The M818 has a air selected sprag type transfer case. There is no dash switch like on big block 88's M925. Moving forward, the transfer case on the M818 has a forward and reverse selection controlled by an air valve on the transmission. When stopped, you should hear a psst of air when shifting from reverse to neutral or any forward gear. If you're not hearing that, your first step is to build air and shut your truck off. If working properly, you should hear the psst of air along with a clunk sound from your transfer case. If not, your second step is to remove the transmission tunnel sheet metal and ensure you have supplied air leading to the top of the transmission. Start there but if your problems are not resolved, you may need to disassemble and clean the actuator on the front of the transfer case. Start with those and post back your results. I once had a truck that had a bolt installed in place of the breather on the top of the manifold on the transmission that would not power the front axle. It didn't pass the first or second test I outlined and I went overzealous and went to step 3. Still didn't work but once I removed the bolt and installed a breather, back in business. Not sure why that bolt was there in this case as it was never privately owned until I picked it up. It did come from a transportation unit so who knows, maybe they didn't want the front axle to be sent power or maybe they wanted to lock the sprag in neutral? Bad things happen when rolling backwards in neutral or a forward gear and vice versa.
drove this type 5 ton during OIF1 with a 5k jp8 trailer and yes most of our company logged in over 20,000 over the desert ect. miles. cool bragging rights but i was out driving my nice condition M818 today in deep new england snow and my guess only the two rear axles were doing their thing. is there any chance the front axle wasn't engaged? don't know what goes on inside the transfer case. nobody was around to view the front tires so thats why I'm asking. Thanx, 88M/67X
