Might be the dumbest 4HI question ever...

When a vehicle turns, the wheels at the end of each axle turn at different rates. Open diffs allow for this.

The piece you are missing is that when a vehicle turns, the front and rear axles also turn at different rates.

Full time 4x4 requires a center differential to allow for the difference in axle speeds front to rear. Our trucks do not have center diffs. You see that more commonly on SUVs that have a locking center differential instead of a transfercase.

Another way to think of it, when you turn, all four wheels are turning at different rates.

Don't believe it? Put your truck in 4H and slowly idle forward with the wheel turned to one side. The truck will stop on its own as the drivetrain binds up. Reverse to release the binding and allow you to shift back to 2H.

This happened to me the first time I drove my truck as it's owner as the lot tech had left it in 4hi to pull it up the snowy show room ramp.

 

The problem is front to back and not side to side. Only a center torsen can accomplish this (“AWD”), which my FJ cruiser has, some 4runners, some sequoias, some Land Cruisers, etc.

Auto 4wd that other trucks have senses slip then engages/locks the center dif, which has pros and cons. I drive in 2hi most of the time in snow and flip to 4hi when I think I am about to get stuck or am stuck, makes me slow down and be tactical.

 

Just to reiterate some comments, what you want to avoid is SHARP TURNS. Broad turns the tires will slip enough to not hurt anything, frankly even sharp turns the truck will be fine. Driving down a highway that's dry in 4WD will be fine, driving through a parking lot in 4WD will be fine if you forget to switch out but is not ideal.

 

My wife left it in 4H on the elementary school pickup line. She made 3 full lock turns. When she got home she told me that she did not like that the truck "shook and jerked" on those turns. She promises me the pavement was snow packed....I then asked her to put it back in 2H before she attempts turns like that.

I've since taken her to a snowy parking lot to explore 4x4 and how it behaves when turning.

She also didn't know that you can unlock at any speed so that's why she had left it in 4hi.

 

This is my thoughts as well. The only thing that I feel may affect things is the gearing between front to rear. It used to be common to run an extremely off gear between to have the front always traveling further for better traction. Like a 4.10 front to 4.11 rear. To keep the rear of the truck from going out and around the front end of the vehicle. And added weight usually over the front wheels from the power plant.

 

Wait, didn't that Tacoma in your avatar have a J shift Tcase? It's the same stuff...

 

But you'll still get some chirping if turning - the tighter the turn the more chirping - indicative of stress and strain on the drivetrain (and accelerated wear on the tires).

 

Not sure what a J shift Tcase is, but it does have auto locking hubs with vacuum locking diff in the front. Im thinking it is what you are referring to. I can go to 4Hi on the fly. But… it is my son’s truck now. An amazing story behind the entire truck. It is in a post or two if you want to look it up. I can find the story and link it in here is desired and too much hassle to find it.

 

I appreciate you asking this. Being newer to 4x4, I still have lots of questions on how and when to use it. Currently I just engage it about one a week going straight up and down some hills where I live to to make sure everything remains lubricated. Haven’t found a need to use it.

 

What’s the difference between driving in 4lo crawling through rocks with tight turns and turning in 4h in a parking lot? If the former is ok then other than jerky steering going low speed in 4h should be fine. Doing a high speed turn in 4h on dry pavement would be the major no-no.

 

When crawling in rocks in 4Lo, you get wheel slip. Driving on dry pavement does not allow for much wheel slip.

 

I do miss the 4A setting on my F150, it was awesome.

 

Off-road trails aren’t paved. Dirt, sand, and loose rocks allow slippage rather than binding.

 

We had friends from Florida up in Winter Park, CO to ski last weekend. They rented a GMC Yukon. It was snowing most of the time. Since they aren't familiar with driving in snow, I was the designated driver.

I wasn't impressed with the 4 Auto on the Yukon. 4Hi felt much more sure-footed on the snow packed and icy roads. Overall, I think my Tundra handles those conditions better.

 

If you're going to be driving up to 50 mph on dry pavement in a straight line, make sure your tread depth is pretty much about the same on all 4 tires or you’ll be screwed once it binds up after traveling several miles and you can’t get out of it (or worse, break it).

I don’t believe there’s an official number for variance in tread depth but rule of thumb for most 4wd part time systems is 3/32 of an inch.

 

That's a lot. 6/32nds is a huge variance in tread depth. Anyone who rotates their tires will never see that much variance.

 

Sorry, typo. I meant 3/32”.

 

I think 4 auto uses clutches to engage the front driveline when it detects rear wheel slip. So the default is 2wd which is why it feels different.

 

I've wondered about the difference between GM's 4A and Toyota's Torsen center diff. Judging by this explanation of GM's 4A https://www.tahoeyukonforum.com/threads/4-wheel-auto-how-it-works.116141/

Gm's 4A is software-based (a Transfer Case control module and speed sensors on the front and rear driveshafts) and not as quick to react as the Torsen. This guy shows the Torsen operation is purely mechanical https://www.youtube.com/watch?v=pvF_P3vxzGM

Nerdy post, but thought I'd dig in and share. Torsen is very reliable, I don't recall seeing any threads among Yota forums about Torsen transfer cases failing. We have five in the fleet - three 2019 Sequoias and two V8 4runners. They use 75w90 gear oil, nothing fancy. The 4runner V8's don't even have 2WD, default is 4Hi.

 

I don't know what 'quick to react' means in this context, but my 3rd gen has the herkiest, jerkiest system in the real world. (highly technical term) My Denali or F150 lariats, I could be going around an icy curve in 4auto with traction control on, pin it, and the truck would magically just keep the line, or at least provide me confidence in its movements. My Tundra platinum on the other hand in 4wd will kick the back end out, make a bunch of noise, overcorrect, and I may or may not hit the ditch. Still having fun but there is no way no how whatever the Tundra system is is better than GM or Fords for the standard driver who simply wants control on an icy or snowy road.

 

I remember seeing this post by ViktorG a while back in the general supercharger thread so went and found it again.

https://www.tundras.com/threads/general-supercharger-thread.85513/page-87#post-2873454

 

Most of us will never have a reason to go faster than 40 or 50. If the roads are bad enough to use 4x4, they are bad enough to keep your speed down.

 

This is only the second part time 4wd I’ve owned. My first was an ‘86 Toyota standard cab, short american bed, carbureted 22r with 5spd manual. Those trucks were manual locking hubs of course. That truck would go anywhere you’d care to take it. What a blast to drive !! Had several 2wd Toyota pickups and a 2wd first gen first year Tundra. Sold my 2010 Limited 4Runner when I got the new Tundra. The Runners full time system really spoils you as far as road holding and traction with varying road conditions. Typically I’d never really need to go into 4HL, 4H would handle pretty much any type road conditions.

 

Just saw a 22R 4x4 for sale tonight. You’ll never guess the price.

 

One million dollars

 

Does anyone know why Toyota has never put a Full Time Torsen system in a Tundra? I wonder if they have it on the Hilux?

 

Let’s just say it’s 3.5x the amount I recently paid for a first gen 4x4 Sequoia.

 

Mine was a F150, I have not driven a Yukon. The 4A on the ford was seemless. I drove from Dallas to Colorado many times in that truck. I'd put it in 4A when I hit the Raton Pass and drive thru all kinds of weather snowstorms to Crested Butte, Breck, Steamboat you know it felt sure footed thruout. Carried chains, never had to use them.

Agree.

Yes and no. If you drive the highway in light snow, 4wd is nice and you could be over 50mph without being wreckless. They do in Colorado anyway!

 

My guess…… $15-$20 G’s