4 wheel drive not working
 

I am going through a divorce and ended up with the 2000 chevy blazer ls. it had not run in 2 years and after a laundry list of parts and elbow grease she lives again. I still have some small issues to deal with. The major concern right now with the crazy weather is the 4 wheel drive. I have went through this fourm looking for the best overall answer. First off when you pushed the button for 4hi or 4 low or even auto 4 wheel drive it would only sit there and blink. I replaced all the vaccum lines and the T connectors. The cable actuator under the battery tray started working. I then pushed the buttons for 4 wheel hi and you can hear it shift and you can put the thing in 4 low and it shifts into 4 low can even tell it is in low range engine races high and truck pulls slow. so i tested it today in some muddy hill. the front wheels are not pulling. so i went back into test mode. i went to check the actuator to double check it and it was still sucked in like it still had vacuum even after i shifter it to 2wd before parking. my blazer has the actuator on firewall that leads to cable actuator. Which place on fire wall actuator does the cable actuator vaccum hose go to top or bottom? could the axle lock switch cause axles not lock in place or do I have bigger problems?

I believe the hose to the actuator should be connected to the bottom port of the firewall solenoid switch. My 2000 is doing similar thing with the lights just blinking. Checked and found a vacuum hose break around master cylinder area. Replaced and now getting around 20" into switch and same out. Applied vacumm to actuator under battery to make sure it wasn't stuck or hung up and can hear it moving. When sitting in garage, engine off, key on, vacuum reservoir full, pushing dash button causes sound under vehicle like something is engaging and can hear TCCM clicking so it would seem as though 4WD is engaging but it is definitely not. This happened many years ago (lights just blinking) and replaced the firewall switch and it was fixed. This time that isn't the solution.

replace the firewall switch

Perhaps I wasn't clear when I wrote,'This time that isn't the solution'. That means I already have changed the firewall solenoid, yet still no 4WD.

sorry, i wasnt paying attention... that what I get for waking up early and trying to think.

Don't worry, I sometimes do the same thing as I tend to read quicker than my brain can compute what I'm reading. Another question I never thought of earlier, or have noticed addressed here, is the Service 4WD indicator light on dash. Just what is it supposed to indicate? Any other suggestions for either of us?

Hey guy's this should help. Not shure its written with your setup, solenoid on firewall but it should not matter. https://blazerforum.com/forum/tech-a...ill-help-7180/

One thing that does not get addressed too often is the spring clip on the vac actuator becoming undone. Everything looks cool but the cable just slips in the actuator connection.

Also in the diy theres a home-made posi-lock write-up. One thing that worked good for me is moving the actuator to the fan shroud. Gives you good vis on how everything is working without the battery tray removal. Just the placement of the bracket not the entire deal.
https://blazerforum.com/forum/attach...ine=1364752747

i replaced the vacuum actuator, tcase switch and lines. The front wheels will not engage. Driveshaft turns and can hear 4wd engage but still no luck. Any ideas?

Good news. 4WD is working once again. Checked TCCM connections, 4WD and ATC fuses (didn't know what that one was, Automatic Transfer Case), pulled battery and tray to check vacuum actuator, applied vacuum to actuator, confirmed operational, holds a vacuum and pulls cable. Only thing left to do was get under vehicle and check other end of cable where it attaches to differential. Another project for another day. Drove vehicle after all that and still nothing. Kept checking 4WD and after 5 miles or so started working. Figures, now that spring is here.