Rear Diff. always engaged when 4wd is on - Page 2 - Diesel Forum - TheDieselStop.com
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6.7L Power Stroke Engine and Drivetrain Discussion of the 6.7L Power Stroke diesel engine and drivetrain in the 2011-Up Super Duty trucks. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 6.7L Power Stroke engine.

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Old 12-24-2011, 12:57 PM   #16 (permalink)
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Here's my opinion: When in 4wd all 4 wheels will spin a the same speed, when going straight and traction is same for both tires on EITHER the front or rear axle. This is normal for a transfer case locked front to back(no center diff). If you have 1 wheel spinning faster on 1 axle, you will also have 1 wheel spinning faster on the other axle. When making a turn the outside front wheel is rotating faster than the inside front wheel -even though neither tire is slipping. Because 1 wheel on the front axle is spinning faster than the other, one of the rear wheels will spin faster also. Since the front end is heavier than the back end there will be more traction on the front tires forcing the rear tire with the least traction to match the front. Want both rear tires to spin at the same rate? Lock the locker and watch one of the front tires slide when making a turn!
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Old 12-24-2011, 04:35 PM   #17 (permalink)
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I think ol' Diablo has it nailed. After thinking about it, this makes perfect sense because the inner tire always has less weight on it due to centrifugal force/body roll. Its the one thats going to spin. Also, the rear axle is seeing a smaller radius turn than the front so when in 4WD something has to give, and its the inside rear tire. I don't think you have a thing wrong with your truck. As soon as I get a chance I'm going to go play with mine and see what it does. Its funny that I've never noticed this before but its entirely logical. --- Good shootin' Tex !!
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Old 12-24-2011, 04:47 PM   #18 (permalink)
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it happens in my truck as well, but i dont have anywhere near a new one haha. its because of the limited slip
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Old 12-25-2011, 07:22 AM   #19 (permalink)
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Quote:
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I think I remember reading in my manual somewhere that when in 4WD, the E-locker is engaged.
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You guys aren't reading the book carefully enough. It says that the E-lock (on both 2and4 wheel drive models) will automatically disengage above 25mph and re-engege below 25. You're missing the fact that it must be turned on before any of this can happen. There is no way on earth that Ford would design this thing to always be on below 25. You wouldn't be able to steer the truck on slick surfaces. *** P.S. In my book it's page 276. --- Read it again. If this guys rear diff is actually locking automatically when in 4WD without being commanded, he has a problem, probably the switch. Now, after all this having been said, a 4WD truck will hop and buck like crazy when turned tight on hard ground when 4WD is engaged and begs the question "why are you doing this in the first place?". I have to wonder if the driver is mistaking this binding effect for the rear end being locked. Just don't do too much of this tight turn/hard ground stuff because it's a good way to break the U-joints in the front axle. ----EDIT--- vtboy51, we must have been typing at the same time.

After reading it again I stand corrected, it must be manually engaged.
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Old 12-25-2011, 01:47 PM   #20 (permalink)
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Originally Posted by diablo53 View Post
Here's my opinion: When in 4wd all 4 wheels will spin a the same speed, when going straight and traction is same for both tires on EITHER the front or rear axle. This is normal for a transfer case locked front to back(no center diff). If you have 1 wheel spinning faster on 1 axle, you will also have 1 wheel spinning faster on the other axle. When making a turn the outside front wheel is rotating faster than the inside front wheel -even though neither tire is slipping. Because 1 wheel on the front axle is spinning faster than the other, one of the rear wheels will spin faster also. Since the front end is heavier than the back end there will be more traction on the front tires forcing the rear tire with the least traction to match the front. Want both rear tires to spin at the same rate? Lock the locker and watch one of the front tires slide when making a turn!

I think your a little off. When the transfer case is locked, the front and rear driveshafts will turn at the same rate because of the lack of a differential in the transfer case. There are to many variables to say that one wheel will spin the same as another front to back. What may be percieved as the rear locking up could very well be the binding in the front end with the 4x4 engaged. It has nothing to do with the differential in the front... it is an open diff. It is the u-joints binding that cause the front end to buck when on pavement, turning, in 4x4.
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Old 12-25-2011, 06:42 PM   #21 (permalink)
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Something does not ring true. I haven't been under the truck lately, but if the correct plug to Locker has been pulled (I don't know if there are separate plugs for the VS and Locker or not) then selecting 4 wheel drive or not CAN NOT make any difference. On the older trucks, the vacuum relay use to be on the pax fender. It is not there on this truck. If you can find that and unplug it, that will take the crow hopping out of the equation.
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Old 12-25-2011, 11:48 PM   #22 (permalink)
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The point in pulling the ELD plug was to eliminate the possibility of the rear diff. inadvertantly locking when going into 4WD- it was originally suspected that the selector switch might have been faulty, causing this to happen. As to the phenomenon of the inner rear wheel spinning, when making a tight turn (any turn actually) the rear axle follows a smaller radius than the front. The longer the wheelbase the greater the radius difference. Since both driveshafts are obviously turning the same speed, either the rear is going to spin a bit or the front is going to drag. Because the front has more weight and therefore more traction, its the one thats going to 'set the pace' for lack of a better term. The rear axle is the one thats going to "give", and since were dealing with an open diff., the tire with the least traction is going to spin. This is going to be the inside tire due to the aforementioned reasons of centrifugal force/body roll. The weight-and hence the traction-is going to go to the outside tire. I tried this experiment with my truck today and guess what, -- it did the same thing.
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Old 12-26-2011, 01:46 PM   #23 (permalink)
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How about jacking the rear end up off the ground and seeing if you can spin one tire without spinning the other one... I know if you are "locked" you can't do it. In a traditional, non-posi setup the other tire will turn the opposite direction. Not sure if this rear-end is setup that way or not.

If the OP hasn't figured it out by now, just send me a DM and I will jack mine up and help troubleshoot it for you.
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