lost front wheel drive in 4 wheel drive

Broken axle!!!!!!!! Put the transfer case in neutral and see if you can turn the drive shaft with your hand. If you can, with both hubs locked in, then you have something broken. Alternately you can put the transfer case in gear and jack one wheel just off the ground and see if you can turn the wheel/tire. If you can same answer, broken axle. It could also be a broken gear set but you will usually hear a lot of noise when that happens. The good news is that the axle is easier/cheaper than the gear set.

As mentioned, broken axle is a possibility, could also be a broken hub or inner gear parts. Any one damaged component will allow loss of drive. As the other gentleman mentioned, hubs locked, and both wheels on the ground, you should not be able to turn the driveshaft. If you can, note whether either axle u-joint is turning (indicating a damaged hub) If neither axle is turning that would indicate damaged internal (spider or side) gears. Make sure the problem isnt in your transfer case by unlocking the hubs (or lifting the front end off the ground) at that point you should not be able to turn your driveshaft because the t/case is in 4wd. Hope this is some help

I would suggest the manual locking hubs, leave the t/case in nuetral, lock one hub at a time, try to turn the shaft at the u-joint at the wheel with the hub locked, should not turn (wheel on the ground) if it does turn with the hub locked, either the hub is damaged or you may find a broken stub axle (the short one from the u-joint to the hub) The hubs are designed to be a fuse, easier and cheaper to repair/replace than other components. You will need allan wrench's and snap ring pliers (depending on what make and model of hubs you have.