vaccum pump
 

I started having problems with my vents not changing inside the truck. i just found out that my 4 wheel drive dont work. i looked at my vaccum lines and everything looks good. i too.k. them off and dont feel any suction. is it possible that my vaccum pump has gone bad? if so is it gonna hurt to drive it? and how hard is it to replace

I have never seen one go bad, seen them leak oil and a seal kit fixes that. there are two check valves in the vacuum harness, one of which could be bad. rotted rubber hoses are suspect as well. with that being said I guess there is always a first time to see one fail. As far as replacing, it is connected to the power steering pump, they have to come out as one unit( I have removed them seperate before and it was a pain in the arse) . once they are out it is a piece of cake. Also some trucks have a vacuum resevior under the wiper cowl, I seen then crack and cause a loss of vaccuum. HTH