Hi everyone,
Today I replaced upper control arms on my 96' 4X4 LS model. 219,000 miles and still running strong. While I had everything apart, I decided that it would be a good preventative measure to go ahead and replace the CV half shafts. Once I got everything back together though, I heard an aweful banging noise from right side as I tried to back the vehicle out of garage.
After some unkind words and some further inspection, I noticed that the right side Inside axle that goes into the tube had come out approx. 3/4 -1". I was able to take a pry bar and simply tap on the end of the axle where the half shafts mount up and after a few taps, the axle went back in.

Here's the problem though, now my 4X4 is inoperable. It was working the other night as where I live, we just got 12-14 inches of snow. It didn't seem like the 4X4 was working to it's full potential however so I'm concerned.

As far as diagnosis on 4X4 system, all I checked was that the actuator under the battery was working and it appeared that the vacuum was drawing it down nicely. New vacuum lines and vacuum switch were installed within last 30,000 miles or last 2 years so I'm thinking it might be internal? When I went to engage 4X4 this year for 1st time, it engaged and then I heard a bang like it popped out. That's when I investigated actuator etc. but now fear I screwed something up by tapping axle back into tube?

Any input would be nice as I am taking to my friend's shop tomorrow to utilize a lift and diagnose this 4X4 scenario.
I will first see if the front driveshaft turns while truck is in park and 4X4 is engaged. I did read the start hear first section about common 4X4 issues but having already done many of those already within the last 30K miles, I'm leaning towards faulty synchros etc. or #9 and #23 parts of the schematics that Captain Hook and others have posted.

This is the last bit of trouble I expect to have before going over the 300K mark with this truck so any help is greatly appreciated in advance!

Chaplain Randy

 

Well, engagement fork is seized internally as we can't pull stud out to engage axles. Going to get a differential at boneyard for $150 at this point. My day is shot!

 

Look into getting the Bravada shaft and tube and swap them out. Much easier and possibly cheaper than swapping out the front diff.

 

will do. I'll check into it.

 

Well, here's what ended up being the issue. The thrust washer between the two axles (inner and outer) on the psgr. side evidently dropped when the outer axle came out during the cv axle swap. After locating new thrust washers and installing a new synchro ring on the fork - probably not needed but since I had it all apart and had one on hand etc. - The 4X4 was now engaging manually while I pulled on the actuator cable for verification.

For newbies on this thread, you can jack up "your right front tire only" and verify if 4x4 will engage by pulling actuator cable from below the battery tray, which must be removed to gain access and turning front right tire when 4X4 switch is on or by pulling actuator cable. If it turns, then you have deeper issues. If it locks up properly, then 4X4 is working. (13mm deep well works with proper extensions)

Ok, after verifying that it would engage properly at axle, I then went ahead and hooked up the actuator cable, filled with proper fluids 80/90 wt and went to the actuator to see if it was engaging.
Well, it looked like it was working so I put it all back together and to my surprise, 4X4 was still not working. Yea sure, still heard clicking and all the things associated with it but no dry pavement wheel hop when engaged.
Took it back apart and removed 4X4 actuator to test. Here's how you verify the actuator is working properly even if engine vacuum still appears to be sucking it down. Push the diaphragm all the way in , like it is pulling the cable and put your finger over the vacuum port and see if it stays. If it stays, then the actuator is still good and there might be a vacuum leak somewhere else. But, as was my case, the diaphragm wouldn't hold so I had to replace it. Now, after everything has been repaired, my 4X4 works awesome and I'm waiting for the next snow storm to have some fun.
In all seriousness, I have found enough information from other threads on this site and have done the proper diagnosis by following suggestions etc. to fix my own Blazer. Thank you to everyone who has gone through this headache prior to me and posting on the Blazer Forum.
Have a great Christmas and remember the reason for the season!
Rev. Randy

P.S. I have brand new Michelins on the truck so the Bravada axle swap wasn't something I wanted to do at this time because excess wear on tires.