Howdy folks! I've finally gotten my 99' blazer back from my mechanic with a (not orginal) rebuilt tranny and used NP236 transfercase (40k km) installed. Took it down the highway, everything feels great- but once I got home and tried to cycle the 4x4, no luck 🙄...

let me start off by saying that Prior to the replacement the 4x4 system was working fully.
Old t-case died cause of the oil-pan-pump-death issue, knocked a hole in the case lost fluid yedeyada-

and prior to this replacement I have already replaced and confirmed the function of everything in the 4x4 system (outside the most important part...the vac lines ) - from the vac switch, to the actuator, 4-button controller and encoder motor.

the one lingering issue from previous work,
Is the excessive wear of the retaining-spring clip for the actuator cable on the differential end. While servicing the leaky axel tube seal I had it off.. and well it just doesn't clip in all that tight... I've also had it off between the old unit dying and the new unit coming in- so it's my prime suspect and I'll be taking the cable off and yanking the pin myself to confirm function of the Tcase later this afternoon.

I've had the battery off 30min and checked all fuses. Crawled around under it and everything is plugged in, same under the hood.

Working under the assumption that it is not the cable or any other hardware related issue... (its like 90% the cable) let's say it's a potential electrical issue- so I go bust out my multimeter and dig out the all the relevant pin-outs, where am I probing 1st?

what exactly is the order of operations for the 4x4 switching process? TCCM checks with the NSS, then the front diff sensor, then it tells the vacuum switch to switch, diff sensor again and then fire the encoder motor?

What would be your next steps?

 

Maybe this will help:

https://blazerforum.com/forum/2nd-ge...-blazer-89044/

 

Thanks! I was looking for this!

Finally got a new actuator cable in, went and hooked everything up- and it seems like its just not pulling the new cable far enough? Or the new cable is slightly too long? (I put them side by side and they seemed pretty dang close if not bang on) the actuator is definitely getting vacuum and squeezing...
-If I pull the cable myself by unscrewing the cable retainer on the end with the sensor housing- I can get the 4hi light to turn solid.

The actuator is new too- and everything was working previously; honestly it's not adding up and hate this vacuum cable nonsense and it's bull**** little clips. I'm going to swap the old cable and actuator back in and try it all again- the whole reason I went down this road was because I ****ed up one of the clips last time I had the cable off, but I've got new clips and I'm well versed in their removal now :/ .....

Im guessing now i have to go buy a vac gauge and start hunting for a line leak?

Does anyone know if there is a 3rd party spring-lever lock thing I could buy and install to bypass this entire system? I don't care about 4hi auto operation, and I don't mind having to crawl under the truck and lock a lever every time I wana use 4hi/4low. I'm going to give the fix one more swing- but if there's not a kit I might just find a machine shop willing to do an odd job...

I JUST WANT THE GEAR OIL TO FINALLY BE ABLE TO STAY IN THE DIFF 😭!

 

When you say you checked the vacuum lines, how did you do that? A visual check is not necessarily enough. They can crack along their length or become loose at the connectors.

As for the cable, have you compared the new one to the old to confirm they are the same length? Have you checked that the amount of travel on the vacuum actuator for the front axle is the same or greater than the distance the engagement gear selector must travel?

I once saw on the forum someone who added a manual actuator for the front axle. It consisted of a long actuator cable that was routed from the axle directly to under the instrument panel. It substituted the action of the axle engagement vacuum actuator. With such a manual version, I don't see why you couldn't still use the Auto 4Hi function.

Check out these links:
https://4x4posi-lok.com/product/chevy-gmc-s-series/
https://blazerforum.com/forum/steeri...-system-96029/

 

AH! Just what I need! 175$+tax and ship, never have to worry about this nonsense ever again? I'm sold!

And I haven't checked all the vac lines, they are probably pooched 🙄, I had the opportunity to replace them when I had the whole front end open and was doing the mainfolds+plugs- and once all that stuff was back in and I realized I needed to do the vac lines... well I kinda just said F* it, because up until my T-case up and died, the 4x4 was working just fine.

Definitely gonna double check the length of the cable when I pull it all back off.

 

Gentlemen. My shame.

I forgot I left this T wide open after taking the intake manifold off. Sealed it up with electrical tape and its working just fine now! Ofcourse since I removed the cable unnecessarily, I have to jack up the front diff, unbolt the tube, unbolt the cable mounting plate, drain the diff, clean the **** out of it, finger-f*k some gasket maker in there for the 3rd dam time....

As always, thank y'all for the information,
ill undoubtedly have to reference this again at some point.

Now let me just go find the nearest wall....

 

Whoops!

I'm always torn between a challenging problem having an easy, but embarrassing solution, vs. the problem being so hard that it was actually deserving of all my effort. LOL

If you need to replace your vacuum hoses, check the link for a thread I've maintained for awhile on doing that. (Someday I'll submit it to be a sticky thread.)

For securing the vacuum hoses, I've used small zip-ties as one-use hose-clamps for them.

 

Okay, I don't know where I went wrong now.

It was working, I went to re-seal everything, it stopped working, Verified the sensor was working, verified the cable was attached, verified the actuator was pulling it, but while in the past I could manually pull the cable myself to turn the light solid, now when I pull the cable, I find I can't pull it any further than the actuator is already pulling it- and the light still isn't turning solid, which means the shaft isn't being pulled far enough to depress that stupid spring ball sensor.

So here's a question- there's a washer and the clutch gear that slide in and out along with the axel tube when you pull it out; I made sure the washer was on - does it matter if the clutch gear was on the tube side or the diff side when reassembling it? I had a jack under the diff and I swear I got everything lined up right.... how far was that shaft supposed to be able come out? I only got it traveling about 1/4"

 

Methinks I got the tube on wrong.

Can I just support the diff with a jack, undue the two big bolts that retain the axle tube and just shift **** around until i can pull the engagement shaft all the way out? Or am I looking at doing the full course again?


EDIT: next day, did infact put tube on wrong. Took it all off, shift fork moves full 3/4 again. Everything works again, just gotta wait for the gasket maker to cure... again..