HELP with Transfer case

I am having a problem with the transfer case on my truck, when i put it into 4-high it engages and drives all 4 wheels. But, after a varying amount of time ( sometimes 2 min, could be 30 min) it slips out of 4x4, and i hear a buzzing noise ( wounds like the gears are not meshing anymore. It hasen't happened yet when i'm in 4-low. Anybody have the same prob? what should i do. I've heard that the t-case is really expense to fix, is this true? I just got the truck a few weeks ago, and this is the only major prob., although i had to have one of the alternators rebuilt.

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I had the exact same problem with my M1009 Blazer. The shift fork selector was worn out. The forks have a small plastic pad on the tips that rides in a groove in the gear cluster. The pads wear out and then the aluminum fork wears out. That allows the case to slip from 4x4 to 4x2. The range fork doesn't get near the wear as the 4x4 fork so it is usually in good shape. Tear your case down, replace the forks, and do the bearings/chain/seals while you are at it. It is an easy garage project with a Haynes manual

[dito] Had the exact same thing happen on my NP208. about $18 for a new one and half a days work to rebuild it myself and she was good as new.

Thanks, once it warms up a little i'll be pulling the t-case and replacing the fork. Do you have a part number for it? my truck has the np208.

My military manual shows it to be 14029107 and stock number 2520-01-164-6228. You may have to call a Chevy house and have them cross-reference the number to get the correct part number if this one doesnt produce any results.