and troubleshooting. Vacuum lines to solenoid and actuator looked dry rotted so I replaced those and tested actuator and diff worked fine. Still had the hum. When the t-case switch was activated I could hear the tccm and encoder motor doing their thing and the lights would on the buttons would blink and then stay solid indicating it had successfully shifted, however even when in 2wd and with trans in neutral I could not turn the front driveshaft. So back tip troubleshooting... I removed the encoder motor,  plugged the 2 connectors back in and cycled through 4wd modes motor appeared to be shifting as it should stopping in 3 different positions depending on which mode was selected. Then I used a crescent wrench to manually shift the transfer case to the 2wd position according to the encoders position front shaft still wouldn’t turn. I tried the other positions just to be thorough and in case the tccm or encoder was going to the wrong position somehow. But same thing the front shaft stayed engaged...I am trying avoid replacing or rebuilding entire t-case unless that’s absolutely the only option. 
 

sorry this is so long winded, just figured I’d map out my journey in case I overlooked something. 
 

[davester]

first, paragraphs are your friend.  it's hard to read a huge block of text like what you wrote.

 

So, when you use the wrench to switch between different modes on the TC, with one of the front wheels off the ground, none of the modes let you spin the front driveshaft?    If this is the case, then somethings busted in the transfer case, probably the mode fork.

[Bowtied72]

lol sorry about the poor format.

 Thanks again for your timely response. 

i was looking at another thread earlier and found a pretty thorough step by step procedural for the rebuild of this model t-case. I plan to read through it tomorrow to get a better understanding of its internal parts and operation. i have never torn a t-case apart and have a basic understanding, at best,  of how they work. 

 

if you are correct about the mode fork being stuck or broken, Am I correct to assume there is likely to be further damage internally?