School Me on 4hi/lo/locked/unlocked

[Bruce Colbert]

Long time Toyota owner, first time Sequoia owner as of this weekend. Don't have any experience driving AWD/4WD. Can you school me on what situations I might use 4hi/4lo with and without lock?

For example, did a lot of driving around this weekend with slippery roads in 4hi/unlocked. When would I want to lock it? When going through a foot of snow? Or save the lock only when stuck?

I'm not really an off-roader, so are there any situations where I would really want to go 4lo?

Thanks...

 

[toyotafan]

What year is your Sequoia again? I seem to remember you mentioned a couple of different years but I don't remember what you have now and I'm doing something else (maybe I'm just too lazy) so I can't go look. ??

 

[Bruce Colbert]

What year is your Sequoia again? I seem to remember you mentioned a couple of different years but I don't remember what you have now and I'm doing something else (maybe I'm just too lazy) so I can't go look. ??

2005

 

[toyotafan]

From what I understand, the Sequoia (and some 4Runners) have a multi-mode full-time 4WD system.

This means that the system operates in full-time 4WD but it will function and act like a 2WD vehicle most of the time when there is no additional traction needed. This will give you better MPG and it will reduce the wear on all of the 4WD components.

The reason that it can do this (and also be driven on dry pavements in "4WD mode") is that it has a center differential that can be controlled by the system's computer to transfer power from front to rear as necessary to improve traction control and also to prevent the drivetrain from binding on dry pavement.

It's that extra feature (which is a good thing that you have it) that is lacking on part-time 4WD systems.

Now, I'm going off memory from this and I found an old PDF that doesn't cover the specific years, but from what I understand of the Sequoia, I think there's a good chance this is covered back to 2005.

 

[toyotafan]

... and I think the locked/unlocked is just letting the system balance power to make it act more like a 2WD system and if you lock it, then it's forcing it into 4WD without the balance ... something like that. Not exactly sure if it's a 50/50 or what though.

 

[Toyota Girl]

so i'm guessing that you would want to lock it if you're into anything really slippery where you might lose traction at any given time. like lock it down when you are in snow, heavy rain, ice, dirt roads, gravel roads, etc. but maybe just keep it unlocked if you're in light rain or like the old bumpy paved roads or just normal driving? that seems to make sense to me?

 

[Spec E30 Racer]

I had a 2005 4wd and if I remember correctly, here's what to use, and when.

1. 2wd is strictly rear wheel drive. Some of the 4wd parts are spinning (halfshafts, etc) but are "freewheeling" - that is no engine torque is sent to the front. Use this anytime. Fuel mileage is best in this mode, if only by a little bit.
2. 4wd high (center diff unlocked) can be used anytime. Some torque (I don't know what percentage) is sent to the front drive components. I used this in mud and snow and it worked well for what I needed. Dry pavement is fine to but fuel mileage will suffer slightly. Since the center diff is unlocked, you can turn (front and rear drivelines turn different speeds in turns) or go straight.
3. 4wd low can be used just like 4wd high but the gearing is significantly reduced. For example (I'm making up the numbers but you'll get the concept), if 20 mph in 4wd high turns the engine at 2000 rpm in first gear, the engine will be turning at 4000 rpm in first gear at 20 mph in 4wd low. I used it a couple of times to pull my sailboat and trailer out of the lake and up a steep dirt bank. Low speeds only and it'll pull like a tractor because of the lower gearing. I also locked the center diff because I was on loose dirt. See "Locked" below.
4. 4wd locked is used ONLY in low-grip conditions like mud, loose dirt, snow, and ice. Do NOT use it 0n wet or dry pavement. This basically locks the front and rear drive components into one complete and locked system. As long as you're driving straight, you're good, But if you turn at all and there's no slipping of the tires (like in mud or snow) the driveline will bind and the truck will bounce around. This is VERY bad on the driveline parts. From my understanding, if you're using 4wd unlocked, some slippage in the center diff can allow the engine torque to go to the spinning tire(s), which reduces torque to the gripping tire(s). 4wd locked sends the same amount of torque to each tire regardless of which tire is spinning and which tire has grip. Use the diff lock only in very slippery conditions when you want maximum torque at all four tires.

 

[Spec E30 Racer]

Toyota Girl is basically correct except you don't want to lock the center diff in rain - even heavy rain. 4wd without locking the center diff will probably work just fine for 99% of the time that you need 4wd.

 

[Bruce Colbert]

Thanks much @Spec E30 Racer . Worries me a little that the lady who I bought it from said she used to lock the differential a lot in snow...but on the other hand I'm not sure she actually was getting it locked, she said she would push the 4hi/lo then immediate push the differential lock, it may not have taken for her. Seems like she would have known something was wrong with that kind of feedback from the Sequoia ("bouncing around")

At any rate, hat tip for the very thorough, informed answer.