Purpose of rear locker in 4wd only?

[emerica243]

Take it easy on me. First truck, first time learning these systems. What is the benefit \ purpose of locking the rear diff. where it only works when the vehicle is in a 4wd mode, let alone ONLY 4lo? My understanding is locking the rear diff forces the two rear wheels to rotate at the same speed. But if youre in 4lo, and 4hi for that matter, all the wheels are rotating at the same speed already, no?

Its my understanding that in 2hi, one of the rear wheels is driving the vehicle, normal 2wd vehicle behavior. In 4hi, all 4 wheels are rotating at the same speed driving the vehicle, and 4lo, all the same, but lower gear ratio\more torque.

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[Irvin]

There arequite a few fantastic short videos on YouTube that will explain all your 4WD questions. Including when to use your 4WD so you don't damage your vehicle.

 

[emerica243]

There arequite a few fantastic short videos on YouTube that will explain all your 4WD questions. Including when to use your 4WD so you don't damage your vehicle.

Reading the manual and the slew of posts I understand the limits and requirements of when to use and engage said modes. I really only had one or two specific questions here as I try to understand more specifically

 

[Sagebrush]

But if youre in 4lo, and 4hi for that matter, all the wheels are rotating at the same speed already, no?

Nope. Not if one is slipping.

I use my rear locker a few times a year in deep snow and it makes a huge difference.

 

[ORHV]

In 2WD one wheel drives the rear axle.
In 4WD one wheel is ALSO driving the front axle.
In 4WD LOW with the rear axle locked, BOTH rear wheels are driving.
So (in a Tacoma!) it is at best a 3WD vehicle. Wish we could engage the locker in 4high and even 2WD like other manufacturers, but that’s another story!

 

[Miqie]

In 2WD one wheel drives the rear axle.
In 4WD one wheel is ALSO driving the front axle.
In 4WD LOW with the rear axle locked, BOTH rear wheels are driving.
So (in a Tacoma!) it is at best a 3WD vehicle. Wish we could engage the locker in 4high and even 2WD like other manufacturers, but that’s another story!

Is it always the driver side or pass side? Also, what's going on when you turn 'traction control' off?

 

[JakeJoeBob]

You are on the right track. Think of it like this, the power always follows the path of least resistance. Toyota has a lot of traction control systems (A-TRAC but in the background) that try to mitigate this which is one of the reasons these trucks are so great offroad even in the lower trims. MTS/crawl control takes all that a step further. With Traction control off, In 2wd all the power goes to one wheel in a low traction environment like sand or deep snow. In 4wd, same thing but now we are including the front wheel. All of the traction is going to one of the front wheels with no traction and one of the rear wheels with no traction. A rear Locker locks the rear differential together give the same amount of power to the rear wheels no matter the amount of traction. Front lockers do the same thing but we havent gotten one of those in a stock Taco yet. 4 Lo just changes the gearing ratio like you mentioned, more torque and better throttle control. I do wish Toyota let us Lock the rear anytime, would be fun when playing in the sand lol

 

[Delirious]

In 2WD one wheel drives the rear axle.
In 4WD one wheel is ALSO driving the front axle.
In 4WD LOW with the rear axle locked, BOTH rear wheels are driving.
So (in a Tacoma!) it is at best a 3WD vehicle. Wish we could engage the locker in 4high and even 2WD like other manufacturers, but that’s another story!

So let me get this right. I paid $57,000 for a four-wheel-drive truck and I only got a 3 wheel-drive truck? I want a refund of $14,250 for the fourth wheel I paid for

 

[ORHV]

So let me get this right. I paid $57,000 for a four-wheel-drive truck and I only got a 3 wheel-drive truck? I want a refund of $14,250 for the fourth wheel I paid for

Me too!

 

[ORHV]

Is it always the driver side or pass side? Also, what's going on when you turn 'traction control' off?

I dunno which side is ‘driven.’
Turning off ‘traction control’ would be best suited when you are stuck. Or almost stuck.

