My transfer case will only pull vacuum to the hubs when floor shifter is in between 4 low and 4 high. as soon as the dash light comes on for low or high it looses vacuum. Is there a switch that tells it to pull vacuum? Does anyone out there have a good breakdown of the transfer case?

 

I don't think I understand what you are saying....When you put your truck in 4 wheel drive the hubs should loose vacuum to allow the hubs to lock into place. When you put it back in 2 wheel drive the hubs should have vacuum to pull the hubs back and disangauge the hubs. In 2 wheel drive your hubs will always have vacuum.

 

My understanding is that vacuum engages the hubs. I could be wroong, hopefully someone out there has gone through this before.

 

Barry

The vacuum keeps your hubs disengaged until you put the truck in 4 wheeldrive then the vacuum releases the hubs and allows them to engage.

 

So in theory with the engine off and vacuum depleated if I jack the front tires off the ground the huds sould be locked in?

 

That would mean in a pinch I could pull the vacuum lines off the hubs and I would have 4 wheel drive?

 

Short answer= yes.

Here's the best trouble shooting info for the 4x4 vacuum system;

https://www.ford-trucks.com/forums/8...then-some.html