It seems that with winter coming to most of us, there have been a lot of questions about the functionality of the vacuum-operated hubs many have on their ESOF 4x4s. It also seems that if they don’t work when you flip the ESOF switch, people call them POSs or worse. I’d like to set the record straight and show a bit about how they work and how to perform simple maintenance on them that should keep them operating whenever they are called upon. If others have more info or more detailed knowledge of their operation or modification, please post in this thread. Hopefully from here out when someone posts and says their hubs didn’t work we can just link this thread and answer the questions. Pics are linked at the bottom of the post.
This is all based off my experience and may not work on all vehicles. Perform at your own risk!
When you select 4HI on the ESOF switch, two main things happen. A motor on the transfer case engages the front drive shaft, and the hub vacuum solenoid applies vacuum to both front hubs. 4LO is the same except the transfer case motor engages the low range gears and front drive shaft. (Note you have to be in neutral or park with a foot on the brake to engage 4LO)
The vacuum solenoid stays energized for about 45 seconds. This pulse operates the auto hub, which is similar to a clicker-style ball point pen. The pulse is applied and released much like pushing the top of a pen – the tip stays out/the hubs stay locked. When you disengage, vacuum is applied again, the hubs unlock (push the pen top, the tip goes in). When you rotate the Auto-Lock selector to Lock, it is like holding down the button on a pen – it forces the hub to lock (pen tip out) continuously.
The key to getting the hub to engage is motion. While the transfer case will shift into 4 while stopped, the front wheels have to move in order to engage the hubs. If you are already stuck, the front wheels can’t spin, and the hubs can’t engage. If you need 4wd, engage it via the ESOF switch while the truck is in motion. If you are already stuck, rotate the Auto-Lock selector to Lock to force the hubs into Lock and you’re good to go.
A note about the Lock position: It IS NOT bad to drive around in 2HI with the front hubs locked. It causes the front differential and front drive shaft to spin, but the drive shaft is disconnected in the transfer case. You may see a little drop in fuel economy, and may hear the gear noise when turning, but it will not damage your rig. If it is snowy out or you anticipate needing 4wd, just lock the hubs before you leave. Then you don’t have to worry about any of this. Of course, leave them unlocked for a cross-country highway trip, but many people up north simply lock their hubs in the fall and unlock them again in the spring.
To verify if your hubs are locked there are several things you can do. The easiest is to verify that they are unlocked (2WD, hub in auto). Reach around the wheel and grab the U-joint in the steering knuckle. You should be able to rotate it by hand. Either the opposite side knuckle or the front drive shaft should also spin. Note the opposite knuckle will spin in the opposite direction. As a test, lock one of the hubs manually and then rotate the front drive shaft by hand. The unlocked side should spin freely (open differential). Once you are done using 4wd, go back to 2wd (motion is required again) and try to spin the knuckle. My hubs typically do not unlock automatically when going from 4wd to 2wd. After using 4, and when I no longer need it, I have to manually unlock the hubs (reset the ball-point pen). Rotate the selector to Lock and back to Auto once or twice and spin the knuckle again. They should now spin freely. You can play with the setup by safely jacking the front axle off the ground and with the key on (not running), put the tranny in neutral and select 4x4. Spin each of the front tires through a revolution or two within the 45 seconds of solenoid activation. You should feel each wheel engage and see the front drive shaft spin. Select 2wd, feel the hubs unlock once they are rotated.
You hear a lot about hub selectors that are too stiff to turn. If you maintain them properly (like any piece of equipment) a ten year old should be able to move them back and forth. Here’s what I do with every oil change. It takes all of ten minutes and requires no tools, and is virtually risk free (no bearings will fall out, etc).
Pictures are linked at the end of this post.
1. Remove the plasti-chrome lug nut cover/hubcap
2. look at the hub – there is a retaining ring with two prongs sticking out. Squeeze the prongs with your fingers and pull out the ring. If they are dirty, you may need some needle nose to get it out.
3. Now just pull the hub straight out. It may need a little wiggle, and really dirty ones may need a few gentle taps from a rubber mallet.
4. Clean the inside of the hub. Remove any grease. Inspect the O-ring seating surface and lock-ring groove
5. Clean the hub. Now is the time to soak it in penetrating oil if the selector is too stiff to move. Select the Auto and the Lock positions and spin the inner shaft – see how it works?
6. If you start removing the small lock rings on the hubs themselves you expose bearings – I personally don’t go any further.
7. Inspect the O-ring. This is what keeps the vacuum while locking.
8. I apply a light coat of waterproof synthetic grease to the metal surfaces and O-ring. Some say it is not necessary, so you’ll have to decide for yourself.
9. Now reassemble. Push the hub all the way back in and give it a little extra push at the end to make sure the O-ring is seated. Put the retaining ring back in – MAKE SURE it seats in the groove (so your hubs don’t pop off)
10. Verify they are back in Auto, and check to make sure the knuckles move freely
Some want the ability to use 2LO in certain circumstances (backing a trailer is one big one). There are a few ways to do it. One is to disable the vacuum function altogether (see next section)(least preferred method). The other is electronically (preferred method), All you have to do is wire a switch that prevents the hub vacuum solenoid from energizing when 4WD is selected (see pics at end of post) FOR MY TRUCK this worked: Cut the red wire going into the hub solenoid far enough down to splice into both sides of the wire. Run a new wire from one side of the cut to a switch on your dash, and then back to the other side of the cut wire. I mounted my switch so it is closed (on) in the down position. Thus, when it is down, everything acts like normal. When it is up (open), the hub solenoid does not engage, and the hubs do not lock. Now when you want 2LO, start in 2Hi with the hubs unlocked. Flip the switch up, place the ESOF switch in 4LO (remember, neutral, foot on brake), and viola! Now, to get 4WD back, either lock the hubs manually, or take the ESOF switch back to 2HI and your hub bypass switch back to off.
Some like to just remove the vacuum feature all together, and treat the hub like a conventional manual one. (not sure why, but more power to ya) If you want to do this it is not difficult. Look at the bottom o the vacuum solenoid – there is a red line that runs to the hubs and a black line that tees into the vacuum reservoir and then goes to the HVAC system. Plug the red one at the elbow further down the line and you’re set.
Please add to the thread if you have more info or if I am all backwards. Again, these work for me – no guarantees! Check out the pics – they should explain most of this.