How's it going I have a 99 two door blazer s10 my 4 hi will not engage but my 4 lo will only when in 4 lo it will just rev way up and won't shift can anybody point my in the right direction of what to check I don't think it could be the vaccum system because the 4 lo will engage so I don't know what else it could be thanks in advance

 

Have you checked to make sure the diff and transfer box are full of oil?

 

Start your search here in the DIY Tech section. There's full diagnostic writeups for tons of common and not so common issues with the Blazers.