I have a '97 Blazer with the 3 button dash mounted buttons. Buttons light up when I switch from 2 HI to 4 HI, no four wheel drive though. Thought it might be the actuator, so I replaced that. Pulled vaccum line off at actuator and I could feel vaccum when in 4WD. Still not working though. I checked under vehicle and it looks like the 3 vaccum lines are hooked up at the transfer case. I got under vehicle and had a buddy switch from 2HI to 4HI. It looks like the front driveshaft is spinning when in 4HI, then when switched to 2HI it's not. Front wheels aren't spinning though. Any ideas on what to try next? Thanks.

 

If the drive shaft is spinning, but the front wheel(s) aren't, sounds like the problem is in your front differential. Drain it and refill it. Check the fluid you drained for a burned smell, silver-metallic shimmer, and or metal shavings. If any metal like substance is found, shimmer or shavings, you are gonna have to replace some or all of the gears in the differential.

~Good Luck~

 

check for cracked vac lines if you have a bad one you could have vacuum at the actuator but not enough to pull the cable far enough to engage the front axle, or save some time and pull the cable by hand and clamp some vice grips on it to test if that engages the front axle or not. Happened to mine last winter, could watch the cable pull when the wife hit 4hi and 4lo buttons but still no engage up front I did the vice grip trick and the axle engaged, put new silicone vac lines on and its been flawless ever since.