What exactly does switching to H4 do?

Just trying to figure out what exactly happens when H4 is engaged. Does it simply lock the transfer case? Does it also lock the front differential? Something else? Haven't found a clear answer.

And then what about L4? Is it the same as H4 only with the lower gear ratio engaged or is there something else also going on?

Thanks.

Dan

 

4H and 4lo is referring to the gear range in 4wd. In 4h the gearing is the same as when you normally drive in 2wd, except the transfer case engages the front diff so as to drive the front tires. Not to be confused with a locker. Not all 4 wheels are locked. Only 2 wheels are actually driving. Opposing corners front to rear, unless one drops out due traction.

4lo is 4wd in a lower gear. Crawling speed. Allows you to get through rough terrain easier and get unstock so the tires arent spinning so fast. Also not to be confused with a locker.

A locker will actually lock the driving tires together. So they both spin the same. You can have a locker in the rear, or both front and rear. The TRD offroad is the only one that comes factory with a rear locker. You can install aftermarket lockers if you choose.

 

Is there a way to change gear ratio in 4 lo so you can crawl better but keep the 4h gear ratio for winter driving/ easy roads?

 

Ok so all H4 does is engage the transfer case. Got it. However I don't understand what you mean by the above quote.

 

Both front and rear diffs are "open" this prevents tire spin when cornering (inside tire spins fewer times when going around a corner than the outside tire). Because of the open diff, there is only power going to one wheel per engaged axle at a time, so in 4H with no locker the truck has 2 wheels receiving power. With a limited slip in the rear (which I believe the Sport has) if the rear drive wheel starts to slip, power is transferred to the other wheel. But in the front, without a locker or LSD, the front tire getting power will just spin and the other will do nothing.

That's my understanding, at least. I'm sure someone will correct me if I'm wrong.

 

4lo is already geared really low. Its literally is a crawl gear.

 

This is pretty much it. Simply put, when stuck in snow or mud in 2H or 4H, the tire with traction stops spinning and sends power to the tire with slippage. Thats where a locker or LSD comes into play, or if you have the offroad, ATRAC. These send power to tires that actually have traction. Locker simply locks the axle so both tires spin.

 

It's also my understanding that, prior to 3rd Gen, the Tacoma was still using a very rudimentary 4wd system, which is good because it is stout and works well for people that have experience driving off-road or in less than ideal conditions. Prior to buying my Taco I was looking at Jeeps, and, for their serious off road vehicle (Wrangler) they still use simple technology (solid axles, manually switched transfer case, lockers/LSD, etc that transfer power based on physical forces), while their CUV/SUV offerings use a very complicated electronic traction management system where the computer takes samplings from all four wheels at a rate of about 10,000 readings per second, analyzes the data, then electronically manages power distribution of up to 100% of the available power being routed to one wheel. It's a pretty impressive system, but not one I'd trust out in the woods running through various depths of blackwater and muck.

 

Ok, so with an open diff, all the power automatically goes to the wheel with the least traction? If not then what determines which wheel gets power?

So the only way both wheels get power is if they're locked? So as long as the two powered wheels have traction I'm good. Otherwise I need to engage the rear locker (or ATRAC?)

Am I understanding this correctly?

 

I know but i want lower gear ratio to crawl better, and was curious how to make that happen
while keeping by daily driver capability. I am constantly wishing for a lower gear ratio while offroad but i drive through snow on an interstate daily in the winter so i need to keep the 4h capable of interstate travel. I am pretty much wanting the best of both worlds and though i would just ask. Sorry for the thread jack but this thread got me thinking about this.

 

The only way to do it with your chain driven case is by adding a second transfer case ("crawl box") into your driveline. Its expensive and a lot of work. Older Toyotas (think 80s models) have a gear driven transfer case that you can simply swap the gears in to gear it down to 4.7:1 ratio. I believe Tacomas have a 2.25:1 ratio stock.

 

Thats what i thought. best of both worlds==lots of money. I really just need a daily driver then i can do whatever i want. thanks for the reply.

 

You already have this. On dry pavement leave it in 2WD. On snow or slippery roads shift the transfer case into 4H. When crawling shift the transfer case into 4L. Unless of course you own a 2WD Prerunner and then you don't have 4WD capability at all.

 

https://www.tacomaworld.com/threads...rols-trac-auto-lsd-a-trac-rear-locker.212057/

https://www.tacomaworld.com/threads/traction-controls-2009-2015.310726/

 

I understand all of this but the 4l is not low enough for me offroad and what i like to drive and the control i want to feel. The above post states dual transfer case and that just solidified what i know but i was hoping it was not the answer because of how much they are and how involved the install is.

 

What about re-gearing the diffs? Obviously it would re-gear everything (2h, 4h & 4l). But would it be cheaper and easier?

 

Poor OP is so confused. Some of you guys are right, some are wrong. I'm going to try to explain this best I can short and sweet.

Our trucks have basic differentials. Watch this youtube video to learn what that means

https://www.youtube.com/watch?v=SOgoejxzF8c

To prevent the slipping wheel from getting all the power, our trucks have whats called TRAC / ATRAC. TRAC is used in 4H while ATRAC is used in 4L but both systems are similar. They use the vehicles brakes to limit the slipping tire, thereby sending the stuck tire some of the power. It works the same as a true LSD but more clever because brake pads can be cheaply replaced while differential LSDs are not cheap. These functions are automatically ON in ALL modes but can manually be turned Off by holding the VSC button while stopped. Doing this gives you a open differential which may be more practical in some situations but not many.

 

Whoa whoa whoa, hold up a second everybody

This is indeed wrong.

With open differentials it's impossible for only one wheel in an axle to propel the truck. By definition an axle is either giving power to both wheels approximately evenly or neither wheel.

Once again, said a bit differently, for open diffs: If all 4 wheels have traction, all 4 wheels are getting power.

For any given axle: If both wheels have traction, both wheels get power. If one (or both) wheels lose traction, neither wheel gets power, not even the one still touching the ground, even if it's not spinning.

Examples:

If you're crawling and your left front tire is off the ground but 3 other wheels are on the ground, the truck is being driven 100% by the two rear wheels.

If you're crawling and your right rear tire doesn't have traction, your truck is being powered 100% by your two front wheels.

If you're crawling and all 4 wheels have traction, you're being powered by all four wheels.

With open diffs in 4H or 4L you're either being powered by all 4, only 2, or none at all.

This does not necessarily apply to vehicles with lockers, although it depends which axle is locked.

 

This statement is not all together correct. In 2 wd one tire can spin while the other doesnt. Same as 4wd. Thats why there are lockers, ATRAC, and auto lsd. These systems compensate for loss of power to the tire with traction.

 

That is actually incorrect. Both sentences I've highlighted.

First off, the two wheels on an axle are ALWAYS receiving EQUAL power. This is the nature of a differential gear. What is happening when you observe "one wheel spinning" though, is that the spinning wheel is not able to deliver the power to the ground, it just spins easily, which means that the wheel that DOES have traction, is getting equal power delivered to it as well, and in this case, zero on the spinning wheel, means also zero on the wheel with traction. It doesn't actually mean what is commonly said "all the power is going to the wheel without traction", but actually "no significant power is going ANYWHERE".

The problem with your second sentence, is that it is just ridiculous. There is NOTHING in the drivelines that would send power to opposite wheels. If you're STUCK, you CAN have opposite wheels spinning, but you are JUST AS LIKELY to have two spinners on the same side of the vehicle.