 

[LincolnSixAlpha]

Sounds like you need to research some basic understanding of differentials. I'd recommend that, and what that means in the way wheel's are driven on an axle. There are many types of diffs's, tacoma is is basically an open diff which is emulated by brakes to make it a limited slip diff. Locking does exactly that, locks the wheels together. That's great for Offroad, but you won't really need a locking diff at high speeds. Simply throwing the selector in 4Hi will split the engine's torque load normally destined for the rear to the front, making it easier to get started in snowy conditions, Offroad, etc. Important for you to understand that this is what's known as a part time 4WD system, and is not a full time system. Beyond that it's also important for you to understand that you'll never want to engage your 4WD system on dry pavement. Wheel slippage is important for part time 4WD systems. Youtube is your friend with respect to this. Don't feel like you have an inferior system, PT4WD systems are awesome, just need to know how/when to make use of them. They are also more reliable than full time systems in my humble opinion, but that's left for further discussions.

Also the wheel with the least amount of traction will slip, or rotate and take the engine's power. In yesteryear this was the norm, limited slip diffs (mechanical) were usually an upgraded to these vehicles. Limited slip, as mentioned above, is now controlled via the brakes "automatically" which makes the vehicle feel like it's got a limited slip diff. Again YouTube for your visual understanding.

 

[Delirious]

Sounds like you need to research some basic understanding of differentials. I'd recommend that, and what that means in the way wheel's are driven on an axle. There are many types of diffs's, tacoma is is basically an open diff which is emulated by brakes to make it a limited slip diff. Locking does exactly that, locks the wheels together. That's great for Offroad, but you won't really need a locking diff at high speeds. Simply throwing the selector in 4Hi will split the engine's torque load normally destined for the rear to the front, making it easier to get started in snowy conditions, Offroad, etc. Important for you to understand that this is what's known as a part time 4WD system, and is not a full time system. Beyond that it's also important for you to understand that you'll never want to engage your 4WD system on dry pavement. Wheel slippage is important for part time 4WD systems. Youtube is your friend with respect to this. Don't feel like you have an inferior system, PT4WD systems are awesome, just need to know how/when to make use of them. They are also more reliable than full time systems in my humble opinion, but that's left for further discussions.

Also the wheel with the least amount of traction will slip, or rotate and take the engine's power. In yesteryear this was the norm, limited slip diffs (mechanical) were usually an upgraded to these vehicles. Limited slip, as mentioned above, is now controlled via the brakes "automatically" which makes the vehicle feel like it's got a limited slip diff. Again YouTube for your visual understanding.

Thank you for the post. And yes, I always tell everyone that YouTube is your best friend for learning something.

 

[HardShellTaco]

This is a very good video on differentials - Around The Corner - How Differential Steering Works (1937).

When you engage your rear locker, you take differential steering out of the equation. Your wheels both get the same power and both turn at the same speed. This would bind up your drivetrain and make the tires skid on dry pavement (if you don't break a U-joint first), but if you're in something really slippery like deep snow or slick mud, it can be a big help to give you the traction you need.

People who build cars for burnout competitions actually weld the diff so it's permanently locked because they WANT the wheels to spin.

As for, "why four wheel drive only," it would be possible to lock the diff in two wheel drive, but I guess Toyota figures if you're in a situation where you need a locked diff, you're already in a situation where you'd need 4WD.

A funny thing about the video - it foreshadows driveline angles, which are a hugely important issue when you're talking lift kits and modified suspensions. If that piques your interest, search on, "four-link suspension explained." Warning, though - you'll go waaaay down the rabbit hole if you do.

 

[TrustButVerify]

I think it's a risk management feature. Most of the traction control systems that are on especially the newer Toyotas are so incredibly well designed they all but make the utility of a locker pointless.

Of course there's always some Bubba out there who will be like "well this one time, and this one situation, I was in this one place, once and the rear locker got me out."

OK.

You can do a lot of damage to a vehicle with a rear locker engaged in situations it shouldn't be engaged. The times when it *shouldn't* be used are about 1 million items long and the times it should be used are about six bullet points.

So I think the whole idea is the user of the vehicle must deliberately go out of their way to engage all of these different systems, and then disable all of the traction and safety systems, and then finally after all of those conditions are met, you can engage the rear locker.

Now personally I feel like you should be able to destroy your vehicle if you want. I would like to be have the option to use it in 2WD., 4 high, whatever. But I do understand why that's not a great idea from a risk management perspective

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