I find bits and pieces about this issue, and it seems pretty common, but I can never find a straight solution... This is a 95 4x4 s10 Blazer Auto w/OD and a 4.3l Vortec.

When in 2wd, my drivetrain (Sounds and feel like T case) starts making a grinding/whining/rumbling noise that fades in and out.. It's quieter at highway speeds, and gets louder at lower speeds.. it IMMEDIATELY stops when I put my truck in 4wd.

I've found solutions that made sense, such as replacing the vacuum switch on t case because it's leaking vacuum and partially engaging front axle... I replaced this switch... no change... I disconnected, plugged, and manually made sure the front axle was disengaged... no change.. Changed T case, front diff, rear diff, and trans fluids... no change... Replaced 4x4 switch just in case that could make a difference... nope... All vacuum line check and damaged lines replaced... nada

So as far as I know I'm left with the TCCM and Transfer case encoder motor...

Using my best logic, it seems as though when I put my truck into 2wd, my 4wd stays partially engaged... So I'm guessing the encoder isn't fully shifting my t case into 2 hi... 4 hi works great and is nice and quiet...

BACKGROUND: The truck had this sound when I first bought it... I drove it in 2wd for a month or so and the sound went away for roughly 1 year, both in 2hi and 4hi...

Back in january I got in an accident and basically took a semi into my front passenger side tire, effed up the hub and tie rod and upper control arm... I still haven't repaired these things, but the sound still didn't occur for a couple months after this accident...


PLEASE HELP!!! I've spent countless hours trying to resolve this issue and I know there has to be someone who can help me with this!! Without direction I just gonna start pulling my front drive shaft, front axles, and remove the encoder motor and try to shift it manually with pliers... Those are the only courses of action I can think of.. HELP!!

 

Could very well be your encoder. Although mine didn't act as yours does it would periodically blow the 4X4 fuse gradually getting worse until 4WD was unusable. Got a replacement at the salvage yard for $65 solving the problem.

 

Today I did a bit of a "redneck" diagnostic check. I wrapped a length of tape around my front drive shaft just long enough to where it wouldn't drag on the ground and drove my truck in 2wd to the store up the street. When I checked it it was wrapped around the drive shaft, proving that the front end is still engaging and causing my problem. Since this problem didn't start back up until I got in the accident, I figure I need to replace my front passenger hub assy and control arm etc.. to get it back into shape.. Since these parts need to be replaced anyways I will see if this may be causing my problem.. The Control arm is bent bad enough that I think it may be possible that the axle is jammed in far enough to stay partially engaged, spinning my front end and front drive shaft through the axle.. Since it wont be perfectly synchronized with the rear end output, I'm guessing it's causing the 'rumbling' sound I'm experiencing..

I'm strapped for $ right now, so it'll be a while before I can get the parts I need, but when I do, I'll post my results... I've found a lot of people with this exact same problem and that have done the same repairs as I have so far and no definite resolution was ever given to them... I'm hoping my time and effort will help others solve this issue once and for all!

 

you could also take off the front driveshaft

 

Front Driveshaft removal was going to be my next plan of action