Toyota 4WD systems explained

stomlinson

When engaging 4L in L/gear (stopped) do you leave the tran in L or are able to shift into D and let the tran upshift as speed increases? It seems if I shift up from (tran) L the lock/diff light goes out.

pschreck

On a 2001 MY you must leave the tranny in L in order for the center diff to remain locked. I believe that changed on subsequent MYs.

clseib

I found the following description of 2004 Tacoma 4WD system on a car review website.

"...the base 4WD system requires that the vehicle be backed up a few feet to fully disengage 4WD; that's not necessary with the "selector switch" option available on V6 Xtracab and Double Cab models."

Is this true? Do you really need to back up to disengage 4WD without the 4-HI selector switch?

albiv

That's how I used to do it on my Tacoma 4x4 and pre Tacoma 4x4 with manual locking hubs.

clseib

So if I get the Hi-4 Selector switch option can I disengage 4WD "on the fly"? The Tacoma I test drove didn't have this option otherwise I would have tried myself.

stomlinson

Thanks for the info just got the unit back in Feb-04 and really enjoying it, found the manual a little vague, is the center diff chain driven when when in L gear 4L? I only use it pulling the boat up the (tidal location) ramp (5400lbs) so when I shift the tran into Drive and the diff unlocks, what is the status of the running gear in tech terms cause it just jumps through the gears, do I need to do a stop, neutral, to shift the system into 4H? (have been doing that)
What about continuing to use 5w/30 oil I see no recommends to run a heavier oil? I'm using 89 octane, the wife romps the thing like it's a 5.0L, what about engine flush treatment at oil changes, and using Duralube?
Thanx

spearsbm

We are buying an SR5 this week and are planning on the 2x4, mainly for financial reasons. But now I'm second guessing our decision. Is it a mistake not to get the 4x4?

We will not be doing ANY towing or off-roading. We're in Kentucky, so we maybe see 2-3 snows a season (and if i don't absolutely have to get out, i don't).

Do you think we'll be ok with just the 2x4?

gkatz1

You'll be fine, sounds like you don't need 4WD down there. Up in MA we have a fair amount of snow and lots of Ice on the roads in the Winter so 4WD makes sense.

wwest

The Sequoia id RWD and were I you I would carry around a set of snowchains during the winter just in case.

I survived many years in north central MT with a RWD ford sedan and snowchains as needed.

bp3959

Even without winter conditions 4wd isn't a bad option. It'll help out when the roads are wet, improves handling in high winds, and even helps in clear calm conditions. Alot of people complain the traction control on the Sequoia kicks in when taking off and throttles the engine cause the tires lose traction, one way to avoid this is use 4wd and you won't lose traction taking off or accelerating from a turn.

spearsbm

Well, even after signing a contract with VIN number on it and all, they sold our Rwd out from under us. I am so mad I could scream (wait, I already did that!) We are now forced to go with the 4x4 (from another dealership of course), so we'll be spending more than we planned, but at least it will be safer.

Thanks for everyone's input!

mannyboy

I have the 2001 4wd, for normal driving not using my 4wd where do I shift the H and L gear?, or do I have to leave it on Neutral.

bp3959

You can't use low in 2wd, if you try it'll switch on 4wd

russla

Well this is a little late, but I figured I chime in none the less

IMO, a true full time system is split 50/50 at the centerdiff. VC's that split the torque 90/10 or 95/5 are essentially an auto engaging Part-Time system (in other words, it just waiting to be locked, but not actually transfering any real torque until it's locked). They usually don't convert into a full time system, but rather transition into a Part-time system, as when slippage occurs, the VC is locked (or the electric diff is locked)

If the definition of a part time system is one where the output to the front and back is locked, then those systems with VCs or electric clutches typically meet that requirement temporarily (while engaged)

I bring this up because I feel the use of full time is very diluted.
Thanks for the vent space

wwest

Is one that CANNOT be used on a high traction surface without the high potential for incurring driveline damage.

Should only be used PART-TIME, as on a slippery/low-traction surface ONLY.

Traditional/historical definition.

russla

Yes, I don't disagree with the usage instructions, but the fact remains that the advice is given because there is no differentiation between front and rear, the shaft output is locked between front and rear, that's why it's part time. One expects that if you used such a "locked system" in a high traction condition, for long enough time period, you would bust something.

The systems that have all the power going to the front wheels, and then when slippage occurs the VC locks, are in fact locking the front to the rear, the same mechanical system effect as a manual part time system.

While it is locked only temporarily, it is locked. the rest of the time it isn't locked, and isn't transferring significant torque.

A full time system is just that, it's full time, and continually allows for torque and differentiation, so to call a system that auto locks and unlocks, full time is somewhat a misnomer. On demand, Real time, etc might be better descriptions for what are technically 2wd systems that switch into and out of a locked part time systems.

wwest

There's locked and then there's LOCKED.

Part-time 4WD systems as I have described FIRMLY and solidly lock the front and rear drivelines together.

