I just started using my 4wd due to snow, ive used it before to screw off but never for extended periods of time. After having some wicked vibration problems driving home from work, i discovered that my vehicle will be stuck in 4hi when selecting 2hi, unless i reverse a few feet. This bumps it back into 2wd and everything is fine.

So my question is: is this working as intended, or is there an underlying problem? I thought perhaps there was a vacuum line that disengaged 4wd on the vacuum actuator, but it seems to be spring assisted. Could the srping be tired?

 

It doesn't sound like it is working as it should. I would take a look at the front axle engagement cable to see if it is froze up. If it is froze up, then the spring inside the front axle may not be enough to disengage the front axle until you switch directions taking the load off of the engagement collar.