[old_master]

Transfer case operation can get quite technical. I will keep this as easy to understand as possible, so that anyone that reads this, regardless of his or her technical aptitude, can understand it.

The NV233 selectable transfer case has a sprocket on the rear output shaft. The rear drive shaft is connected to that shaft. There is also a sprocket on the front output shaft. The front drive shaft is connected to that shaft. A chain connects the two sprockets so that both drive shafts rotate at the same RPM simultaneously. Any time the vehicle is in motion, both drive shafts, all four axle shafts, and both front and rear differential carriers rotate. The rear axles are both “locked” to the rear differential carrier at all times.

When you change the transfer case "Mode" from 2HI to 4HI, the vacuum actuator, located under the battery, moves a pin that locks the right front axle shaft to the front differential carrier and the front differential now becomes “live”, just like the rear differential.

When you change the “Range” from 4HI to 4LO the encoder motor, mounted on the transfer case, changes the output shaft gear ratio by changing to a different set of gears in the transfer case.

If the pin that locks the right front axle to the front differential carrier remains engaged after changing the mode to 2HI, (as with an actuator or cable failure) the vehicle will remain in 4HI. If the chain now fails between the two output shafts, the front differential carrier, front axle shafts and front drive shaft will still rotate as a unit. However, the assembly will not be “live”. Only the rear wheels will power the vehicle.