Explain the IFS 4x4 system...are front axle shafts always engaged to hubs?

[Big6ft6]

I feel like I should know this, but can anyone explain how the IFS 4x4 system works? I have 1991 k2500 7200gvw. Are the front axle shafts always turning anytime my truck is in motion even in 2wd?

This is what I understand.
1) when I shift the floor lever into 4wd, the transfer case engages the front drive shaft
2) After a pause of varying length the thermal actuator pushes a plunger on the front differential (which does something) and now I have 4wd.

What actually happens when the thermal actuator plunges into the front diff? Does anything happen at the hub or is the hub always locked to the front axle shafts?

 

[dhcomp]

You are in the wrong form, but i'm sure a mod can move the post.

Yes, the CV shafts always spin with the hubs.

The thermal actuator connects the shafts in the front diff to engage the front end.

Tip: The thermal actuators sucks. Upgrade to a 96-99 electric style, or get one of these:
http://www.4x4posi-lok.com/

The thermal ones fail, and take forever when cold. With the posi-lok, you know when its locked.

 

[Big6ft6]

Thanks dhcomp! So when you say "connects the shafts in the front end" does this mean until the thermal actuator plunges in the CV shafts are actually not connected to the carrier?

Sorry about the wrong forum, I saw "75-91 trucks" and figured I was safe but I suppose trucks refers to the HD trucks that still has the solid axle fronts, now I see IFS has its own section...woops Most of my posts have historically been for my 89 burb so I'm not up to speed on the other areas on the forum I'll straighten myself out yet...or get an older truck again

 

[onetonbb74]

only one side is not connected to the carrier, and with an open diff, you have no power until that one side is connected via actuator.

 

[Big6ft6]

Ahhhhh...thanks oneton! That makes more sense..I was trying to think how they would disconnect both cv acles from the carrier via a single plunger on one side of the diff case...

Ok..I'm done taking up space on the wrong forum! Thanks guys!