There are times that I'm on a hard surface in my '04 FX4 and I want the slow speed and throttle control of low range but I don't want 4WD because it will put the drivetrain in a bind. Mainly trailer-spotting on a slope, or in tight quarters.

I think if I put a switch on the dash that energizes the relay that disconnects the front hubs, that should give me what I want. Has anyone done this, do any electrical gurus have any hints, and do any driveline experts see any downside? I think my front driveshaft and axles would just spin like having manual hubs disconnected.

I'm thinking I'll put a switch next to the lighter, with an "on" indicator so I don't run around town with it engaged accidentally. From what I read in other posts I think I'll have to send power to the relay, since the hubs are engaged when the truck is off.

Thanks for the help -

- Lee F.

PS - where IS that front hub relay, anyway?

 

I think I found the relay on the firewall on the passenger side. Does it only work the hub vacuum or does it do anything on the transfer case as well?

I've heard that it's fail-safe to 4WD, so if vacuum is lost the hubs engage. I also have heard that the relay always has power and the PCM grounds it to "turn it on" - does grounding it make the hubs engage or disengage?

I'm confused . . . . . anyone know how this thing works?

- Lee F.

 

You already have a low range in 2wd, it's called first gear. Shift the tranny down into "1" and there's your low range. This is what happens when you shift into 4low, the front diff gets it's power through gears connected to the rear drive line. The PCM then keeps the tranny in first to get the torque and prevent you from driving too fast in low range (10 MPH max I believe). Shift it into first and get on the throttle, it's just like being in 4low but without the binding.

 

Tbird69, are you saying that Ford no longer puts low range in their trucks? My F150 is two wheel drive, but the almost two dozen 4x4 vehicles that I have owned in the last thirty five years have all had low range. Which is not the same thing as low gear in any sense.
Chris

 

The F150 does have low range, and it is not the same as what Tbird is mentioning. It is the same as low range on every other 4x4 vehicle. The throttle control is different in low range as well to keep the truck from feeling so "jumpy".

I agree that a 4x2 low would be ideal for moving my travel trailer around. I use 4 low in my gravel driveway, but not at the paved campgrounds.

 

It's not a question of using first gear. 4WD trucks have a 2.64:1 gear reduction built into the transfer case, so in 4 Low, EVERY gear, including first and reverse, is 2.64 times lower than in 4 High. That gives you 2.64 times the torque at any RPMs including at idle. It's nice to be able to quietly push your camping trailer into its spot on a slope without a whole lot of engine revving if there are other campers around, and you can move the truck a fraction of an inch at a time when positioning to connect the trailer. It's just a whole new level of control that's there for the using except if you are on a hard surface and have to do a lot of turning - then drivetrain bind gets to be an issue.

I think if I put a switch in the hot lead to the solenoid, then when I open the switch, the hubs will stay disconnected - just like pulling the plug on the solenoid (which I will try when it's not pouring rain!). If I do put in a switch, I'll probably also set it up to light an idiot light when the hubs are unlocked. I don't think I can use a switch with a built in light because it needs to light when the power is off. I think it will take a DPST switch, if I can find a nice one of those in a rocker style.

 

I know that the Low 2WD mod can and has been done on the F250's with the ESOF. Simply snip a wire and install a switch.

When you figure out how to do it to the F150 please lets us know. Pics are always nice.

 

Thanks for the info, Neil -

Looks like I'll have to give it a try myself! I'll do the unplug thing first to make sure it doesn't cause the PCM to throw a CEL or create some other mischief.

 

I wasn't trying to misinform, this is the way I do low gear in 2wd when I need it but can't use 4low (because I need to make a tight turn to complete the pull for example). If I can pull in a straight line I use 4low, eg. pulling a boat out of water up a launch ramp.

If I misinformed on any level I apologize.

 

OK - results of "test #1":

1 - With the truck off, the hubs are locked (as expected - no vacuum).

2 - With the truck running and in 2WD, the hubs are unlocked (again, as expected).

3 - With the truck running and in 4 LOW, the hubs are locked (once more, as expected).

4 - With the truck running and in 2WD or 4WD, with the connector unplugged, the hubs are LOCKED.

Next step will be to test voltages in the different conditions - the schematic I've seen makes it look like the solenoid has voltage at all times, and the PCM grounds it - I was hoping it would ground it to lock the hubs, but now I'm betting it grounds it to unlock them. Probably a fail-into-lock mode, similar to if you lose vacuum.

As a side note - when the solenoid connector is unplugged the 4WD HIGH light never comes on, but the truck seems to go into 4WD HIGH. The 4WD LOW light does come on, however, and it is in 4WD LOW. So if your 4WD HIGH light isn't coming on for some reason, check that connector.

 

Alright, I have your answer to this. Under your hood you will see the solenoid towards the back rear of your firewall on the passenger side. It's a small black tubular gagdet. It's mounted to the wall near the top corner. That box is the solenoid and either engages or disengages your vacuum hubs. Mine keeps grounding itself out and blowing the fuse to it so I've had to deal with this part dozens of times. I've had to rig the vacuum lines for them to work a few times while I was doing my fabtech lift as well. Find out which wire is hot out of the two going to the plug (pull out the electrical connection on top of solenoid, there will be 2 vacuum hoses connected to it below the electrical connect.), it will only be hot while in 2wd and the vehicle is on or set to run. Then obviously just run a switch to that line and another hot source. Now you can engage or disengage your hubs while in 4wd and 2wd. Hope this helps. That solenoid is about $55 from the dealer.

You can also go another [easier] route and bypass the solenoid by disconnecting the hoses that are attached to the solenoid, then connect those two hoses with an intermediate piece of hose with couplers on each end of the intermediate hose, then you have constant pressure (therefore hubs are disengaged all the time) or until you just crimp the line or even better, pull the intermediate hose off one end, then they're engaged. It's very easy and had to do this myself for a while until I could diagnose a problem I was having. If any of you can help me with my consant blown 4x4 solenoid fuse I'd appreciate it, I can't figure out where it's grounding itself.

And Lee F. you are very right, I was having that issue and it's either the fuse or the connection, usually the fuse as it was for me.

 

Looks like one leg is hot all the time (even with the truck off) and the other leg is connected to ground when it's in 2WD, which energizes the solenoid, sending vacuum to the hubs and unlocking them. So if power fails (like a blown fuse in Josiah's case), the solenoid de-energizes, vacuum goes to the hubs, and the hubs will lock. Looks like all I have to do is cut into the wire on the "downstream" side of the solenoid and put my own switch to ground in place. Anyone know where to get a nice looking three-way rocker switch without a "center off" position? That would do the trick.

I found the schematic diagram for it, which seems to agree with what I found on the truck. I'd post it, but I don't know how to add a picture yet.

If I could get a connector like the Ford one I could try it out without cutting the wire - are they available from a dealer or elsewhere?

 

Take a look at the switches that this individual has available. SWITCHES I bought several from him for my mods on my F250. You can contact him via email at
roan65@yahoo.com

 

Thanks for the switch info, Neil. I'm thinking I can put the switch in the panel next to the cigarette lighter.