So I dont know anything about where to get a vac diagram but I also have 4x4 98 ranger 4.0 and had very many issues with front hubs and vac system and through my journys I learned alot about the whole system and may be able to assist you. Im no car pro mech here but I can tell you that the vac system on these rangers go from the engine to a vac pressure cannister located under front right passenger wheel well behind the bumper kinda. From that vac silinoid it goes to the hubs. The engine uses the vac to pressure the hubs for like you said 30 to 60 sec then that silinoid/vac cannister cuts the vac off holding the pressure from the cannister to the hubs which keeps the hubs locked in unless you have a leak or disengage the 4x4 when you disengage 4x4 the canister lets the pressure off. The hoses between the canister and the hubs are paired together with a 3 way hose splitter which one hose runs out from the canister into a splitter to 2 hose and one goes to the left and other to right hubs. Reason I mention this is because since the cannister holds the pressure after 60 sec if you have a leak in a hub both hubs will disengage because they are paired together. 2 ways to test system! Under front pessenger wheel you can see hub hoses and trace them back to the splitter and further to the canister. At the splitter unhook the hose coming out of cannister at the splitter so you can test it by engaging the 4x4 best to have someone in the truck to do while your watching the hose, first check to see for vac and then let it freely vac to check if the canister cuts it off should cut it off within 60 sec then have it taken out of 4 wheel and plug the hose with finger or tunge sounds weird to use tongue but it is better to use tongue cause its very sencative and can feel the suction well better than finger once you decide lol plug the hose and engage 4x4 it should pressure up and hold pressure no matter how long you stay their but remember the engine pressures it for 60 or so. So you have to wait prox 2 mins or so to check if its holding the pressure once you let off it should leak off but you then should be able to tell if cannister is good or not. The hubs you can check by disconnecting the main hose coming out of the hub at the splitter then jack up the front tire so you can spin it while testing and easy test is to suck on the hose. If it pressures up and holds spin the tire to unsure tire turns drive line but hold pressure on the hose long enough to make sure their is no leak if it leaks off that is you problem and remember if it leaks both will disengage because the vac hoses are paired together then test other side by doing the same on the driver side, the driver side has a longer vac hose but disconnects by another splitter on the driver side wheel well on the frame. Hopefully this will help you out any questions just ask.
Sunday, January 3rd, 2010 AT 5:49 PM