4WD light on but no 4WD

[HawaiianStylin]

On my 91 4WD I bought a couple of years ago, when I bought it the 4WD didn't work and being a broke college student I didn't have the money to fix it. Now I am looking to fix it, but would like to avoid taking it somewhere and paying big bucks. Here is the problem:

When button is pushed the 4WD light comes on, but does not engage. I can kind of hear a chattering sound like that it half engaged? or is trying to, but it never does.

Any ideas would be a big help.

Thanks

 

[MrShorty]

1st question is: which part of the 4WD drivetrain is not engaging: the transfer case or the hubs? From your description, I would guess that the t-case is engaged, but one or both hubs aren't grabbing (being an open diff, only one hub needs to be bad).

 

[HawaiianStylin]

I am pretty sure it is one of the hubs, but not completely positive.