[browningbuck225]

My dad has a 2003.5 6.0 with on-the-fly 4x4 engage. He told me today that the 4x4 will not engage. Also his a/c only blows on defrost until he starts moving, that's what I think he said. I told him it may have something to do with the vacuum pump. Because I know that those hubs are engaged by vacuum. If y'all could help me out that would be great!

 

[RT]

Easy enough to hear if its running. More likely a vacuum leak - check the hoses going to the front axle. If its not that, you might need to do this:

Welcome to guzzle's 4x4 Needle Bearing Maintenance Web Page

 

[browningbuck225]

Ok. I'm not familiar with the on the fly shift because mine is manual. What do these lines look like?