1983 jeep wagoneer 4 wheel drive won't engage

I have a 1983 jeep wagoneer limited and it has the vacuum operated 4 wheel drive. When I try to engage the 4 wheel drive it doesn't do anything. I can hear what sounds like vacuum comin to the switch inside, but the 4 wheel drive never engages. I found a spot above the axle where it looks like someone tried to repair the vacuum lines with silicone or something, and I was thinking this would be a good place to start looking for leaks. My question is would it be a good idea to modify this vacuum system to actuate the 4 wheel drive manually with a cable or something? Also wondering if I could modify the transfer case to engage manually in stead of the vacuum operating all of it? I just don't have alot of faith in the vaccum operated 4x4 wondering if anyone has tried this or something similar?

I got under the jeep a little while ago and had my son move the 4wd switch back and forth and I saw the vacuum diaphragm thing on the transfer case was trying to shift the tcase but just barely . And I couldn't make it move even prying with a screw driver? Any ideas...

Ok I think I have narrowed it down to the axle... when I put the 4wd selector on 4 wheel drive and put the transmission in Rev or forward gears the front drive shaft will spin, but it spins when the vehicle not moving also, I don't know if this is normal...any input here would be appreciated...

carnuck wrote: Permanently engage the front axle. Then change the vacuum line to the tcase shift motor so there is only 2. Furthest from the linkage is disengage. Middle one is engage. Plug the third one. That way you can never accidentally shift to 4x4 and destroy the vi$cou$ coupler in the NP229 tcase because the (insert naughty word) front axle didn't engage! More on that on ifsja.org and fsjnetwork.com

Thank you carnuck for your input here I was actually working on the wagoneer today and I got the defrost fixed :) I'm trying to follow you but I can't quite understand what exactly to do I have a few questions..first you said permently engage the front axle. How do I do that? Second I know where the transfer case shift motor is, I understand changing it to two, but when you say furthest from the linkage, do you mean furthest from the front of the vehicle? Just trying to be sure here..third and last question is about the accidently shifting into 4 wheel drive with the front axle failing to engage. How exactly could this happen? Do you mean it could happen right now if I was driving down the road and accidentally shifted into 4 wheel drive? And what do you mean by the vi$cou$ coupler ? Thanks again