This(picture) I belive puts the transfercase in to 4x4 mode, AND lets vaccum to the front dive axle 4x4 accuator to put the font end in to 4x4 mode. I noticed some sort of sensor near the front, close to the battery.
On my push botton 4x4 systemI noticedI can get in to four low, it may say Im in four low, and it may not either wayI can tell.I didnt do a vaccum test to see how many pounds of vaccum there is in four low(atthe front acuator). There is enough to make the acuator acuate. In for high there is verry little to no pounds of vaccum so my question is.
Dose this electric acuator do what i just said it does?
Is there an adjustment for it seeing how it lets plenty of vacum in 4low and none in 4high?
The sensor near the front, close to the battery just tell the computer its in 4x4 or something else?
On the front axle where the cable for the front end there is another plug does it just tell the computer it is in 4x4 or something else?
Thanks for any responses

[IMG]local://upfiles/7456/C2A26109772E44D5A51515A1210F334A.jpg[/IMG]

 

There is a vacuum switch on the top of the T-Case, with three lines running to it. One is vacuum supply, one goes to the actuator for the front axle, and the other is a vent line. The picture is of the electrical actuator that shifts the transfer case. The vacuum switch will be in the same neighborhood, toward the drivers side, right up on top. These have been known to corrode, and not work quite right, but, that was in the early 90's, and GM changed the design, and supposedly solved this issue......

 

does it matter how that vacuum plug on top of the transfercase goes on? i noticed a pin on the t-case and a hole on the plug i imagin the hole and pin go together i replaced all vacuum lines from the back of the intake manifold to the transfer case and back to the front axle, from the intake manifold to the vacuum ball, and from the intake manifold to the cruse control.I vacuum tested the front acuator and its fine.
so acording to "heyYou" the vacuum switch on the t-case is bad correct?
when i replaced thevacuum lines i noticedsome fluidgetting up the the plug is this a sign of a bad vacuum switch?

 

That picture does not show the vacuum switch as it is located on the top of the t-case and that picture is showing the bottom best I can tell.

Does 4hi actually engage in the transfer case?? Way to tell is to put it into 4hi, then turn off the truck. Try to turn the front drive shaft. If it turns, then the transfer case is not engaged. If it doesn't, then you are not. This would be a fault of either the switch in the dash, the TCCM (transfer case control module) or the encoder motor (what is shown in the picture).

If the encoder motor doesn't properly engage 4HI, then the vacuum switch will not supply vacuum to the front axle actuator.

You could try to clean the electrical connections at the switch, TCCM, and the encoder motor to see if that helps. I think the TCCM is located in the same spot in the 1st gens as it is in the 2nd gens, behind the passenger side kick panel.

Hope this helps!