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Discussion Starter #1
Howdy. I have looked around quite a bit and can't find an answer to this question. First off, I have a 2001 V6 4WD Tacoma with about 165k on it.

I know that driving the vehicle in four wheel drive on flat, dry surfaces will damage the truck. My question is, how anal should I realistically be about what constitutes a dry, flat surface? Currently, I err on the side of caution with it quite a bit. If there is just a light dusting of snow on the road, I don't use it. If there is a little bit of 'black ice' on the road I generally don't either if the ice does not seem to be rising above the texture of the pavement (ie in my head that currently means it's a flat surface and should be a no-no for 4wd). Am I being too careful with this? Pretty much my rule of thumb has been that if the tires will mostly still be interacting with the flat road surface I do not use it. I do understand that four wheel drive will only be of limited use on an icy road (mostly only helps with acceleration and staying in a straight line), but what I really am interested in hearing is if it will or will not cause the above-mentioned harm to the drive-train to drive on thin ice or snow in the cases I just mentioned.

Is the source of damage to the 4wd due to the flat surface itself, or from the surface not being slippery? I imagine understanding that distinction a little better will help determine what surfaces are appropriate.

If there is an existing thread or article that specifically addresses this (beyond the articles that state only in general terms 'if it is slippery use 4wd), then please point me to it and I will not take anyone else's time. Thanks.
 

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"Flat" doesn't really have anything to do with it.
It's the "dry" that matters the most.
If there's any snow/ ice under your tires then you're fine to use 4wd.
Since the front and rear tires have to turn at different speeds, the tires must be able to slip so you can turn without binding everything. If you're on a dry surface, all tires have full traction and no slip, you'll end up breaking a CV axle, diff gears, or worse, the transfercase.
 

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Discussion Starter #3
I did read that the main problem was with making turns. This is just an attempt to understand the engineering here...so the problem with a turn is that it changes the load/force/whatever you want to call it on each tire, and if one tire in particular is under more force than normal, such as the front driver's side on a right-hand turn, if it cannot slip it is going to put extra strain on that portion of the drive-train? And, in driving in a straight line, there is less chance of this. Why exactly are the front and rear differentials designed to turn at different speeds? I imagine it is due to the proper allocation of power is slippage at one or more wheels occurs, or am I completely missing the point?

So you're saying then that if the road is slippery at all, then there will not be a problem, as long as the wheel can slip? I guess that means if in doubt stop and accelerate to see if things spin.

Is damage from turning on a dry surface more of a built-up wear and tear, or is it a more immediate part failure? I imagine it could be both depending on the specifics of the turning event.

Thank you for the patience with my questions, I just want to get more specific understanding of the theory of how the thing works. :)
 

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Discussion Starter #4
Ok, I read up on differentials a bit more and I believe it makes sense now. Thank you for your reply Scuba.
 

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The key is that your front and rear drivelines are locked together at the transfer. So turning is the big issue, when the front and rear axles rotate at slightly different rates. This causes driveline bind.

If the roads are only a little slick, feel free to use 4wd, but try to shift to 2wd when you don't need 4wd. That will reduce potential binding.
 

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If you are reading the owners manual, it contradicts itself by also stating to drive the vehicle in 4wd 10 miles a month to keep from having seal damage. I would say you should be fine dring on the icy roads as long as you are not spinning tires whenever you shift into 4wd. if you have to turn while in 4wd do it without to much acceleration to prevent binding. Some of the hell we put these trucks through playing on the rocks is worse than what the pavement will do.
 
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