GM-GMC: 91 chevy P/U 4wheel drive, cv joints, manual hubs

Question
Recently my 4wheel drive will not ingage in the front. I do not believe it is transfer case since the truck drives fine in 2 wheel. I know little about 4 wheel drive and was wondering what else might be the problem. It was mentioned to me that the Hubs might be the issue. What am I looking for? I replaced brakes and cv-joints on this truck and have no idea what the hubs are.

Answer
Your Chevy does not have front hubs.  Chevy went to IFS (Independent Front Suspension) in 1988 and changed the way the four wheel drive system engages.  Other manufacturers have done the same, and they use either vacuum, electrical solenoids, and/or cables to engage four wheel drive.

There is a cable that runs down to the front differential on most Chevys.  This part of the system is not working and needs to be checked out.  I am not certain if it is electrically controlled or uses vacuum.  It could be the switch that selects four wheel drive, the actuating device, or some other part of the system.

I apologize for not being able to offer more help.  My GMC is the old style with manual hubs and a selection lever on the floor in the cab.