I think I am on the right track here and I just wanted some reassurance that I am.

Recently I have noticed a loud buzzing noise from under the hood. Traced it down to the vacuum pump. It will cycle on nearly every time I am in wait to start mode. I have also started hearing a noise from my HVAC like a light shuddering noise when I am switching to different modes.

So far my 4 wheel drive had engaged every time I have asked of it, but I am thinking I have a slow leak causing the pump to cycle each time upon start up and the shuddering noise.

My guess like everyone else would be ESOF hubs right?

Thank you I just want to make sure I am on the right track.

If correct I will most likely be switching to some manual hubs and cap off the ESOF hubs.

Thank you all for any help or corrections.

9905

 

I can't help with the 4wd question, but in my situation on my 2WD, my pump would do the same as you described on wait to start, & it turned out the pump had come off the bracket. I got the rubber feet snapped back to the bracket, all's been quiet. I must of knocked it when I was under the hood tinker'n.

 

Mine will also turn on as I turn the key for wait to start, I will hear kick on as mine is somewhat loud. I have manual 4X4 locking hubs, non of that auto stuff. If your auto hubs are leaking it would be inside the wheel hub assembly, I think. I believe its a yellow pretty large in size o-ring, there is a whole write up of it some where on this forum. If it's working fine I wouldn't mess with it. As far as I know the only reason the diesels have vacuum pumps is for the heater/AC controls and the auto 4X4.

 

It would be normal for the pump to run on start up, the vacuum reservoir won't hold forever. As for the shuddering it could be the "door" dragging when switching from defrost to the vents for dash or floor.