There have been a few threads from guys that have blown up transfer cases. I think the common theme was driving high speed 65-75 on the highway on dry pavement with 4H engaged. I also think it was older trucks (05-08 -ish era). But there haven't been that many.

I try not to engage or disengage mine at highway speed, and I always lift my foot all the way off the gas first, to take any torque load off the driveline. And I don't engage or disengage while turning. Occasionally I'll hear a "clunk", but not most of the time.

 

I try to engage and disengage under the same situations as you. When I heard the clunk I was stuck and blocking a travel lane with an oncoming vehicle. I shifted to 4H with torque on the drivetrain. Didn't like that sound.

 

The tcase is the strongest avalible in these trucks. Also remember the blowing up tcase issue could be lack of maintenance, driveline vibration etc. Not just being in 4wd at high speed.

 

I'm old school, I like the manual hubs. In the winter I leave the hubs locked in and shift in and out of 4WD H as I feel it's needed. Even when I have the plow on, I'm in 2WD when just driving. I will also agree that being in 4WD definitely helps the "whoa" in some case - having the engine braking apply to all four wheels can definitely be helpful.

 

This was something I wanted to understand more. The manual hubs. I see I have them on my truck still, but obviously have the switch too. How are the two related? I assumed the manual hub locks where there in case the electronic switch malfunctioned or something. Is that not it?

 

I obviously don't drive the newer trucks, but I believe the switch actuates a vacuum pump to engage or disengage the hubs. The manual hubs are a failsafe in the event that the vacuum system malfunctions, you'll still be able to use 4WD by manually engaging it.

 

Hmmm, guess I'm not much help there - I've never had a truck that had both manual hubs and an auto system.

 

The hubs on the newer trucks select between Auto and Manual. No reason to lock the hubs in, they engage with either the turn of the ****, or the pull of the lever, whichever your truck has.

The new trucks do have manual hubs, but you manually select between auto and engaged. Back in the day, manual hubs selected between locked and unlocked.

 

My 2000 does... but I'm sure it's different system than the newer trucks.

The hubs can engage one of two ways. There's a diaphragm inside the hub and when vacuum applies to it, it sucks the collar into the gears and locks the hub. If you turn the ****, it pushes the collar into the gears and does the same thing. It's a very clever design. I have mine apart right now to clean and re-lube and I've been playing with the parts until my bearings and seals get here.

Again, this is how the hubs on my 2000 work.

 

So kind of what I said. The manual option on the hub is there in case the switch fails (or they don't engage for some reason). Once you engage at the wheel hub itself, the switch is useless, as you are in 4WD. Right?

 

On mine, the switch controls the transfer case shifting as well.

 

No, transfer case only engages with the switch. Auto position on hubs works off vacuum when you turn the switch to 4wd. If the vacuum system fails, then manual position on hubs will lock the hubs, and Your front axels and driveshaft will turn with the tires, but no power will be applied from the transfer case until you turn the switch on dash to 4wd.

 

Ah, good to know, thanks. I never really liked the vacuum/fully auto ones, sounds like the newer ones are the best of both worlds.

 

I'm interested in how other people use their trucks and their results from how they use them. personally I use my 06 F350's 4x4 literally every day multiple times a day on the farm. The auto hubs have been locked manually for going on 7 years now, I forget to shut the 4x4 off occasionally and have driven on pavement and at 125k nothing other than greasing the knuckle u-joints has been touched or a problem.... My former truck was an 94 F150 used in the same manner and also never had any problems at 190k.

I locked my hubs in permanently because I hated the engagement clunk and also when I want 4x4 I want it NOW!

 

With the standard open front diff, your main concern, on dry pavement is a tight turn with heavy throttle, because each front wheel wants to turn different speeds (the open front diff allows this), but NOT necessarily the same speed as the rear tires. The transfer case is a direct connection between the front and rear driveshafts, even when coasting, and in tight turns the front tires are being driven via the front driveshaft at the same speed as the rear tires/drive shaft.
Sudden changes in traction for 1 or more tires, under heavy throttle (or engine braking, down shifting) is when things will break, often it is the weakest link that fails.

With manual 4wd,
Manually locking a hub, simply connects that hub to it's front axle half, you are NOT in 4wd UNLESS you engage 4wd via the manual 4wd floor shift.

With ESOF, you can manually lock/unlock** the front hubs the same as above.
When you select 4wd on the ESOF, it will put transfer case into 4wd, PLUS it will attempt to lock the front hubs via a vacuum activated mechanism, IF necessary.

** I don't think you can manually UNlock them, if the ESOF system is in 4wd and is properly working.

The vacuum line is a common fault and effects the locking of 1 or both front hubs, hence folks will manually lock the front hubs (just in case), or go with manual 4wd floor shift vs ESOF.

The manual 4wd floor shifter allows 2wd LO, by simply leaving the front hubs UNlocked with the floor shifter in 4-lo.

Driving around in 2WD, with front hubs locked, just adds rolling resistance and decreases fuel mileage, since each tire is now spinning it's front axle half and the front driveshaft. It also adds wear to the components, and can cause binding in the rotating "joint" in the connected front axle half.