I have a 77 k5 Blazer w/ a np205 transfer case. Everytime I put it in 4 wheel drive while its in neutral, once I put it in gear it throws it out of 4 wheel drive, If I am able to get it to stay in once I give it a little throttle there is a loud thumping noise coming directly from the transfer case almost like it is slipping in and out of gear...I have had several people tell me different things, anywhere from a snap ring came loose to the gears being bad or also the output shaft needs replaced, anyone have any suggestions or possibly have ran into the same problem? Your help is greatly appreciated....THANKS

 

i wont be much of a help but same thing happened to me on a np203. had to have a friend of mine stand on the lever basically while i was offroading going up and down hills so i didnt wreck. try 4hi or 4low. maybe one of them will work

 

Will it hold in 4LO? If so, your linkage could just be out of adjustment.

 

I can get it to go in 4 low and 4 hi but it does the same thing in both I get a loud thumpng noise like it is slipping in and out of gear...Originally I found that the double cardon was bad and I took the front shaft and had all the u joints and the double cardon replaced but it is still doing it,,,Thanks

 

Your front driveshaft isn't hitting a cross-member is it?

 

Nope, it is free and clear of all cross members...