I have a 1998 2500 and I have been having 4 wheel drive issues. We changed all the lines and everything is new, but the vac doesnt seem to work still. Is there any way to test the vac to see if it is bad, or what should i do? Thank you

 

get what they call a mity vac it is a hand operated pump you can apply vaccum with itwill also allow you to see if you are getting vaccum to the switch also u can check the switch for proper operation good luuck and hope this helps

 

and you can also crawl under the truck and check for vacuum while someone else engages 4wd. be careful. you have do do it while its running.

 

if you find you are getting vaccum and your acuator is working then check the u joints. also try taking the accuator of spray wd40 in both sides of the diaphram and then work it back and forth slowly. they have a tendecy to build condesation and then rust.<-- happened to my dad three times

 

ok i will try all that, thank you guys very much