HRunner

Hi everyone,

I am a newbie here... nice to meet you all.

I live in Canada and plan to buy a 2005 4Runner Limited very soon. After some research, I discovered that the US spec has more options, like 4x2 V6, 4x4 V6, 4x2 V8, 4x4 V8... etc.

In Canada, basically only have 2 options: V6 or V8. However, V6 limited has a Part-Time w/Multi-Mode One-Touch 4WD System, but for V8 is running Full-time 4WD.

I am wondering about the "Part-Time" one touch 4WD system. Some tech person told me that this PT 4WD is actually running 2WD. When you're stucked, then press the button to get 4WD... The most important, it is not recommanded to run 4WD at all time. Is this true?

How does this PT one touch system compared with the full-time 4WD, which one is better?

My intention is to have good 4WD system (I don't think I need 2WD for a 4Runner)... however, I am a little bit concern about the gas comsuming on V8. The best would be V6 and have full-time 4WD... too bad we don't have this in Canada.

I know there're many knowledgable person in this forum... please give me some suggestion....

Thanks a lot

CoedNaked

Part time systems have been in Toyota trucks and 4runners since their inception into the North American 4 wheel drive market. They are the reason these vehicles have become known as stock prodiguous 4 wheel drive vehicles. So consider this as well but...

In terms of the traditional part time 4 wheel drive system versus a full time 4 wheel drive system, well first I need to offer you a description of each to explain the why there isn't much benefit from a wheelin standpoint from one to the other, really.

Part time wheel drive system:
Your back wheels power the 4runner in 2 hi. When you put the truck into 4 hi, or 4 lo, your transfer case sends 50 percent of the engines power to the front wheels, and 50 percent to the rear wheels, as opposed to the 100 percent to the rear wheels in only 2 hi (2 wheel drive). When you are in 4hi/lo the transfer case will NOT allow power to be sent back and forth from the front wheels to the back wheels. Now each set of wheels (front, and back) has a differential between them. It is the differentials job to take this 50 percent of the power they receive, and send it to the wheels that require it on each individual axle. So, lets pretend you are turning left and you're in 4 hi (or lo, doesn't matter for this example). Picture the turn and what each wheel does. Your left front wheel needs 50 revolutions to turn. Your right front wheel needs 100 revolutions. You have your foot on the gas pedal, and your differnetial senses that you need more power to the outside wheel (through lesser resistance on that wheel) to complete this turn and it sends the appropriate amount of power to the outside wheel to make you turn. Now since you're in 4 hi, your back wheels differential also must do the same thing. But since the front left wheel, and the back left wheel do NOT take the same pathes, the back wheels in the same line need different RPM to turn as well. So again, the front left, 50 revolutions, the front right, 100 revolutions, lets say the back left 60 revolutions, the back right 90 revolutions. Now something you'll notice, is that due to the difference in revolutions from front to back, yet the power (or engine spin) can't be sent from the front to the back to make up for this, one of these wheels has to slip to make the turn. In this example, the front right (100 RPM) must slip to make up for the back right (90 RPM) lugging with less revolutions, and the back left (60 RPM) must slip due to the lesser rpms of the front left (50 RPM). If you are pavement, you can figure out that your turns won't allow this slip due to the friction between the tires and the dry road. And so you end up with something called axle bind, which is essentially the degenerative effects of having your differentials fight each other while in 4 wheel drive on pavement and doing turns. This is why you can not use 4 hi on pavement or in situations where the wheels can not slip to account for the differentials fighting each other during turns due to the fact that the transfer case won't allow sending rpm's back and forth between the front and back to account for differences in tire spin. But at the same time, having the system only allowing 50 percent to the front, and 50 to the back is actually beneficial offroad. But that's a whole other explanation I'll mention later on.

Now with full time 4 wheel drive, you have not 2, but 3 differentials. You have a front differnetial (between the 2 front wheels) and a back differential (between the 2 back wheels) and a center differential (betwen the front and rear differential). The Center differential allows the engines power to be sent back and forth between the front and rear differnetial to account for differences in turning RPM's. This effectively allows your vehicle to have all 4 wheels receiving power, on the pavement, while allowing you to turn without causing axle bind, because power can not only be sent from left to right through the front and rear differentials to their respective tires, but also back and forth to account for differences in wheel pathes during turns. On the 4runner full time 4wd system, there is a center differetial lock. When you lock the center differential, it no longer functions, and the 4runner's 4 wheel drive system now becomes the same as a part time system in 4 hi. It now can only send 50 to the front, and 50 to the back, like I just described. And you're probably wonder HOW this could be beneficial when the full time system sounds with the center diff functioning sounds like the perfect marriage of onroad and offroad driving?

