2004 chevy 2500 transfer case problem

[Auto-76]

I have a 04 chevy 2500 & my 4wd don't work. Here's what I did if I raised all four tires up & put the truck in drive all four wheels turn but if you lower the front tires to the ground they stop & the back tires keep turning. I know the problem is in my transfer case but not sure where. The transfer case doesn't make any noise. I've owed this truck for three years & last year put new chain & gears in the transfer case. It drives fine in 2wd . Yes front end actuator is working

[8.1HD/ALLISON]

Is the front axle actuator working?

[Auto-76]

Yes actuator is working. If u have tires off the ground they will turn when you drive the truck. When you lower the truck to the ground the front tires don't pull & the front driveshaft don't turn.

[Auto-76]

Today I pulled the transfer case & took it apart. I found that the pick up tube for the pump in the transfer case came apart. This is a np 246 transfer case it has auto 4wd. Since the pump was not working it burned the clutches up. I got all the parts ordered when I get put back togeather I'll let you know if it works.

[8.1HD/ALLISON]

Sounds good. Any idea how or why the pickup tube came apart?