Educate me..... Center Differential (Diff) Lock

[SnoViking]

OK folks... Please keep the flaming to a minimal.....

So I "upgraded" this past year and I'm running a GX460 which shares the 5th gen 4Runner platform. I have all-time 4 wheel drive with a center differential lock (same as the 4runner limited)..... I came from a 3rd gen 4Runner and I understand lockers for individual axles (ie front and/or rear) and I've read a limited amount on the Torsen differential and it's functionality....


So when would/should I use that little button with the "X" between the axles?

 

[Airmapper]

It locks the front and rear outputs together so power is split between them.

It's essentially 4HI on any other vehicle when you lock the center diff.

 

[AaronK]

Full time 4WD allows the front and rear drive shafts to spin at different speeds using a center differential. Locking the diff forces the shafts to turn at the same rate increasing your traction

Sent from my OnePlus One using Tapatalk.

 

[Buddha.]

So when would/should I use that little button with the "X" between the axles?


When off road/ on surfaces with poor traction.

 

[LocoCoyote]

Actually, you should be engaging it before you use the rear or front locks

 

[lugueto]

In order to allow all four wheels to have drive in hard surfaces, you need to have a center differential to account for the difference in rotational speed when turning. For example, In your old 4Runner, if you threw it in 4x4 while on a paved and made a tight turn or Uturn, the truck would skip and eventually the transfercase would've exploded, correct? This is what the center differential avoids.

Since you now have a center differencial, engine drive will follow the path of least resistance: when a particular wheel is free, the other three will stop while the free one will spin wildly, same as any of your axles when unlocked. Not good for slippery surfaces and proper off road driving, right? So now you need a locker to avoid this from happening.

So, for all intended purpose, engaging your center diff locker has the same effect as engaging 4Hi on your old 4Runner.

 

[Airmapper]

Maybe I've thought of a more organized way to put it...

Power as described here will flow to the point of least resistance assuming no devices to interfere.

AWD / Center diff unlocked = Power to front OR rear
4WD / Center diff locked = Power to front AND rear
4LO / Center diff locked = Power to front AND rear PLUS gear reduction

At that point when power goes to the axle, the same principle applies there with the axle diff:

Axle diff unlocked = Power to left OR right wheel
Axle diff locked = Power to left AND right wheel


3rd gen 4runners have about the same system with the "multi mode" t-case. In that case it is:

2WD = Power to rear ONLY
Press 4x4 button - AWD Center diff unlocked = Power to front OR rear
Shift lever to 4HI - Center diff locked = Power to front AND rear
Shift lever to 4LO - Center diff locked = Power to front AND rear PLUS gear reduction


In practical use, AWD is useful on mixed surfaces which vary between hard and slick. A half snow covered road is a good example, one curve may have snow on it, the next dry pavement. In this case the power can freely travel to any wheel and if any wheel binds or slips power will have somewhere to flow other than building pressure against a mechanical part. However given the power flows to any wheel it is delivered more evenly and provides better traction. Coupled with traction control systems which can overcome the "power to the point of least resistance" rule, this makes for superior control on surfaces that are variable and unpredictable.

4HI is useful on entirely slick surfaces where you need more traction than one powered wheel can provide, or need traction directly at the front axle. You are guaranteed one wheel in the front, and one wheel in the rear have power at all times. Given the slick surface, if any difference in pressure builds between front and rear, the tire can slip on the ground to release it.

4LO is for when you have the same conditions 4HI is useful for, but need additional torque to turn the wheels, or extra control at slower speeds. Assuming a 2:1 gear reduction ratio you will travel half as fast with twice the torque, or power to turn the wheel. This also halves stresses on the engine and transmission, making the vehicle feel unburdened where it might otherwise be having difficulty maintaining power or pulling itself. This is useful for climbing or descending grades, overcoming obstacles, or simply to make driving easier by going slower. It's also great for preserving your vehicle on trails by making it work less to accomplish the same amount of travel. (roll along at 1000rpm vs. 2000rpm)

For even more difficult conditions, then locking the axles comes into play, guaranteeing power to more than 1 wheel per axle at a time.

 

[Arktikos]

When off road/ on surfaces with poor traction.

That's it. Basically, when you're slipping in 4WD. We've had the scenario recently around here. Big snowfall and lots of narrow, steep roads with tight turns.. The center diff lock turns off the vehicle stability control, which allows the tires to spin in order to move on.

