I have a 2001 LS 4 dr Blazer with the 4 button system with NP8 transfer case. In 2HI the front drive shaft is turning all the time. It's my understanding that it not supposed to except in Auto 4wd. I have replaced the control module behind the kick panel and the 4 button assembly in the dash. How is that controlled, is it electrical or vacuum controlled. What would cause this? Appreciate any advice.

 

The front driveshaft will always turn in a NP8. There are internal clutches in the transfer case that provide varying amounts of torque on the front driveshaft (even a little in 2 hi). However, in 2 hi the front axle is not engaged. It's normal!

 

Thanks for the reply, a local mechanic told me the front drive shaft should not turn in 2hi, only in 4wd or auto 4wd. I realize the front axle isn't engaged in auto 4wd but I was told that with the front shaft spinning all the time it would reduce gas mileage and cause undue wear to something in the front differential. Thanks for the answer