Mine is 97 blazer lt with 3 button switch. 4 hi and lo light up when pressed but no engagement. The rubber actuator diaphragm pulls cable out far enough and holds vacuum. In 4hi there is nothing. when i push 4lo, I hear and feel like it is engaging but I got stuck in 6 inches of snow today and been fishtailing all over the place. I jacked all wheels off the ground and put truck in 4 wheel but only rear wheel turned. I reached underneath and was able to turn front drive shaft about one eighth of a revolution either way then couldn't turn it. In 2hi, I could turn all the way around just like one of the posts said to do. What is the next logical step in diagnosing this? I really appreciate any assistance. There is a lot of good knowledge out there and I've been studying it, I just need some direction. Thanks again!

 

Raise only the right front wheel off the ground, engine at idle, trans in park, select 4WD HI..... you should not be able to rotate the right front wheel by hand. Post your results.

 

I did what exactly what you said and yes, the wheel spins around with no resistance. What does this mean? Does this test apply when in 4lo? When I put it in 4lo, it feels like it engages and drives like in 4.wd but I still fishtail. Am I expecting too much? My full size dodge ram just plows right thru snow in 4hi but it also weighs over5000 pounds. What next diagnosis do I perform to check the 4hi? Thanks for the guidance?

 

If the wheel spins by hand, with no resistance, it means the axle clutch is not engaging the right inner axle to the differential. Yes, it will fish-tail in 2WD. 4WD, no.

Check this thread, it explains how to diagnose it: https://blazerforum.com/forum/2nd-ge...battery-75715/

Post your results.

 

captain hook, I have been studying a lot of your other posts on this same subject. You are very knowledgable. I am going to try to avoid repeating any questions that have already been asked but does the test you mentioned also work when putting gear into 4lo?

 

Norteno,
During a mode shift from 2HI to 4HI, linkage inside the transfer case moves and it pushes the spring loaded ball in the vacuum switch.



The vacuum switch applies vacuum to the axle actuator




which in turn engages the right inner axle shaft with the diferential. During a range shift, (4HI to 4LO) the vacuum switch is not affected and continues to apply vacuum to the axle actuator. So to answer your question, yes, the same results apply to the axle in 4HI and 4LO.

 

Either the little collar inside the axle tube is stripped/busted or the actuator cable is stretched/snapped.

 

Unplug the vacuum line at the axle actuator under the battery tray, connect a vacuum gauge to the vacuum line. Engine at idle, transmission in park, select 4WD. Vacuum gauge should indicate approximately 16". Select 2WD and vacuum should immediately drop to zero. Post your results.

 

Take a c-clamp or vice grips, manually compress the actuator and try this again:
If the wheel still turns, the the issue is in the cable or in the axle. If the wheel doesn't turn, start checking/replacing your vacuum tubing.

 

I measured 16 inches HG of vacuum from line going into actuator. the actuator/rubber diaphram compresses all the way in and holds while truck is running. I tried to compress it further with a c-clamp and/or vice grips but it just doesn't go in any further. I also tried clamping on to the cable and pulling it out some more but could not. When I shut truck off in 4hi or lo, the vacuum gauge dropped to zero (I saw the rubber diaphram inflate). Is this normal?? I tell ya when i go into 4lo, I feel a slight jerk like something is engaging and it drives/feels like it is in 4lo but no 4WD. I still get stuck and slide around. I also noticed a very small residual amount of fluid in the vacuum hose when I disconnected it from the actuator??? I think I'm getting close and I thanks you all again for the great info. One more symptom, when I press button to go back to 4hi from 4lo, I hear a loud clunk just before light goes back to 4hi and I can then go back and forth from 4hi to 2hi without any noticable sounds or feelings.