2017 Superduty locking hubs?
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Mountain Pass
Joined: Nov 2019
Posts: 178
Likes: 60
2017 Superduty locking hubs?
Can someone explain to me the point of having the external locking hubs on my F350 superduty. I can still use the 4 wheel drive without having to get out and engage them, so why do I have to get out and engage them?
Fleet Mechanic
Joined: Jul 2019
Posts: 1,648
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I assume the hub dial positions on your truck are marked auto and manual. In auto the hubs will lock when you shift into 4 wheel drive using the electronic shift on the fly ****. In the event the auto locking mechanism does not work you can lock the hubs manually by twisting the hub **** to manual.
Mountain Pass
Joined: Mar 2004
Posts: 170
Likes: 12
Agree, and with the Shift On The Fly being vacuum operated, it can fail, so it's nice to have an alternative to engage them. It's one of those 'better to have it and not need it vs. need it and not have it available' options, in my opinion.
Cargo Master
Joined: Feb 2017
Posts: 2,428
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From: Wisconsin
has anyone shifted into 4wd at highway speeds with the hubs in auto, or must you stop first, then shift? I keep mine locked for the entire winter and shift (into 4x4) as needed, fast or slow, been doing this for decades with other trucks.
Fleet Mechanic
Joined: May 2017
Posts: 1,382
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I have used the auto feature at speeds of 50mph with no problems, either in or out of 4wd. I do let my foot come off the pedal when I turn the dial.
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Cargo Master
Joined: Feb 2017
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From: Wisconsin
OK, I'm with you guys on shifting at speed, but how does everything engage if the front driveshaft, axle shafts are not rotating the same rpm as the rear axle? What prevents the grinding (if any)? The front wheels are spinning the same as the rear, but the driveshafts are not, hmmmm.
Hotshot
Joined: Jun 2003
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From: SW VA
Postmaster
Joined: Jan 2019
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If I remember correctly, you are right
Laughing Gas
Joined: Sep 2017
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From: Southwestern Pa.
I have my doubts as to there being a clutch type device in the transfer case to ward off "carnage" in the hub area during engagement. It's likely there to smooth out engagement with the transmission. If you think about this, if you're spinning the rear wheels and attempt to engage 4wd, that's the only way/time that there can be a disparity between front and rear wheel speed, which might result in any "carnage". At all other times, front and rear wheels speed is the same. If you're stopped and try to engage 4wd, sometimes the splines in the hub/on the axle may not initially be lined up and engagement may require that the truck move a bit so that they do. This is why locking the hubs before actually needing 4wd is a fail safe method if you're one who doesn't engage 4wd until stuck and stopped.
Hotshot
Joined: Jun 2003
Posts: 12,341
Likes: 4,366
From: SW VA
I have my doubts as to there being a clutch type device in the transfer case to ward off "carnage" in the hub area during engagement. It's likely there to smooth out engagement with the transmission. If you think about this, if you're spinning the rear wheels and attempt to engage 4wd, that's the only way/time that there can be a disparity between front and rear wheel speed, which might result in any "carnage". At all other times, front and rear wheels speed is the same. If you're stopped and try to engage 4wd, sometimes the splines in the hub/on the axle may not initially be lined up and engagement may require that the truck move a bit so that they do. This is why locking the hubs before actually needing 4wd is a fail safe method if you're one who doesn't engage 4wd until stuck and stopped.
The T-case is bolted to the transmission, with a solid, splined shaft connecting them. There is no clutch between them at all. Inside the T-case, a chain directs power from the main shaft, down to the front output shaft. This is where the clutch is. The clutch spins up the front driveshaft and axleshafts to match the tire speed. Since the hubs are connected to the tires via the wheel hub, the axleshafts HAVE to match the tire/hub speed before they will engage. You CANNOT engage the hubs before the t-case is locked in 4WD (while moving). You cannot engage two steel gears or splined shafts moving at different speeds, without bringing them both to the same speed (ex: floating gears in a manual transmission)
7289 is the fork that engages the clutch hub (7F063) to spin the front driveshaft up to speed.