 

[JLee]

Maybe I've thought of a more organized way to put it...

Power as described here will flow to the point of least resistance assuming no devices to interfere.

AWD / Center diff unlocked = Power to front OR rear
4WD / Center diff locked = Power to front AND rear
4LO / Center diff locked = Power to front AND rear PLUS gear reduction

At that point when power goes to the axle, the same principle applies there with the axle diff:

Axle diff unlocked = Power to left OR right wheel
Axle diff locked = Power to left AND right wheel


3rd gen 4runners have about the same system with the "multi mode" t-case. In that case it is:

2WD = Power to rear ONLY
Press 4x4 button - AWD Center diff unlocked = Power to front OR rear
Shift lever to 4HI - Center diff locked = Power to front AND rear
Shift lever to 4LO - Center diff locked = Power to front AND rear PLUS gear reduction


In practical use, AWD is useful on mixed surfaces which vary between hard and slick. A half snow covered road is a good example, one curve may have snow on it, the next dry pavement. In this case the power can freely travel to any wheel and if any wheel binds or slips power will have somewhere to flow other than building pressure against a mechanical part. However given the power flows to any wheel it is delivered more evenly and provides better traction. Coupled with traction control systems which can overcome the "power to the point of least resistance" rule, this makes for superior control on surfaces that are variable and unpredictable.

4HI is useful on entirely slick surfaces where you need more traction than one powered wheel can provide, or need traction directly at the front axle. You are guaranteed one wheel in the front, and one wheel in the rear have power at all times. Given the slick surface, if any difference in pressure builds between front and rear, the tire can slip on the ground to release it.

4LO is for when you have the same conditions 4HI is useful for, but need additional torque to turn the wheels, or extra control at slower speeds. Assuming a 2:1 gear reduction ratio you will travel half as fast with twice the torque, or power to turn the wheel. This also halves stresses on the engine and transmission, making the vehicle feel unburdened where it might otherwise be having difficulty maintaining power or pulling itself. This is useful for climbing or descending grades, overcoming obstacles, or simply to make driving easier by going slower. It's also great for preserving your vehicle on trails by making it work less to accomplish the same amount of travel. (roll along at 1000rpm vs. 2000rpm)

For even more difficult conditions, then locking the axles comes into play, guaranteeing power to more than 1 wheel per axle at a time.

Great explanation for how open differentials work! In this case it's a bit more complicated because the GX has a Torsen center differential, so it's far more effective than a typical open differential:

The standard full-time four-wheel drive uses an electronically controlled transfer case and a TORSEN® torque-sensing limited slip center differential which can be electronically locked for inclement weather. It also offers a low range for off-road driving. The TORSEN differential distributes power 40:60 under most driving conditions and changes the ratio as needed based on steering input and wheel slip.

The ability to change to a 30:70 ratio during steering maneuvers helps enhance vehicle tracking through curves. If the rear wheels spin, the center differential can change the ratio to 50:50 to help control the slippage. The TORSEN differential also helps make the GX 460 less prone to slippage caused by sudden changes in road-surface conditions, such as driving through a puddle or over an ice patch.

I've had two wheels in the air with the center diff unlocked and ATRAC pulled me right through: https://www.youtube.com/watch?v=gEGcYfifL1k

 

[SnoViking]

Awesome!

Thanks everyone for the good answers. Those were all the ideas I was kinda thinking but wanted some reassurance. :bowdown:

 

[zidaro]

great explanations above!

Ill add-

30/70- split on Full time
50/50 split locked

 

[Drewskers]

Maybe I've thought of a more organized way to put it...

3rd gen 4runners have about the same system with the "multi mode" t-case. In that case it is:

2WD = Power to rear ONLY
Press 4x4 button - AWD Center diff unlocked = Power to front OR rear
Shift lever to 4HI - Center diff locked = Power to front AND rear
Shift lever to 4LO - Center diff locked = Power to front AND rear PLUS gear reduction

Same holds for 4th gen 4Runners with the V6 (the V8 models were full-time 4WD).

Additionally, 4th gen traction control uses the ABS system to brake a spinning wheel, which forces the axle differentials to provide power to the wheel with traction. Sort of a poor man's axle lockers! Works very well once you get used to all the racket the ABS system makes when it's happening, and don't back off the gas as a result.