I'm new to the site but found this website to have great information.
Can anyone explain to me what is happening when you put your truck in 4x4 hi/lo? Specifically I have a 2011 lariat ecoscrew with 3.73 ELD. When on pavement and I put it in 4x4 hi or lo and turn a corner you can here the inner wheels front and back skipping. It is my understanding that putting my truck in 4x4 only engages the front wheels but does not lock the rear diff. If this is the case then why does my inner rear tire hop/chirp? My inner front tire hops/chirps as well.

With this in mind what would be the purpose of locking my rear diff if it already is locked just engaging the 4x4? (I understand what the ELD does)

Oh and if I put it in 4x4 and pull the **** to lock the rear diff it sounds the same turning a corner (both front and rear tires hop/skip).

 

First of all, understand that the locking rear, and 4x4 are 2 unrelated things. putting the truck in 4x4 has nothing to do with locking the rear.


First, when travelling in a straight line in 4x4 or with the diff locked, or both, there will be no "binding" because all of your tires are turning at the same speed.


Now, realize that when going around a corner, all 4 of your tires need to turn at 4 different speeds, (your outer front tire being the fastest, and your inner rear being the slowest), because they are covering a different distance at a given speed.


Now, putting the truck in 4x4 literally locks the rear driveshaft to the front driveshaft, allowing them to turn at the same speed, AND ONLY THE SAME SPEED. So no differentiation between the front and rear axle speeds are allowed. That is the binding you feel. There is still a differentiation in speed allowed between the left and right tires, but not between front and rear axle.


As far as the rear locker, this locks both rear tires together and allows no differentiation between left and right tires. You'll feel binding, or one of the tires dragging, or screeching, depending on speed, when its locked.


Locking the rear axle, in addition to turning a corner in 4x4 will exacerbate the "binding".


To sum it up, going around a corner requires all 4 tires to turn at different speeds, and in 4x4, and/or with the differential locked, the drivetrain will not allow that to happen.


Just a note, to help you save your truck. That binding is very hard on your powertrain, and should be avoided when you can. If you have enough traction for that binding occur, there's a good chance you shouldn't be in 4x4 anyway. That's why they tell you not to use it on dry roads.
Hope that helps

 

Thanks for the reply. So I sat in my truck with a ford tech guy from a dealer and he couldn't explain this to me.

So the binding I'm feeling in 4x4 and not locking the rear diff is the difference between the front tires and rear tires as they are forced to rotate the same.


I understand that doing this on pavement is bad and have only done it 1 or 2 times to check to see if my ELD was working in 2wd and noticed the binding in 4x4.

 

You got it


Now... for your own information, this also explains the difference between 4WD and AWD. All-wheel-drive vehicles are able to run on all surfaces and make turns without binding because they have the same differentials in the front and rear axles that you have, AND a torque-biasing differential, or viscous clutch set-up in the transfer case allowing the front and rear axles to turn at different speeds, while applying torque to both.