Now you're thinking right now, well this part time crap, why have part time, full time sounds perfect! Well it is, but it isn't. Lets pretend you are out on a trail, in a part time system, in 2 hi, so only your back rear wheels are powered. Imagine you get into a rut, and your back right wheel goes into the air. Now, remember what the job of a differential is. It senses lesser resistance, and kicks up engine RPM to that wheel to effectively make a turn (or so it thinks). It senses lesser resistance and assumes that that is the outside wheel in a turn and again, kicks up the engine's power more so to that wheel as opposed to the inside wheel (the differential is just a dumb mechanical box basically - it can't reason). Well with that tire in the air with now what is very very little resistance (basically just air), your differential doesn't know better, and it kicks up the engines rpm's to that wheel - in fact ALL of the rpm goes to that wheel. And you're stuck. The differential doesn't realize that the wheel still on the ground, the one with some traction to push you out of this rut, is the one that needs the power. And this is why a part time system is beneficial. This is why it is beneficial to have only 50 percent to the front, and 50 percent to the rear, and no moving back and forth, of the engines power. In this case you would put it in 4 hi, you would have your 2 front wheels still on the ground, and they would pull you out of this rut because they both have traction still.

IN an full time 4 wheel drive system, with the center differential not locked, and thus it still has the capacity to send power back and forth, front to back, side to side, exactly the same thing would happen to you if you were stuck in a run as if you were in a part time system in 2 hi. Again, your back right wheel comes off the ground. Since your engine can send power anywhere in this system, the center diff and rear diff will kick up all the engines power to the spinning tire (basically sucking the front tires power and sending it to the back). And in effect, you are still stuck, just like as if you were in 2 hi in a part time system. This is when you lock the center diff, effectively turning it into a part time system in 4 hi, and again your front wheels pull you out of the rut becuase they have 50 percent of the engines power.

In terms of 4 wheel drive, the full time system isn't really superior in all honesty to a part time system. But I'm sure someone may want to chime in and mention some of the perhaps benefits of a full time system? In all honesty, I wouldn't feel shortchanged getting the part time system. It's very proven, reliable, less parts and less cost than a full time system, and I wouldn't personally feel short changed in getting the V6 if I were you either considering it's the same engine in the new Tacoma and the new Tacoma is the best performing truck by a significant margin, in it's class.

I could be wrong, but I also thought that full time systems might use slightly more gas than a part time system?

Anyways, I hope my descriptions satisfactorily explain the part time versus full time debate in a nutshell. Or at least some of my opinion of it anyways. If you have any questions just ask. BTW, where are you located in Canada?

lee

jeez... someone try to say yotatech isnt helpful NOW!

eric-the-red

To add to Coed's great description the only slight advantage I can see with a full time system is if you driving on roads that are partly ice and snow and part bare. With the full time system and trac control you can just leave it to do it's own thing, so to speak. With a part time system you would have to switch from 4wd to 2wd and back whenever you went from snow to bare road and back to snow.

Having said that my 93 has part time 4wd and it's not much bother to change from 2 to 4 and back, even easier with the newer models where you just push a button.

Personally I would go for the V6, unless you're going to be doing a lot of towing.

CoedNaked

Yeah I'd stick with the V6 too, unless of course like eric-the-red said, you're doing lots of towing on the heavier side. In fact I'd buy the V6 with the part time system and just swap out the stock tires for some solid all terrain tires like the BFG All Terrains, Bridgestone Dueller Revos, or Michelin LTX A/T (or any other highly recommended tires). If you're on a budget this will make a difference. Those crappy dunlop's or whatever they come with stock are city tires. I used to inspect Toyota's (4runners included), in fact I still do every few monthes or so when they need an extra guy, when they come off of the ships from Japan.

Swede

FWIW, I took a new '05 sport with the V-8 out for quick run on Tuesday and I have to admit that it not only has gobs of power but it sounds geat too.
The downhill descent feature is also pretty cool.