An AWD system using a VC never fully locks. In the case of the Toyota AWD VC system, the HL, RX, etc, the VC never "solidifies" enough to carry more than about 25% of the torque to the rear.

Since a locked driveline would also adversely interfere with braking ability, and even make ABS non-functional, most AWD system that have more solid F/R couplings, Subaru for instance, actually disables the AWD system when you apply the brakes.

And yet another reason why many part-time systems can only be engaged in low gear and low range.

tlcman

I have explained this many of times... Using the simplest tems (maybe this time it will stick) the power is supplied to the trany.... then the transfercase....then to the center diff (this is from an FJ-80 which uses a very simple yet effective system) the center diff is always open (except for the new HL whatevers which as wwest pointed out have the VC and can only...ONLY transfer ~25% of the power depending on conditions) anyway, in my case the center diff was always open supplying power to the front and rear diffs according to the need of power.... When the truck has all fours on concrete with traction it has power to every wheel....when one wheel like the front right slips the open system would route all of the tourque to that wheel (in the HL it would give ~25% to the rear diff) In the case of loosing traction one could lock the center diff which gives a 1::1 ratio for the front drive shaft spin to the rear...that means 50::50 power distribution. That is a Fully LOCKED center Diff. Now if that front right tyre is still spining then the rear would have the same power....lets say the rear left tyre slipps....(this is a bad situation if you dont have lockers or recovery gear) One could at this time lock the front and rear differentials meaning that the power from the center diff split 50::50 to front and rear is once again split 50::50 to each wheel. meaning that the left wheel turns as fast but not faster than the left....follow??? this is a fully locked sytem. But mind you that when the entre system is unlocked it is still considered a Full time four wheel drive....

wwest

NOT referred to, or labelled "Full time all wheel drive...

Part-time 4WD systems typically, the clear majority of the time, run in "full-time mode", all three diff'ls (or two and a transfer case) unlocked, referred to as "open" in the case of the diff'ls.

Running in this manner all you really doing is carrying a lot of extra weight, bearing friction, and mechanical wear around, in preparation for the instances, sometimes few and far between, when you need to drive more that one wheel reliably.

TLC is correct in that if one wheel slips then ALL of the engine torque is routed to that one wheel. I would add that that wheel slipping LIMITS, severely, the level of torque the engine will produce, which is why the engine will instantly over-rev in this circumstance absent an experienced driver, or Trac.

But when you do need that capability it can be invaluable.

The multiple wheel drive market is, has now, evolved into two distinct segments:

Off-roaders...

Need/desire the ability for locking both diff'ls, front, center, and the transfer case which is of necessity for LOW range gearing.

These vehicles should ALWAYS be referred to as PART-TIME 4WD.

The core problem with these vehicles is this, when all four wheels have reasonably high traction the front and rear drivelines MUST therefore rotate at the same rate. It is NOT POSSIBLE for that to happen during a turn. When turning the front wheels always take a larger radius than the rear wheels. The tighter the turn the higher the difference is in the required rotational rate of the front driveline vs the rear.

Your typical off-roader is experienced with, and well aware of this aspect and simply shifts the vehicle out of part-time mode appropreately.

Since multiple wheel drive is highly desirable, on occasion, even for on-road and street use, the manufacturers are finding methods for doing this automatically, transparent to the driver.

Street use:

Most of these have already evolved, or soon will IMMHO, into vehicles with three open diff'ls and Trac. Trac is being used to apply brakes to slipping wheel(s) to force engine torque to wheels with traction.

There are other AWD methods in the market currently, but it might be best to refer all vehicles in this class simply as AWD.

Obviously you can combine these features in any mix you would like, AWD/Trac, and a true Part-time 4WD system, and some manufacturers have already done that. So what, how do we refer to those?

Trac has several MAJOR advantages. It can be programmed to "know" that the F/R disparate rotational rate is due to a turn radius and not wheel slippage, and it can "know" the rate difference is due to severe braking and thereby not interfere with the ABS.

tlcman

I agree with that and For the non off road enthusiast TRAC Control is great it is much...MUCH cheaper to manufacture and install than lockers and it will function just fine for light use. But for heavy use and frequent off roading it is not useful, an off roader would eat up their brakes very quickly if this were the case.

3toyboy

Any comments, or post referrals, concerning the pros and cons of a 4WD Tundra with a limited slip differential (and no VSC) versus a 4WD Tundra with Vehicle Stability Control (and no LSD)? Thanks.

tlcman

VSC only cuts the engine torque when wheel slip is detected (this means that your foot could be to the floor and the engine will only rev at 1,500 RPM, TRAC is the system that applies the brake to the slipping wheel, so if you are looking for a truck that will handle slippery conditions then the lsd is the one. And if you are an enthusiast then the LSD is a much better choice than the TRAC, if you take TRAC off roading allot you will eat up breaks and in some cases TRAC shuts down after being worked for extended periods of time.

wwest

several of the toyota models, Sequoia for instance, have AWD mode using VSC/Trac and also 4WD mode (first gear and low range selected)using locked center diff'l?

tlcman

but still VSC and TRAC are two different CPU controlled devices, VSC disengages when the transfer case is shifted into Low and the TRAC stays engaged. VSC can defeat the purpose of TRAC, VSC cuts the torque from the engine when any one wheel slips, thats all it does, Like I said, the accelerator could be to the floor, and the rpms could be at 1,500 thats what VSC does. TRAC uses a computer to independently control the brakes. If a wheel slips while both of these systems are engaged, the engine torque will be cut and the brake will be applied to that wheel.

cliffy1

I hate the TRACS system on the Tundra. Its great on a 4Runner and nearly as great on a Sequoia, but on a part time system, I don't like it. It requires you to actively engage it and it doesn't work at all in 4WD.

