4WD explanation please:

[CVsGX470]

Hey all...quick question regarding 4WD.

What is the difference between just 4WD and "Locking the Differential?" Besides the obvious handling feeling.

If I put my runner into 4WD to lube up the system, it feels no different than if it was in 2WD. However when I put my father's Tacoma into 4WD it feels like when I lock my differential. My wife's liberty feels the same way. It almost feels as if the truck wants to stop as you make a slow turn on dry pavement. Can anyone explain the difference?

And why would you want to lock the differential vs just 4WD?

Thanks,
CV

 

[sharp4runr]

When you lock the center differential it applies power 50/50 to the front/rear equally.

4WD drives all 4 wheels but power is variably applied where needed.

You would want to lock the center diff in 4WD if you do not want VSC kicking in to stop wheelspin. If you are going through a mud pit you want power going to all wheels without VSC limiting power from the front or back wheels because of tire spin. ATRAC will still activate, but NOT VSC.

I don't know the 4WD systems of the other vehicles, so its possible that they do not have an active center differential like the 4runner.

Someone feel free to correct any of my statements or add on to it...

 

[Thai]

Your Tacoma has part-time 4wd system. Therefore, when you put it into 4wd, the front and rear axles are locked together. When you turn a corner, you feel "binding" because the front axle wheels are turning at a different rate than the rear wheels. The only way to prevent binding is to allow the wheel(s) to slip...thus, you should only do this on dirt/wet roads.

In your 4runner, you have a center differential that allows for differential in speed between your front and rear axles, yet still be in 4wd...to prevent binding. Thus, you can turn the corner on dry land without destroying your differential.

Now, if you lock the center diff on your 4runner (effectively locking the front and rear axles together), then you would have the same binding effect as the Tacoma.

With the Liberty, if you do not have Select-Trac, then you have the same system as the Tacoma. Select-Trac option would be similar to 4runner's.

Here's some more explanation on the 4wd system:

http://www.toyota-4runner.org/showthread.php?threadid=12

 

[Koz]

The difference between locking diff and 4wd is; 4wd means you are splitting the power between the front and rear. The percentage could vary or if you have a locking center diff this would split the power 50/50. This gets us to locking diff. A locking diff could be in the front/center/rear diff. What happens when you lock the diff is, it creates a solid axle and both wheel will/have to spin at the same speed regardless of traction. If you have a center locking diff it creates a solid drive shaft between the front and rear diffs. If you are on pavement and lock the front, rear or center diff and make a turn you will experience wheel hop. This is because both wheels HAVE to turn at the same speed and this is not possible because the inner and outer wheel need to turn at a different speed. On the 4Runner you only have a center locking diff because it uses traction control to divert power to the wheel with traction. Without the center locked the power is distributed 60/40 rear/front, and when the rear loses traction it automatically shifts up to 50% of the power to the front. If the front slips it automatically shifts up to 70% to the rear. Again, if you lock the center diff you split the power to the front and rear diff 50/50. There is a difference between a locking and limited-slip/posi diff. A limited-slip will shift the power to the wheel with traction and the wheels can still rotate at different speeds, so you will not experience wheel hop. I hope I didn't confuse.

Koz

 

[JB.]

As one who cringed upon realizing I had driven 10 or so highway miles with the diff locked and only discovered it while making a tight turn when getting gas, I've broken this down in my mind in detail. This is all theory for me and I welcome correction based on experience.

I assume in a rear locking differential during a turn on a traction surface the inner wheel will turn properly while the outer wheel hops from not being able to go fast enough. Applying this to the 4runner with diff. locked, I assume the same thing in the back except the open differential takes care of the outside, rear wheel. The front wheels are locked into the drive shaft speed required by the back and it's not correct for either wheel. I'm guessing the open diff. in the front takes care of the outer wheel again so it looks to me like all the binding force is put on the front, inside wheel and the binding force will be proportional to the tightness of the turn.

Probably more info than most care to know, but I'd be interested to get feedback from people experienced with lockers.

 

[Border411]

I assume in a rear locking differential during a turn on a traction surface the inner wheel will turn properly while the outer wheel hops from not being able to go fast enough.

From what I have experienced, the inside wheel will "hop" since the forces acting on the truck pushes the weight to the outside wheel, therefore making the inside wheel have less traction, and therefore hop. But I think everything else you said was right!

 

[JB.]

From what I have experienced, the inside wheel will "hop" since the forces acting on the truck pushes the weight to the outside wheel, therefore making the inside wheel have less traction, and therefore hop. But I think everything else you said was right!

I figured I'd miss something. I was thinking of a very slow speed turn and hadn't even considered the centrifugal forces of higher speed turns. My original assessment still seems right to me for a crawling speed turn on a high traction surface. I don't even want to try to figure out what happens when the tractions forces start shifting around.

 

[General Lee]

I'm confused

What kind of situations would warrant the use of locking the differential. Does it help in certain situations than regular 4WD?

Sorry for the ignorance

 

[Thai]

I'm confused

What kind of situations would warrant the use of locking the differential. Does it help in certain situations than regular 4WD?

Sorry for the ignorance

See my link above in my post. Basically, if you're off-roading or trying to get out of a snow/mud ditch, then lock the center differential. Otherwise, just leave it open.

Locking center diff = turning off VSC (but not ATRAC) + equal distribution of power to front and rear axles (50/50)

Open center differntial = VSC is on (good for on-road safety) + variable distribution of power based on traction (good for handling and turning corners).