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Got some snow recently so I locked the hubs on my '77 F150 while driving on some snowy roads. With the hubs locked but still in 2WD, I heard a metallic clinking sound coming from the transfer case (NP203) that would increase in rate/intensity as the vehicle’s speed would increase. It went away when I would shift into 4 hi or low, and when I unlocked the hubs. I contacted the previous owner who has been incredibly generous with emails whenever I have questions (I'm a bit of a newbie when it comes to repairs) and his recommendation was to first lube the case and if that doesn't work, remove the front driveshaft, repeat what caused the noise, and see if it's still there. If the noise was gone, then perhaps the issue is a worn driveshaft or u-joints. My neighbor used to be a ford mechanic and thought it wasn't a big deal, that it's just the sound the driveshaft makes when the hubs are locked. I'm sure somebody here has some knowledge about this, and I'd greatly appreciate any helpful advice before I start wrenching. Thanks in advance!
X2 he is correct on his suggestion. It could be chain slap you heard. Since your NP-203 is chain driven not gear to gear like a NP-205. You know you do NOT use 89/90 gear oil in a NP-203 correct? More like 50W non detergent.
You also know that your xfer case is "splash lubed" and you need to run it in 4wd ever so often (on a dirt or gravel road) to get the lube splashed around in there on that drive chain.
