99 4WD Drive Train Questions/Information

T

Tswizzle

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I have owned a 99 Limited for about 4 years now. I have always wondered about the center differential and the ability to steer while the center is locked.

Can you 4Runner tranny experts chime in?!

OK so on this subject there are so many ifs. Here is a scenario that I need to figure out.

I am on difficult trail in Colorado and I am descending or ascending steep switchbacks, its a dry day and the trail is dry, its a rocky dirt surface, I am in 4low (because of steep conditions, using the braking a power) with the center locked, on 99 to get into 4low you have to have the center locked.

So when I turn at the switchback I am nervous that I might be damaging my differentials because the center is locked and I am making a sharp turn on what I consider dry surface. Should I rely on the rocks to give way to my differential...? I know doing this on dry pavement is not good and your front end would rock and damage gears over time. In this scenario I do not want to use the standard 4wd with all differentials opened because there is not a lot of power there, I prefer 4low when on steep trails and when I need more precise control.

I almost wish on the 99's you could be in 4low with the center opened. In fact I believe on the 4th generation models this is an option.

Anyway any 4WD information on the 99's would be awesome, I love my truck!
 
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the 99 Limited models have an electronic rear locking differential, the sport and base model did not have this.

So the viscous coupling? Would this protect the differential on dry pavement? I know my truck makes noises and wobbles with center locked on dry pavement.

Lets keep this topic going. This forum needs a thread on 3rd generation 4WD info and on how to use it!
 
Also the purpose of the center differential is to make the front and back turn at the same rate right? So I wonder why a viscous would be used. Thanks!
 
long story short it's not good for it but won't kill it either, it sounds as if that may be bad, or these tc's don't have a vc in them which i find hard to believe,
as a center locking diff is essentially the same thing as being in 4wd .

the binding that your experianceing is becuase your locked from front to rear and when you try and take a turn the front and rear are trying to follow the same path at the same speed, which will cause all sorts of problems.
http://www.4x4abc.com/4WD101/locking.html
http://auto.howstuffworks.com/differential.htm

i can;t comment on the toyta center locking diff but i'm pretty sure it has a vc and is not truely locked ..

but i'll concede to other on this and many other points ;-)
 
The point the OP brings up is the same point me and some others were trying to make in the 5th gen thread.

On the 99LTD, when in 4Lo you are automatically center diff locked. When off road going down a steep incline you need to be in 4Lo no doubt to use the lower gearing. But you are center diff locked with no way to unlock like the 4th gens can as well as the 2001-2002 4Runners can. So a sharp switchback turn comes up and you feel the binding because the surface is not slippery enough to let a wheel spin. There is no real need to be locked but you have no choice. What will happen is something will eventually give. Since you are off road, a tire will most likely be forced to slip...but if it cant something may break. I dont off-road enough in general to comment any further especially in those situations, but I have been in them in my 3rd gen and stay in Lo for the gearing and hope the tire slips. But my sR5 does not have a choice to stay in 4WD high unlocked like your limited does. In that case the decision is up to you of course but I would still go into lo for the gearing as I havent heard of anyone breaking stuff other than in theory.
 
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theizzardking said:
is there a blue/grey wire type mod for this then? sounds like there should be.
Click to expand...


havent heard on one for the 3rd gen. BUT I do have an inkling that a mod may be able to be implemented on the 5th gen to unlock the center diff while in 4Lo.
 
I have a '99 SR5. I just replaced my transfer case and do not have the LCD option. In fact, looking at my TC, I saw no place for a center diff. To my knowledge, mine is chain driven. I don't really see the need for a center diff in this case, being that both front and rear diffs are open. Correct me if I'm wrong.
 
Tswizzle said:
That mod is for newer 4runners. Looks like the same situation however...
Click to expand...

yeah but think about it, pull up the wiring diagram for our '99's and tray and follow along but only with your ride. it should be applicable to the earlier ones as well, that meaning even though the location and color of wires has changed
it still operates the same, so therefore you should be able to make this work somehow, find a wiring diagram for yours and see if it'll fit,

my '99 limited has the rear diff lock not the center, and i really don;t get the point of center diff lock anyways isn't that just 4wd?
 
Izzard:

I believe the benefit of locking the center is lets say your rear is in the mud, your front tires when turn at the same rate as your rear and pull you out. I guess the rear wheels will keep on spinning but at the same rate as the front, so as they front carries you out your rear wheels will keep on trying to push you out... thats my way of trying to rationalize that...

If you have a 99 Limited 4wd, then you are locking the centers with some functions, you just might not realize it.

OK so on the 4wd shifter there is the button on side of shifter, thats 4wd with all differentials open, now if you take the shifter and pull it down into 4high, now your center is locked, notice the orange dot in the middle of the 4 green tires on your dash. (With just the push button 4wd engaged you only have 4 green tires lit up on your dash) Now put the vehicle in neutral then shift the lever into 4low, the dash lights stay the same (4 green with the center orange lit up). To go even further you can now engage your electronic locking rear differential under 5mph, this is a button on the dash left of the steering wheel.

