my buddy has a 99 grand cherokee, AWD, 4.7 v8, automatic, he was telling me he was driving home in the nasty snow storm we had up here in northeast pa, put it in 4 low and he said at one point he heard a clunking noise, then a grinding, and then his jeep wouldnt go any further,everything is fine in regular AWD, but when he tries to engage 4 low, he just hears a grinding noise, and he cant engage the lever into 4 low completely, i got a feeling he sheared off something in the t-case, but i would rather get your guys input on this, thanks

 

before you get worried check the linkage. sometimes if you do not use 4 low for a while the linkage wont move freely enough to allow it to go into gear. the grinding noise and clunking is what happens when its not fully engaged. have him turn off the engine and try to move it into 4lo while drifting slowly down a hill, like 1/2 mph.