Originally Posted by tjsfaith

Drove 30 miles rear end stop pulling as we are costing around 55 press throttle speed hand goes to 90 whats my problem

Originally Posted by VTX1800N1

Figured I'd post this as a reference so that I can avoid typing the same answer again and again when someone has a 4x4 problem and they don't know where to start.

First, a system description: On the 2004 (new body style) and up F-150 Ford went to a new design for the 4x4 system. Each front wheel has a vacuum actuator, called an Integrated Wheel End. These IWEs are bolted to the inside of the steering knuckle by 3 bolts, and a half-shaft (front axle) passes through each one into the hub, which is on the other side of the steering knuckle and secured with 4 large bolts. These IWEs (sometimes also called actuators) are controlled by vacuum. This vacuum comes from the engine.

When your engine is off, there is no vacuum supply. However, vacuum is still stored in a vacuum reservoir which is located behind the battery. This is possible because there are two check valves in the vacuum lines. One check valve is between the vacuum tap on the engine side and the IWE Solenoid, and the other is in this same line (T- fitting in between) between the IWE Solenoid and the vacuum reservoir. These are on the vacuum supply side of the solenoid. The vacuum control side of the solenoid goes directly to the IWEs.

Now, this stored vacuum is not used when the engine is off, because the IWE solenoid (located high on the firewall aft of the battery) is not energized, and so vents vacuum in the lines that go to the IWEs. The purpose of the check valves, then, is to ensure an adequate supply of vacuum to the system even when the driver commands full throttle, which would normally also deplete the engine vacuum supply. This will become important in diagnosis later on. With no vacuum to the IWE, a spring forces a geared locking collar outward onto the hub gear, which then locks the hub and half shaft together.

With the engine running, there is an ample vacuum supply. In 2WD, the IWE solenoid is energized (grounded by the 4x4 control module, actually) and supplies vacuum to the IWEs. A vacuum diaphragm in each IWE overcomes the spring that would otherwise force the locking collar onto the hub, pulling the locking collar in and off the hub gear, which lets the hub spin and the half shaft remain stationary, thus unlocking the front wheels.

Ford went to this "hub disconnect" system for a couple reasons. First, it prevents the half shafts, differential, spider gears, and front driveshaft from turning as you drive down the road in 2WD, unlike systems from GM and Chrysler that use a differential or half shaft (in the middle of the shaft) disconnect. This saves wear on all these parts. It also saves some fuel, especially in stop and go traffic, since you no longer have to spin all those heavy parts up every time you accelerate. Speaking of acceleration, turning all those heavy parts costs you performance, so it makes sense to avoid it if you can, which the Ford system does nicely.

In addition to the IWE disconnect, there is also a Transfer Case disconnect. Without getting into the specifics, Ford uses a clutch and magnet to engage or disengage the front driveshaft in the TC. A Transfer Case Motor is used to move the range select lever in the TC from 2WD to 4Hi to 4Low. The TCM is just there to perform the function of a floor shift level, basically.

So, in 2WD, nothing in the drivetrain (front driveshaft, differential, half shafts) spins at all. When you turn the ESOF switch to 4Hi, a couple things happen simultaneously. First, the TCM moves the lever in the TC to the 4Hi position. This engages the front driveshaft, with the internal TC clutch spinning it, the differential, and the half shafts up to speed very quickly. This is partly why your manual says you must be below 55 MPH to "Shift-On-the_Fly". That's a lot of mass to spin up in a very short time. Second, the IWE solenoid is de-engergized (no longer grounded by the 4x4 module). This vents vacuum from the IWEs. Their springs then force the locking collars onto the hub gears, locking the half shafts to the hubs and, by default, the front wheels. Thus, with the TC locking the front and rear driveshafts together and the IWEs locking the half shafts to the front hubs/wheels, you have 4WD. Now, the IWE and hub gears also have to mesh up very quickly, all while the half shafts are spinning up to speed- another reason Ford says this must happen below 55 MPH.

In order to get into 4Low, the truck must be below 3 MPH with the transmission in Neutral (not Park, it has to be Neutral) and the service (foot) brake applied. The TCM moves the TC lever again, which changes the gearing inside the TC and locks front and rear driveshafts into Low range.

Now, you will notice that from the IWE's perspective, engine off presents the same conditions as 4Hi and 4Low- that is there is no vacuum supply and thus the IWE locking collar springs lock the half shafts and hubs together. You should be able to test the signal to the IWE solenoid from the 4x4 control module with a digital volt meter. Unplug the electrical connector. In 2WD (and when the engine is running) there should be voltage across the wire harness side terminals. In either 4x4 mode or whenever the engine is off, no matter where the ESOF switch is, there should be no voltage there.

Further, each IWE has two vacuum line connections. There is a double rubber vacuum hose at each IWE. You cannot put the hose on wrong- one hose is larger than the other. The larger hose is the vacuum control line from the IWE solenoid, and the smaller hose is a vent line that runs up high in the engine compartment and is not connected to anything (hence, it is only a vent).

Originally Posted by Shaw72

I have a 2012 f-150 4x4 that I took to a mechanic BC I thought hub bearing went out in the passenger side front end, he also thought it was a hub bearing, so he replaces the bearing and I go to pick it up and test drive it and its still making the same noise, he starts to look for other culprits that could be a problem and finds the vacuum hose on drivers side had come off, could it be the actuator making the same hmming, grinding noise in the front end? And this is all in 2 wheel drive when making noise did not test in 4 wheel