3G 4WD: Hubs lock or stay locked?

Question - I've been given conflicting answers to this.

I came up driving off road when all trucks had manual locking hubs. This meant that in 2WD your wheels were free spinning and did not turn the axles or differential. When you wanted to go into 4WD, you put the truck in 4WD and hopped out to twist lock the hubs to get the axle to engage the wheels.

Then in the late 80's this gave way to shift on the fly 4WD for people who were apparently surprised that they were all of the sudden off road and couldn't be bothered to lock their hubs. But this meant the hubs were perpetually locked and turning that drive line 100% of the time.

This causes:
Poor Fuel Economy
Excessive Wear
Increased Maintenance

So they started coming up with Automatic locking hubs where the wheels would be free spinning in 2WD but then lock the hubs in 4WD. But that was unreliable and had issues.

Now all trucks are shift on the fly and no one locks hubs.

So what system are we using now? Auto locking hubs? Always locked hubs? What kind of pixie dust is the system using?

 

Disconnects. One for the transfer case and one in the front pumpkin. Everything spins but the wheels are not connected to the transfer case. Motors do the manual job of moving them.

Personally, I'd still have Warn locking hubs and a lever on the T case but I'm the minority because I'm old and learned to lock the front hubs before I ventured out in crappy weather or on trails where 4wd may be needed.

 

Automatic locking hubs are not that common, the only one that comes to my mind is the IWE on the F-150, where they use vacuum to disengage the hubs for 2WD and then default is 4WD mode where things are engaged. F-150 still uses those. I don’t know of anyone else but I don’t follow GM so maybe they use something similar.

Toyotas typically have the ADD if they have part time 4WD. The ADD means the CVs spin since they are fixed to the wheel through the unit bearing, but due to the ADD in the right side axle tube disengaging the right side shaft, wheelspin doesn’t turn the ring gear, which means only the diff spider & side gears spin in 2WD. This is why 4WD shifts can sometimes take 5 seconds or more, because the transfer case engages first, and then the ADD still has to move the collar over for torque to go to the wheels. The light doesn’t turn solid until both have done their thing.

The deletion of manual hubs was mostly a convenience thing for the modern world. Honestly, I think the cons of the fully live front diff are way overstated. The “wear” occurring will be from u-joints that last a very long time and from lubricated internal diff parts. Your rear diff is spinning all the time already and it is under power and it’s still not wearing out. The front diff spinning under load would be just fine. The mpg is overstated as well, as it doesn’t take much mpg-sucking power to turn a front driveshaft. The maintenance might be a factor; you might want to change the fluid more often, but I’d say 50K is a safe choice which isn’t exactly frequent for most people.

There are downsides to the parts sitting still all the time also. A pinion seal could run dry and stick to the shaft when not in use. Then you go to shift and all of a sudden the shaft starts spinning at 3500 rpm and rips a chunk of rubber off the seal. That isn’t exactly ideal. That’s one of the reasons Toyota wants you to use the system monthly, to keep things in check.

If parts had continued to move all the time, there would never be a need to do anything other than change oils. Even then, spinning at no load, the oil barely wears out. So you’re still probably changing it about as often as a diff that only operates in 4wd.

The only benefit I see to manual hubs is easy 2Lo. I personally would leave the hubs locked for normal use and then disengage them if I wanted to manipulate for 2Lo.

I don’t see any benefit to the ADD personally.


TL;DR - CV axles spin all the time due to not having locking hubs. The diff ring and pinion do not spin due to the ADD motor disengaging the right side axle when in 2WD. This causes the front driveshaft to not spin.

 

Most vehicles now use unitbearings. This is the hub and bearing all in one. Only disconnect is at the transfer case. There are still some trucks using an axle disconnect. But with IFS and CV axles the hubs are always live. (Edit: see post below this one, I stand corrected) Wear when not engaged is negligeable.

From a maintenance and service standpoint unit bearings are so much easier and typically last longer than old school locking hubs and bearings. They also make it a super convenient place for wheel speed sensors for ABS and traction control.

the only downside is now a days you don’t get to see hubs explode and shoot across the trail

 

That’s all true on other vehicle, but Tacomas (and most all part-time 4WD Toyotas) have the ADD that keeps the front driveshaft from spinning. It’s the same concept as the 2018+ Wranglers and Gladiators, the 90s Cherokee’s and Wranglers, and the 90-early 00 Dodges. All of those had/have right side axle disconnects. And all of them can be problematic.

 

That was fun! On the plus side, that was a cheap fuse and you could be back on the trail in about a beers time, a couple tools, and some ribbing from friends if you carried a spare.

Now a AMC 20 axle..............Bwa HAHAHAHAHA!!!!!

I even tossed Mile Markers on my 95 ADD F150, maybe an hour, 100% reliable unlike the Ford system, and never had an issue for I think, maybe a ben franklin at the time.

 

Thanks. I didn’t realize the Tacoma had the ADD. As you said though, all else holds true. No hub lock other than the wheel hub/unit bearing that is always live.

 

The last truck I owned that had auto hubs was a 2000 frontier. I trashed those suckers. I wound up swapping in a pair of warn manual lockers that were bulletproof.

 

True. I got pretty quick at changing out shafts on the trail though. Then I switched to a properly sized axle and RCVs and never had to worry about it.

but yes, a hub was a far cheaper and faster fuse than specially on a Dana axle.

 

110% SAME!
I was always shocked that they started marketing 4WD to people who were like "WHOOOAAA - How did this happen? I'm off road?" I have always known to lock the hubs before heading out. And the obligatory backing up 12 feet after unlocking them.

 

Ford is the only one I know of that still uses locking hubs on the F150 and Super Duty but they have always been quite problematic on both platforms.

The F150 switched from vacuum to electronic locking hubs in 21, Super Duty as far as I know still uses vacuum.

Everyone else I'm aware of uses an ADD other than the Ram HD trucks that leave the axle live all the time.

 

https://www.tacomaworld.com/threads/free-wheel-manual-hubs-conversion.513930/

 

20 minutes and you'll see it all in action.