The front end of my truck has started to make a noise comparable to running over the rumble strips on the side of the road (not nearly intense though). It only does it about half of the time. It will be running completely smooth, then I will hit a bump and it starts vibrating and making the noise. If I had to guess it feels like the front end is locking and unlocking? Also when I put it in 4wd the light turns on but I usually have to drive it 1/4 mile before the front tires will start turning. And the heater is stuck on defrost.

I am by no means a mechanic but these are all things controlled by vacuum right? It's getting worked on monday but just seein if it was a simple fix.

 

my heater is also stuck on defrost 98 12v so far i've lived with it but what 2 do?

 

I can live with the heater, just not the feeling that the front end is falling off the truck. I'm just hoping that all of the problems are related

 

my heater is kinda stuck on def too. If i play and play with it i can make is come out the vents. ( on a good day) i need to go through the vacuum system and see if there is a leak or something.... has anyone had this problem and solved it?

 

I got something going on with my vacuum for the defrost/recirc flapper, but thats the only thing acting up on my trucks vacuum, haven't had a chance to look at yet though.

 

The vacuum system is fairly simple on my 1997. One line coming off the vacuum pump (driver’s side, in front of the power steering pump which T’s off and services the vacuum powered components (CAD on front axel, cruise control, auto tranny, and HVAC, maybe others?). The lines continue up and across the firewall to the passenger side. The default position (no vacuum) for the HVAC stuff is defrost. The actuator that controls the defrost/vent/floor on my 1997 is right above the go pedal on the center hump. My vacuum check valve on the vacuum pump failed and flooded the lines with oil. I used a MityVac from Harbor Freight to test the vacuum system. The leak took out the vacuum actuator (they are rubber inside). I got a new check valve from Cummins ($18). DC wanted $118. I found a replacement actuator at a junk yard for $5. I blew electrical parts cleaner through the lines then flushed with air and put things back together. No problems since.

There is a diagnostic procedure in the 1997 service manual to help find a vacuum leak. Let me know if you need this.

T-Bone

 

There is a recall for the vacuum system, not sure if it applies to '97 though. What happens is oil can get in the vacuum lines and melt them. Recall adds a check valve and replaces all the lines.

 

you might check you track bar on the front end