4x4 not working

Hey yall new on here, the other day I discovered my 4x4 doesn't work on the 99 I just bought, I've narrowed it down to something with the vacuum hoses or the hubs, I'm not entirely sure how to fix this problem and need some help and advice! do you think installing manual hubs would fix it? Thanks yall

 

I spent a few weeks tracking down my problem- solved with help from others here- this was my thread- <A.D.D. help needed>- (Beats me how to link directly). Remove the cover on your transfer case actuator, it's a snug fit, pry it out gently. Clean the contacts, three little copper fingers, and clean the surface they contact, reassemble. In my case it was immediate success. There are photos and step by step posted on the site, I'm not sure exactly where- try "username" for his posts.

 

I went and looked at it! looks good there are loads of information on it but the one problem is I have a manual transfer case....should I still try it?

 

I don't have an ADD setup but I'll take a stab at it.
Try this if you have a manual transfer case
Put the transfer case in 4wd. Lo or Hi, does not matter. Truck not running.
Crawl underneath and see if you can spin the front driveshaft by hand. If it does not turn, the transfer case is working.

By the same token, put the transfer case back in neutral or 2HI and the front driveshaft should spin freely if the front axle disconnect is disconnected.

Most likely it is the ADD system that dp259 mentioned. To be honest, I'm not sure if they are electric or vacuum operated, I see pics of both. This one is vacuum.

 

Be aware that ADD (Automatic Differential Disconnnect) replaces the manual hubs, and is not related to your transfer case.

 

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Okay I did all that and looks like transfer case is working but insane tons of little hose fittings not connected, I'll post pictures tommorrow or tonight depending on when I get the time but I really have no idea if that's what they really are... Thanks guys and please bear with me thought this process I need help lol and it's greatly appreciated