differential Lock

[runnerfreak]

I have a question,
When I'm driving with 4wheel drive (4H), how fast can I go? I know that I have to be driving at speeds below 62 mph to shift into 4 wheel drive.

Also, when can I use the differential lock? Is it for power distribution to all wheels? or is it power to each wheel (independently)?

 

[Thai]

When in 4-HI, you can go as fast as you want...just like when you're in 2wd mode.

The center diff lock does two things:
1. It locks the power distribution front and rear equally.
2. It turns OFF vehicle stability control (VSC), but NOT ATRAC (4-wheel traction control).

Center diff controls power flow front and rear axles. ATRAC controls side to side (left & right) power flow.

See this thread for more info: http://www.toyota-4runner.org/showthread.php?threadid=12

How ATRAC works? See: http://www.toyota-4runner.org/showthread.php?s=&threadid=5036

Hope this helps.

 

[keylay31]

As Thai has already covered, you can go as fast as you want in 4Hi. In fact, the V8 is all-time 4Hi. I wanted to add two things. I believe there is a limit to speed of changing between 4Hi and 2Hi which is around 65mph. Secondly, As someone noted on this forum about a year ago, why would you ever want to go above 65mph in 4WD? I can't think of an instance.

 

[Baba Booey]

You should only lock the center differential when driving off-road or in snow, for example. Basically, locking the center differential prohibits the front and rear wheels from being able to rotate at different speeds. Without this ability to "differentiate" the rotation between the front and rear axle, your vehicle's drivetrain will bind, chatter, and generally not be happy. Damage could occur.

In other words, the 4Runner with the center diff locked is really the same as an old-school, part-time 4WD system that can not be driven on dry roads. However, unlocking the center diff is what enables the 4Runner to be driven in 4WD on dry roads because the wheels on the front and rear axles are free to rotate at different distances.

Whenever a vehicle is not being driven in a perfectly straight line, the front and rear wheels track on a different path, as do the left and right wheels on the same axle. This is what differentials are for. They allow wheels to spin at different distances and speeds without binding.

Check out this article that Thai (our moderator) has linked to in a "Sticky" posted in the Off-Road forum:



How Differentials Work

 

[Thai]

Secondly, As someone noted on this forum about a year ago, why would you ever want to go above 65mph in 4WD? I can't think of an instance.

Why not? I think that 4wd at highway speed provide additional traction advantage over 2wd. Sure, VSC is the main thing, but having power delivered to both axles all the time is a good thing.