Does that describe your 99 Limited? Now if you have a 99 Limited that can be in 4low without the center locked then I want your truck! :-)
 
Tswizzle said:
Izzard:

I believe the benefit of locking the center is lets say your rear is in the mud, your front tires when turn at the same rate as your rear and pull you out. I guess the rear wheels will keep on spinning but at the same rate as the front, so as they front carries you out your rear wheels will keep on trying to push you out... thats my way of trying to rationalize that...

If you have a 99 Limited 4wd, then you are locking the centers with some functions, you just might not realize it.

OK so on the 4wd shifter there is the button on side of shifter, thats 4wd with all differentials open, now if you take the shifter and pull it down into 4high, now your center is locked, notice the orange dot in the middle of the 4 green tires on your dash. (With just the push button 4wd engaged you only have 4 green tires lit up on your dash) Now put the vehicle in neutral then shift the lever into 4low, the dash lights stay the same (4 green with the center orange lit up). To go even further you can now engage your electronic locking rear differential under 5mph, this is a button on the dash left of the steering wheel.

Does that describe your 99 Limited? Now if you have a 99 Limited that can be in 4low without the center locked then I want your truck! :-)
Click to expand...

yeah that's it yours is a standard limited with no diff lock, we're all confused becuase on some models there's an actual center diff lock button on the dash, what your describing is just normal 4wd in the yota.

the differance between the button on the side and the shift stick is one is AWD and one is 4WD, teh center lock your speaking of is just true 4x4 the other (button one on a '99) is AWD and uses the viscous coupling i was talking about earlier,
i think what you want to do on coming down the steep slopes is just use the AWD function and down shift in to first with the gear selector
that should be the same as what your trying to do as far as tq braking goes and won't screw with your joints
 
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Guys, you are getting confused. The VSC off mod for the 4th gens has nothing to do with the OP's issue of unlocking the center diff in 4Lo.

Next, the 99 Ltd's all have a center diff. And in 99 the rear diff e-locker was optional even on the Ltd. A $340 option iirc.
 
The OP asked a good question, and you answered it yourself, a loose dirt and rock trail offers sufficient slippage for the most part. Now if you are going around a tight corner on one solid rock that all 4 tires are in contact with it may bind. But the chances of that scenario are slim and the rock is probably not perfectly flat, meaning your suspension is flexing a bit freeing up pressure somewhere, its not like flat pavement. Minus a rear diff lock you have open front and rear diffs, locking the center does not change that, so around those tight corners you really only need one wheel to be able to slip, it doesn't even matter which one it is, so 3 wheels on rock and 1 on dirt and your fine.

Now as for viscous coupling last I checked this is not a Subaru forum, there is no viscous coupling going on inside these transfer cases. With or w/o the center diff a Toyota transfer case is a purely mechanical unit, and yes they are chain driven. The center diff set up in the 99/00LTD and all 01-02 4WD uses a system of planetary gears and doesn't really look like a differential at all, its just a name implying it allows that slippage front to rear.

A center diff is included in a 4wd for one reason, it allows slippage between the front and rear axles making it safe to use 4wd under any circumstances. When you lock up the center it takes away that ability to slip. With the center diff locked the characteristics of the front and rear axles do not change, they are still both open unless rear diff lock equipped. The reason to lock the center diff is to defeat VSC for real off road situations. VSC is vehicle skid control and it can de throttle your vehicle under certain situations, like if a tire is slipping. Off road sometimes you need to spin the tires to get traction, with VSC on you would not be able to do that.
 
pat161 said:
The OP asked a good question, and you answered it yourself, a loose dirt and rock trail offers sufficient slippage for the most part. Now if you are going around a tight corner on one solid rock that all 4 tires are in contact with it may bind. But the chances of that scenario are slim and the rock is probably not perfectly flat, meaning your suspension is flexing a bit freeing up pressure somewhere, its not like flat pavement. Minus a rear diff lock you have open front and rear diffs, locking the center does not change that, so around those tight corners you really only need one wheel to be able to slip, it doesn't even matter which one it is, so 3 wheels on rock and 1 on dirt and your fine.
Click to expand...

Just to add to this a couple of points: First of all, if you're off roading, chances are really good that you're going to be lifting a tire here and there off the ground - that will also allow slippage which is why you generally don't need to worry about driveline binding when you are off road.

Second, just so you understand, the center differential on full time 4wd or multimode 4wd vehicles is there to allow you to use the 4wd on dry, hard surfaced roads. Off road or on slippery surfaces it is usually best to lock out the center diff, otherwise one slipping tire could leave you stranded.

Don't worry too much about driveline binding when the center diff is locked. Think of it this way: When you lock the center diff and the power is split 50-50 between the front and rear, your vehicle is acting like a conventional 4wd vehicle - the same kind of 4wd vehicles people have been driving since before WWII.

A final point is that your driveline is not as fragile as some people think. IOW, it's not like if your driveline is exposed to a little stress it's going to spontaneously explode. It takes a while to build up the stress neccessary to cause damage to the axles, t-case, transmission or tires.

Around here, sometimes (like a few days after a major snowstorm when the main streets have been cleared but there are still patches of ice and snow) I'll drive around with the 4wd engaged, even on pavement. My reasoning is, I'll hit enough snowy/icy patches for the wheels to slip and allow the driveline to relieve any built up stress. I've been doing that for darn near 30 years on 7 or 8 4wd vehicles (all with conventional 4wd) and have never had a problem.
 
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