LariatDude

Oh my bad yeah, it was a misread. Nonetheless at least that gets ruled out. But yes, you should be able to blow through the white end, but not the black. The black allows the engine to suck air through it to provide vacuum but in case a loss in engine vacuum occurs, the check valves are one of the first lines of defense to prevent the hubs from engaging. The valves are identical yes. When you went back into 2WD and noticed no noise again, did you put a load on the engine like on a hill? Often times I could barely replicate the condition on a flat road here in Florida. However, we have a few nice big steep grade causeways that connect the mainland to beachside. Every time I'd hit that causeway, the load made the hubs lose vacuum. So far we're doing well with diagnosing the checkvalves. But then we'll need to start focusing on the IWE system which is a bit more pricey. BUT as with mine: if one IWE hub loses vacuum under load, it takes the other side down with it. It's all a closed system, and leak points compromise that vacuum. If we get to that point, like someone said up top just buy a cheap Harbor Freight vacuum pump with a gauge and you can test the IWE hubs later yourself if you so wish.

northern pointer

I took the truck up a fairly steep hill in 2x4 and there was no noise after doing the switch to and from 4X4. However, when I got to the bottom of the hill and stopped, the noise was back when I started moving again. I've changed two of the check valves....the one closest to the solenoid, and the next one about a foot away. However, the third one near the brake booster has a wider diameter on the white nipple side, and when trying to get a replacement at the dealership, they are not available on their own, unless you buy it with the hose that connects to the brake booster and pipe. I blew into that third check valve and seems to be working, as air flows only from the white side. As for a Harbor Freight vacuum pump, they are not available here in my hometown in Canada. Even Amazon doesn't seem to carry them. Will have to look for another brand I guess. I think it's off to my mechanic in the next few days. Hopefully I haven't worn out the gear in the wheel.

HeathMc

A vacuum pump is almost a must while trying to diagnose this problem. Have you tried looking for a break bleeding pump? It's labeled as both a vacuum/break bleeding pump. But throwing parts at it is really not the answer. Would a parts house up there by any chance rent you one with the rent a tool program? Could be a pinhole in a line you can't see. Good luck!

LariatDude

That^.

And Don’t worry about the teeth on the axle, they’re heat treated and hardened. Yes it’ll wear down as the hub chews into it but you could run it grinding for a few days no problem. Mechanic would be the easier solution for sure if you’d like that route!! However we’re here for you if you need any additional help 😎!

northern pointer

Thanks so much. I appreciate it very much. Have been looking for a vacuum pump locally and found one at two different stores, priced at $79.99 before taxes. And they do both pressure and brake bleed. May have to bite the bullet and get one. As for the gear grinding, it's been happening for a couple of weeks or so, thinking it might be broken baffles in the muffler, until I found out here that it's the 4x4 system. I believe one of the tire / parts stores does rent equipment, so I'll check with them. So don't know how much of the teeth have worn down. I'll get a pump for future use, but it looks like my mechanic will be seeing me soon. Will give him a call this coming week.

Thanks to all, especially you LariatDude, for your help.

northern pointer

Anyone know what the stock number is for the check valve nearest the brake booster? It's different from the other two closer to the solenoid in that both nipples are the same diameter. The other two have different nipple diameters. This valve is not available on its own. It has to come with the tube that attaches to the brake booster too, and cost on it is about $45 Canadian. I'm looking at a

ACDelco 14047619 GM Original Equipment Cruise Control Vacuum Harness Check Valve

ACDelco 14047619 GM Original Equipment Cruise Control Vacuum Harness Check Valve

as a possible replacement for $4.15US from amazon, with prime shipping. I know amazon says it doesn't fit my F150, but reading the reviews, lots of people have used it successfully on other vehicles besides GM and appliances. Don't know if it will do the job, but worth a try. Anyone familiar with this valve? But first, I'm going to check the vacuum pressure on the lines. Picking up a pump tomorrow.

HeathMc

Head to fordparts.com and throw your info it. Should find a diagram with the pet number that you are looking for.

starrman

I pull a travel trailer with my 2008 Lariat and under load (lugging the rig up a hill) I will get this rattle. I thought it was the power steering pump sucking air and it has been driving me nuts. I cant wait to see if it has been the vac leak all this time. My PCM crapped out and I'm looking for the rebuilt one to arrive tomorrow. THANKS FOR YOUR POST