4 X 4 Nit-wit here... Please help me understand

[Mo2vation]

Background:
I've been driving a truck (in one form or another) since 1981. Always been a truck guy, except for my first car or two... When your a drummer, you drive a truck. Always had a shell (cap) on the bed.

For about a year in this span, I had a 4 X 4 Toyota Tacoma. It was a nice enough truck, but a bit underpowered for me and a little small, so when the Tundra came out in late 1999 I ditched it for a Tundra. Got another Tundra in 2002.

Well, I've officially left the truck ranks last week. I'm now driving a Land Cruiser (2000 M/Y) Its nice, its quiet, very low miles, very clean, turns tighter, has some of the fineries my Tundras didn't, etc, etc. I'm loving it so far. Its kinda weird not being able to just chuck stuff (dibris, yard trimmings, scrap lumber, etc.) into the back... as there is light tan carpet and leather seats to deal with. Throwing down a tarp is a little strange... kinda non-truck guy like - but OK. I drive a lot more than I haul stuff these days, so it was time.

The Question
I'm having a hard time understanding the full-time four wheel drive (apart from the fact it delivers an anemic 13.5 MPG) and specifically, the Center Differential Lock feature. I figgered there are lots of truck people here, and lots of 4X4 types who could help me out.

I get the whole "Second Start" thing, and the whole H-N-L shifter thing (had that on the Taco) but this Center Differential Lock thing I'm not so clear on. Lemmie take a shot, and tell me if I'm mental:

1) Its always in 4-wheel drive... hence the "full-time 4-wheel drive"

2) The Center Differential Lock button simply locks or unlocks the Center Differential. It says to keep it unlocked for most normal (read: on-road) driving. It says if you're slipping or need additional traction, push the button to lock it.

OK - so what does that mean? What does locking the Center Differential do? If everything is in full-time four wheel drive, what does locking the Center Differental do? Does it some how synch the front and rear wheels? Does it synch the right and left wheels of either the front and/or rear axel?

Pretty clueless here. If you can help me with the what it does, I can probably figure out the why and when stuff.

Thanks!

---
Ken

 

[teknitroxdiver]

(I'm 99% sure the following is correct....)

Locking the differential keeps all the power evenly divided between the affected wheels. For example, if you had one wheel off the ground with the differential unlocked, when you hit the gas the wheel off the ground would spin and the one on the ground would stay still. With the differential locked, the wheel on the ground would get half the power, which would hopefully move you along.

 

[Knight1989]

4wheel drive actually dosnt mean what most people think. It all depends on what differential locker you have. In your case, you have a selectable locking differential. Which means that when normal driving, all 4 of your wheels CAN be spinning. It basicly will delever power the the wheel that is recive the least traction. Good for on road driving, bad for off road. Which is why you have the Lock button, when you press that it locks your diifferential applying an even amount of power to all 4 wheels regardless of traction. Much better for off road.

 

[fdog]

A center differential is placed in the driveline between the front axle and the rear axle. It allows the two axles to spin at different rates.

An example of this would be a tight turn in reverse, where the front wheels have a greater arc than the rear wheels.

Locking the center differential forces the front and rear axles to turn at identical rates.

This would be handy if, for example, you were driving off of a frozen lake. As the front wheels hit the dirt, an unlocked center diff would allow the rear wheels to spin uselessly, while the front wheels did nothing. Stuck. A locked center diff would force front and rear to spin identically, and thus get you off the lake.

All the best, James

 

[Scubaroo]

If this is similar to other 4WDs (how the rest of the world refers to SUVs ), it is probably a bad thing to engage wihile driving on dry bitumen - as fdog said - "Locking the center differential forces the front and rear axles to turn at identical rates." Well if you're driving on dry blacktop, thanks to turning etc, your front and rear axles eventually end up travelling slightly further or short distances than the other - you can "wind up" tension in the drivetrain if you keep the centre diff locked - think of a short thick piece of rope being twisted - eventually you reach a point where you can't twist the rope anymore. You can do this to your drivetrain. When this occurs, it's almost as bad as the NSM adopting highways in Oregon. You'll just wish it hadn't happened.

So check the manual about whether it's safe to engage on dry hard roads, or whether you should keep it for off road use.

teknitroxdiver is thinking of a front or rear diff lock - this forces the two wheels on that diff to turn at the same rate, so if one wheel is off the ground, instead of it spinning like mad while the wheel with traction stays put, both wheels turn at the same time - so as long as one of your wheels has traction, you'll keep going forward. This is becoming standard on a number of different 4WDs in the rear diff, but is usually an after-market add-on in the front diff for the serious offroader. There is also the limited slip diff, which is also usually found in the rear diff - this works on a similar principle, but allows some slip (kind of like a clutch) to relief tension, so you can use it in more situations.

 

[O2BBubbleFree]

4wheel drive actually dosnt mean what most people think. It all depends on what differential locker you have. In your case, you have a selectable locking differential. Which means that when normal driving, all 4 of your wheels CAN be spinning. It basicly will delever power the the wheel that is recive the least traction. Good for on road driving, bad for off road. Which is why you have the Lock button, when you press that it locks your diifferential applying an even amount of power to all 4 wheels regardless of traction. Much better for off road.

I fell into this trap before, and had to spend a few minutes with an owner's manual before I figured it out.

When we US 4X4 nuts talk about locking differentials, we're talking about a 'locker,' 'limited slip,' or 'posi' pumpkin in the front or rear axel housing. The above quote is a good example (sorry, Knight1989). Your LR may or may not have such devices, but that's not what they refer to as a Center Differential Lock.

What Toyota is talking about WRT a Center Differential Lock is a limited-slip device in the transfer case (between the front and rear drivelines).

Your LC is all wheel drive, which supplies power to front and rear at all times through a limited-slip device. This way both drive shafts are always powered but allowed to slip so that one can turn a little faster than the other (as mentioned earlier, the only way you can have four-wheel drive on solid surfaces is to provide a slip mechanism).

When you engage the Center Diff Lock, the front and rear are locked together and turn at the same rate. This gives better traction for low-speed slippery surfaces, but can cause damage if used on dry, solid surfaces.

So, in effect, you could have three limited-slip differentials. One to split power between the front and rear drivelines (Center Differential), one to split power between the front tires, and one to split power between the rear tires.

 

[Mo2vation]

It makes sense - having the Center Differential Lock, and keeping it un-locked on the road. The driving off-the-frozen-lake sceneario made a lot of sense, as did the axel speed references. I really appreciate the info.

Living in SoCal (LA) its not real likely I'll be doing anything remotely resembling the Dakar Rally, but its good to know how to use what I got.

Thanks again!

---
Ken

 

[yukoneer]

Mo2vation - your question was answered, however if there's a technical aspect of 4-wheeling that you'd need to know, just ask me :-D I'm an avid 4-wheeler with my GMC Yukon.

http://www.yukoneer.com/

http://www.mudnuts.org/gallery/members_yukoneer