So all good things must begin with the phrase "Watch this son..." I said as I pulled off the road into a field to show my son just how saturated with rain the grass was. I was going about 10 mph when I saw the ditch. Turned wheels to right only to start a slide and brakes did no good. We ran right into it! BAM - truck was still running but drivers front wheel was in ditch with Passenger front in grass. Sitting on the underside of the bumper. No way I was going to back out with the mud. I tried to enguage 4X4 but no luck (dash switch) and Praise God for my neighbor, who has learned not to ask what happened just to ask how he can help, who pulled me out in 30 seconds with a chain and a handshake.

That was about four weeks ago. Ever since the truck has had an extra nosie when you are outside listening to it. It sounds like passenger side of motor near front. I have determined it to be the vacum pump. It is a "whomp" "whomp" sound not the sound of anything hitting anything. All the controls for AC/heat work and vents change as the should. Wastegate still operates and has good vacum. The only thing I can see and or find not working is the 4X4 will not enguage. When you go to 4X4 high you can hear the transfer case make a light sounded click and when you switch to 4x4 low it makes a louder 'thunk" - which it has since I have owned it which is about 5 months. Visual inspection shows not other likely culprit other than the vacum pump. By the way the truck drives straight, stops straight and does not pull so that is a blessing. It was a shallow ditch. I had a friend who is a 20+ year mechanic and diesel guy listen to it and he pegged the vacum pump as the noise maker. He said not to worry about it for now unless the noise bothers me if everything is working OK.

My question is can the vacum pump not operating at 100% be a cause for the 4X$ not to enguage?

Thank you!

~GOD BLESS~

john

1997 K2500 Suburban. 6.5L with 212K miles. New relocated PMD on cooler and new 4" exhaust. Looks like about a 2" lift kit on truck. Fresh Oil change. Cleaned all the ground points around engine and frame.

 

check the hubs first... make sure your seals arent blown out.. but yes your vaccum pump can and will affect your 4x4, check your hoses, look for tears, rips, anything that looks loose. might be as simple as somethings not where its supposed to be.

 

I have had the Burb' up on ramps three times now looking and listening for anything that could have gone amiss after the ditch. I have to say that I am not 100% sure the 4X4 was workinh properly before the ditch as I am a recent owner of the truck (bought it in August 2012). I checked it then on a gravel driveway and definately heard the passenger front spin. I also have used once or twice at the shooting range but not tried the 4X4 in the last few months. I just know it would not engage while I was in the ditch and will not engage in any attempts since then. The dash light for 4X4 high blinks and does not go solid as it does for 4X2 and the same behavior for the 4X4 low switch position.

I see a wire coming from the hubs that is actually two wires. I traced them to the transfer case where they connect on a clip to a set of wires coming from the transfer case (I assume high and low range). All connections look good and none had an over amount of grime built up on them. The 4X4 switch is dash mounted not on the floor. All that to say I do not see how and where the vacum comes into play with the engagement of the 4X4 front. Can you please tell me how it works?

In all three inspections I did not see anything loose or knocked off other than on the vacum pump itself there looks like what was a 'cap' on the side of the canister that is now gone. I see it if I look at a new part but it looks like it was pressed in and on the new parts it is not a hose connection. I assume this is what is making the noise.

Any help is appreciated!

Thank you

~GOD BLESS~

john

97 Suburban 212K miles. 6.5L. Remote mounted new PMD on cooler. small lift kit (I did not install but about 2") New Ranchero shocks all the way around. New batteries. Fresh oil change. Lucas additavie in tranny.