I own a 1994 k5 Sport Blazer 5.7l 4wd. I have had the factory actuator upgraded in 2011, but I continue to have constant problems with either the 4wd will not engage, or I am partially engaged in 4wd and cannot get back into 2wd. I replace actuators sometimes more than once per year. I found a problem that was corrected by replacing the switch on top of the differential, as when it got wet, the 4wd would attempt to engage, but not fully. But now I have another failing actuator 6 months later.


So my question is- what could be causing constant 4wd actuators to fail, even with a 2011 upgrade??

 

It is a so-so engagement mechanism even with the worm-gear drive motor that was the upgrade which was a HUGE improvement over the thermo-mechanical engagement device that came from the factory on it. If you continually think that the actuator is going bad, you may want to look into the wiring that was added when the upgrade was installed to ensure that all of the connections are still clean, sealed, and getting good continuity to the circuits they attached to.

If that all checks out, you should then check the shift fork inside the front axle to see if it is unreasonably difficult to push in. It should not be all that hard to engage the shift fork if you have the passenger wheel off the ground and are able to turn it while you press in on the shift fork. If it is difficult to push in and engage, then you might want to drop the passenger side extension housing to take a look at the condition of the slip clutch and mating splined components. Attached is an illustration showing the inner workings of the front axle engagement system in your truck.

Also, with each replacement of the actuator, did you make sure that the spacer that came with the upgrade harness was still in the hole that the actuator threads into? Without the spacer, the actuator cannot push the shift fork far enough to fully engage the slip clutch. What can happen then is that the slip clutch and/or the mating component can strip out.

If you wanted to eliminate the actuator all together, you can go to a posi-lok setup.

Not to push you away from this site, but you might find more reading material through searching on one of the larger truck sites. Your truck really isn't supported here as it isn't a traditional K5. It is more of a shortened Tahoe or a K1500 pickup with a permanent cap in the back and shares nothing but the Blazer name with the 91 and older K5s.

 

my son opened up the area where the wiring harness had wires soldered, and found a poor soldering job by the Dealer, and frayed and loose wire ends- all is cleaned up now, so we will see what happens as time passes now. Thanks for the detailed reply.


and my K5 Blazer is NOT a REAl K5 Blazer?????? Actually a '95 on Tahoe is either a short Suburban, or a 4 door versin of my era truck, not that mine is a short Tahoe........

 

Hopefully the wiring problems were the end of it. If not, I detailed quite a few other things to check.

As far as the K5 thing. K5 stopped being the model designation of the fullsize 2-door SUVs in '87 with the introduction of the round bodies in the trucks, the Blazer & Suburban changed from the previous C/K designation to R/V (2wd/4wd). Also, the 1500 nomenclature started for the 1/2 ton trucks at that time. The K5 Blazer was most known for it's removable top & solid front axle, neither of which are present in the 92+ fullsize Blazer which later was renamed to Tahoe Sport.