Someone correct me if I'm wrong here. The CAD only diconnects one axle. The other axle will still turn the ring and pinion, which will turn the driveshaft. The only way I know of to keep this from happening is to install lock out hubs. If the light turns on in 4wd and off in 2wd, the CAD should be working correctly.

 

Yeah, I agree, sorta... but, unless he's got a fulltime system without autolocking or manual locking hubs the shaft oughta be still...
OR,
The passenger side automatic hub is obviously not unlocking if the driveshaft keeps turning even though the CAD is disconnecting.

 

The front driveline can spin in some cases. If there happens to be slightly more drag in the spider gears than in the t-case, it can spin the entire diff (although it may or may not be spinning at full wheel speed).

Read THIS.

Look and that fantastically accurate LEGO model I made in the link posted above. If I push that model (in 2wd), the driveline actuall spins, but, it does this because I have no t-case hooked up to the front driveling to provide any drag. THis could be why yours spins....it's not uncommon.

While pushing this model, if I put just a slight amount of drag on the driveline, it stops spinning and the spiders gears start to spin instead.

I would just crawl under your truck, with the engine idling and in 2wd, and just see if you can turn your drive shaft by hand. If it spins, then your CAD is disengageing like it should. If you can't spin it, then it is locked up and then we can diagnose from there.

Note to Smokey: You should read the link above too......ain't no automatic hubs on a CAD axle!

 

Yeah, I agree, sorta... but, unless he's got a fulltime system without autolocking or manual locking hubs the shaft oughta be still...
OR,
The passenger side automatic hub is obviously not unlocking if the driveshaft keeps turning even though the CAD is disconnecting.

CAD did not use auto hubs on either side, they were just drive flanges. With the vehicle idling and in park in 2wd reach under and try to turn the driveshaft by hand, if it turns the axle is disconnecting and it is just internal friction in the rest of the differential that is causing the driveshaft to turn. Switching to a good quality synthetic gear oil may help matters somewhat. If the driveshaft won't turn, verify that all the vacuum lines are in the correct places and the cad vacuum motor cycles freely.

 

    Awesome -and highly accurate- Lego work there Doooood 

I did not say he had a CAD axle with full time...  I said UNLESS 

Picky beggars !

 

Hey guys.. thanks much for the good info.. and YES.. the lego pictures definitely helped!   
Axle, for some reason, is working fine now..  disconnected like it should.  Still not sure why.  Am going to take your advice and change the oil in the differential with some good synthetic oil, and hopefully that will help things.  Next step is to install some manual hubs.  Am also going to change the ATF in the transfer case at the same time..  Just having purchased the truck, I like to know everything is changed, and in good working order.    Again, many thanks!!!  I'm sure this won't be my last post.     

 

mine sticks in the engaged position sometimes too.  Won't hurt anything really, but it leads to a slight mis-trust of the system.
The old backing up trick usually pops it back out, must be a bit of a bind in it.  Plus, if you run it for a bit on a somewhat regular basis even if not needed (on a loose gravel road or such) that seems to help keep things moving smoother.
Won't hurt anything really, but it leads to a slight mis-trust of the system.

If you didn't read the other FAQ's on the page the above link was on, read them too for a bit more info.  If you add manual hubs to bypass the CAD system you'd want to lock the CAD collar too otherwise the CAD will still be doing what it does now.