check the vacuum to the disconnect motor before replacing it. a vacuum leak will stop it from working. there are 2 lines. with the engine running you will have vacuum on one line in 2 wheel drive, and vacuum on the other line in 4 wheel drive. if you don't, check the vacuum switch on the transfer case. if it is ok, check for engine vacuum at the switch. you can also test the disconnect itself with a vacuum pump. be careful of the 4 7/16 bolts that hold the disconnect to the axle. the bolts are tining and they break very easy.