This new old guy just found this site and I need help!
Well folks here is my story. The truck is a 96 S-10 4.3L 4dr Blazer with 138,000 miles. I left on a 850 mile trip pulling a trailer and at about 300 miles I pulled off the slab for gas and when I slowed down I heard a noise which sounded like I was driving over those "wake up grooves". I got gas and was directed to a repair shop to check it out. It was late in the day but these nice guys in Hartland VT. took a look and the one mechanic said he knew the problem. They stayed late and because the parts weren't available they removed the sliding collar gear in the front differential. He claimed it needed a new set of thrust washers and maybe a gear. Bottom line is no more noise and no 4wd. But it's June and I won't need it till Nov. where I am. The rest of the trip went fine and when I got back I read here and checked my Haynes, the Haynes is use less IMO. So what do I order ? And does this sound like that was the problem or is something else a miss? My truck is a three button and I guess has a 233 transfer case. Any help would really be appreciated as all I know about 4wd is the workings of my 67 Dodge M37 which is all mechanical with lock out hubs.

 

If the collar does not slide over the teeth on the outer passenger side axle shaft, then it needs to be replaced and you will likely have to de-burr the teeth on the axle shaft.

The actual cause of the problem is likely not in the front axle, but could be a faulty vacuum switch at the transfer case, or a frozen front axle actuator cable.

 

Thanks much, I did spend some time searching old posts here on the subject and have a better idea of how it works. I also looked at the sliding coupling and noticed on one side the face is perfectly flat, yet the other side looks like the teeth have a bevel. If the collar is OK that way then the flat face must go towards the Diff and the bevels help in the right axle engagement? But as I was looking over the mechanics shoulder it looked like both the Diff spud gear and the gear on the right axle also looked beveled. I wish I saw better when they pulled that collar gear to see the orientation.

 

That bevel might be from things slipping too much. You just have to make sure that there is no material pushed over into the grooves between the teeth causing an interference fit or it will never want to go together.

 

Thank you for your input and I do have a further observation. I found the following thread and where Roudy4X4 spent some time describing the operation of the sliding collar. Please read his description and the part numbers he calls out.
https://blazerforum.com/forum/showth...ghlight=collar

If all my reading is correct the #22 sliding collar is held against #23 by the fork under spring pressure. The vacuum pot pulls the fork and the collar slides towards the RS axle onto # 9 the carrier connector and the front axle is engaged. Please understand I'm not trying to nit pick but just trying to understand since I didn't pull the collar out and each side is different on the collar, I do need to know how the slider works.

 

To use the terms from the exploded view referenced...

The sleeve (#22) is not held against anything. It floats on the shift fork (#17). The sleeve is always engaged onto the output shaft (#23) from the differential. The shift fork is held against the carrier case half (#29) by the return spring (#16). When the actuator pulls on the cable, the shift fork moves to the right, engaging the sleeve onto the carrier connector (#9).

The problem you are experiencing is that the sleeve (#22) and the carrier connector (#9) have worn to the point that they will not engage properly. This most often results from a sticking cable or a cracked vacuum line causing the sleeve to only partially engage, allowing it to slip, grind, grab, slip, grind, etc until the "teeth" inside the sleeve and outside the carrier connector are beveled and partially blocking the engagement.

The description given in that post is actually backwards to how it actually works. What I have stated above is correct.

 

Excellent, That is how I read the operation from a mechanical way. Now I know which way the collar gets installed. The vacuum actuator and cable will be checked. The only thing that has me stumped is why did it show up now when I was in 2WD since last march? No matter I'll report back with the results. Thanks again from this combat disabled vet.

 

Hope you don't mind If I chime in? I have a '98 blazer and think the front transfer case is partially engaged when only 2WD is selected.

I found the Vacuum actuator under battery was under full vacuum and the cable at the front transfercase was pulled to the passinger side shaft , and when I pulled the transfer case switch ( the switch with a ball and two electrical pins) I could see the little half moon at the end of the cable that is suppose to signal the ball switch.
Does this confirn that the front wheel drive is engaged?

If I remove the vaccum line and let the cable loose (without vacuum) I should definately be disengaged correct?

When i press either 2WD or 4WD Hi I can here a click at the (motor) at rear transfer case but nor really a motorized action, Could this mean the motor encoder is not working correctly?