I have a 96 Blazer with the 3 button dash switch. I replaced the actuator, the actuator cable going to the front diff., & the transfer case switch on the transfer case itself. However my 4wd is STILL not working correctly. It only works when I psychically push the actuator in myself with my hand. It doesn't suck itself in when I engage to 4Hi or 4Lo. But the 4wd works when I pull the cable by hand. I understand this is more than likely a vacuum issue. I checked all the lines & they seem to be fine. I made sure all of my connections were right. I just don't know what else I could look into. Would a manual cable that I activate myself in the cab be a good idea?

 

Im sorry for the bad quality picture but i took a picture of my gm service manual

the line for the actuator for your front end comes from the transfer case switch

so you need to check it by following the whole line to the tcase switch . You might have a leak causing no vac to pull the cable

 

Thanks for the help! I will look into that.

Another thing I noticed the other day was when I was using my heat the air was only blowing through the defrost vent by the windshield. Now could this all be related to a vacuum issue?

 

possibly

 

is your transfer case engaging if so you wouldnt be getting vacume to the actuator. there is a bypass to this that is actually much better so you can use 2wd high 2wd low 4wd high and 4wd low.
here is the link to it https://blazerforum.com/forum/tech-a...-system-31138/ . i am actually considering getting rid of my vacume actuator and doing this modification much more reliable, usefull, and kinda adds a cool factor in my opinion.

 

yup he said it engages and when he pulls the cable manually the front wheels lock so its the line from the tcase switch to the actuator.

it is nice to put a manual like you said I was going that path till i found out my cable was seized causing my front axles not to engage

 

I will inspect the lines tomorrow. I've never had a vacuum issue before. So this is all new to me. I might do the manual cable set up to engage it myself without having to reply on a actuator, but then my heat only blowing through the defrost vents would be my other problem from the vacuum issue. So I think my best bet is just to check over the lines. I just wasn't sure if there was anything else that's prone to failure on these trucks that cause these symptoms.

 

its common for these lines to melt on the exhaust system

a small crack in the vac line could cause not enough to pull the cable also

 

the vacumn line is chaffed thru on the top of the right side of the trans,or the line is off of the round canister,or the line is split somewhere.the system works very good if the lines are ok.

 

Well today I actually replaced most of the vacuum lines. Only one of them had burn mark going through. My heat does blow out the vents now, but the 4wd actuator is not engaging when I hit 4Hi. It still only works if I pull on the cable. So I've pretty much decided to just do away with the vacuum issue & go with a homemade posi-lock thing. I hate to give up, but I spent around 6 hours trying to figure out what is going wrong.