ok I've been having ongoing issues with my 4wd. initially the shop I took it to replaced the actuators and it seemed to work then after a couple of months i started to hear a metal on metal screeching sound and the vacuum line just on the inside of the front tire had come disconnected and was causing the one hub to engage. this happened on both sides several times. I would put the line on and it would be fine. then one day 3 or 4 months after replacing the actuators the 4wd stopped working again so i went to the shop again and they said it was the solenoid so I replaced it and after that the 4wd worked fine a couple of times. then I went to use it and I turned the switch and waited a second for it to engage and then accelerated and all of a sudden CLUNK! and the 4wd was engaged. It did this for a couple of uses then quit altogether. So the other day I gave the solenoid a tap with a wrench and the 4wd started working, but today i went to use it driving down the highway and it would try to engage then disengage and made a kind of grinding sound. so I am at an impasse. obviously the mechanics cant figure out the problem so i wonder if anyone else has any ideas

 

the front hubs are unlocked by vacuum from the engine. when accelerating the vacuum drops. there is a one way check valve in vacuum line near solenoid that prevents vacuum drop from reaching wheel hubs and causing them to partially engage. very common for them to fail. it's a small plastic piece, black one one side and white on the other. cheap and easy. as far as loud clunking on 4x4 engament that is normal from the transfercase. just blow threw the check valve, it should only let air threw one way. if left to long it will take out the actuators.

 

so i pulled apart the check valve and i can blow thru it both ways so i guess ill go get a new one tomorrow thanks a bunch! hopefully this solves my issues!

 

alright. the check valve was screwed. so i put one in and drove it down the hiway. i switched to 4x4 and i heard this clunk.....clunk....clunk (an accurate description I know) it was like it was trying to engage but unable to do so. so i switched it off and returned home and here I sit. could it be that it has wreecked the actuators? I didnt hear any noise any time that would've indicated to me that the hubs had been partially engaged.

 

4x4 on pavement is not good for the 4WD driveline. Find a dirt road or grass area for your testing.

Read though this to see if you might have some other vacuum leak in the system.

http://www.ford-trucks.com/forums/836438-everything-you-wanted-to-know-about-the-iwe-system-and-then-some.html
A gentle "clunk" sound is normal when engaging the 4WD. Does your 4WD light come on (and stay on) when you engage the system?

 

yeah the light comes on and stays on. when i flip the switch, you can hear a click. i tried it on ice yesterday. I flipped the switch,waited a second for it to engage then gave it some gas and no 4wd. I gave it gas again and it started to spin in 2wd then it engaged and I had 4wd. This summer I had problems with the vacuum lines popping off where they attatch behind the front wheels. I replaced the solenoid and that issue seems to have stopped. I just took it down a dirt road, flipped the switch at about 35 mph and it clunked about every 5 seconds or so.

 

Could be redundant - but did you check the second check valve? Sits in-line where your vacuum line runs towards the back of the engine, above your right-side COP's.

 

I would recommend blowing out all the lines with brake cleaner, as it evaporates clean. If you ran for even a short while with the vac line disconnected from your IWE's, then their would have pulled lots of nice dust and crud into the system. I had a blockage in both check valves and at the T above the right wheel where the line branches over to the drivers-side. Disconnected all the lines, shot them with brake cleaner, and blew them out with 30-40psi. Amazing how dirty the lines were. Was able to clean out the check valves as opposed to replacing them a just soaked them in some cleaner and gave them a LIGHT blow-out.

 

Check the vacuum system/parts per the previous link. This sounds like a classic "mystery vacuum leak" issue.