I'm just hoping the new model with the new engine coming this fall will have a system like the Runners have.

3toyboy

O.K. Cliffy, you may have tipped the scales away from the $1000-factory-cash-back/$300-dealer-cash-back/get the truck this week scenario, and pushed me to the wait and see/how long can I hold out mode. But wait, my 2nd Gen 4Rnr is out on the street with a For Sale sign prominently displayed. What decisions!

wwest

One of us......is.

I have understood that VSC, Vehicle Stability System, is used for directional stability ONLY. Using a combination of the yaw sensor and a steering wheel position sensor it will apply the front outside brake if over-steering is indicated, and one or both rear wheel brakes if understeering.

Trac, on the other hand, is using to simulate "virtual" LSDs, preventing any wheel or wheels with low traction from limiting the level of torque the engine can develop.

I guess I was aware that the Trac system does remain active during 4WD operations as I had advised someone that the ABS fuse could be removed to prevent the braking effects.

Has anyone yet tried this and does it still dethrottle (as well it might) even with Trac non-functional?

cliffy1

Ugh... I have not been on the sales end of this business for a while and had lost track of a few things so let me clarify a few things. I had to go to the owner's manual for this.

1. TRACS works all the time. In 4WD, it will not reduce engine power. The manual tells you to leave the system on during normal driving conditions which implies that you can turn it off, but there is no indication of how to do this. I'll have to find one on the lot that has it and see if I can figure it out.

2. VSC uses the engine and brakes to keep you from sliding sideways. It is automatically turned off when you shift into 4WD.

3. The "auto LSD" uses the TRACs system to mimic a limited slip differential. You have to tell it to do this by hitting the button on the dash. This looks stupid to me. I wouldn't bother with it. It seems like Toyota was trying to figure out how to use the TRACS system without going to a full-time 4WD system. More than likely, they think truck owners don't want a full time system and this ends up looking like a ridiculous set-up.

Personally, really hope they go to the Runner system next year. We're getting a new and bigger engine so hopefully, we'll get the new system as well.

bp3959

If you'd like to disable engine throttling and trac/vsc braking without loosing ABS you can unplug the fluid level sensor from the side of the brake fluid reservoir.

bp3959

Trac will indeed reduce engine power in 4wd(maybe you are thinking of 4lo), try putting it in 4wd and sit in some mud, floor the gas and watch how your gas pedal does nothing.

tlcman

TRAC does not...I repeat...does not cut engine power, all it does is apply brakes to the slipping wheel.
VSC is the system that cuts the engine torque, yes you could have the pedal to the floor and the engine is only at 1,500 rpm
TRAC does not cut the power from the engine, That would defeat the principal behind TRAC

bp3959

Well, according to toyota vsc is to keep the vehicle from sliding sideways, so if i lose my throttle trying to go straight it must be the trac. That wasn't my point though, which is that you will still get engine throttling in 4wd.

aggiedog

We're getting a new and bigger engine so hopefully, we'll get the new system as well.


Do you have any particulars on this new engine? Specifically, is there a new Sequoia on the horizon for 2005, or is it for the Tundra only first?

tlcman

Trac only uses the brakes so it might feel like you loose power but I guarantee you that the engine does not cut power that is VSC. I have worked on many TLC's with this option equipped, Trac has no control over the engine throttle.
For 2005 I have herd that there is a new TLC with a new engine, although I have herd that it is down sized engine 3.4 V6 but this is only speculation and rumor. If they go to a larger engine I would expect them to keep the V8 platform but go to a 5.7 litere or something that is able to run with the competitors.

biglatka

According to my owner's manual for the 2004 4Runner V6 (Pg.166) (for two-wheel drive models): the traction control system, "controls engine performance". It also states that "the VSC is always activated, even if the traction control system is turned off."

On Pg. 168 under "Active traction control (four-wheel drive models)" that statement (above) is missing and replaced with (first bullet): "The system controls the spinning of the 4 wheels. At this time the slip indicator blinks."

and the second bullet on Pg. 169 states: "you may feel vibration or noise in your vehicle, caused by the operation of the brakes. This indicates that the system is functioning properly."

then on Pg. 170 under VSC system it states that: "the VSC system helps provide integrated control of the systems such as anti-lock brake system, traction control, engine control, etc. This system automatically controls the output of the brakes or engine to help prevent the vehicle from skidding when cornering on a slippery road surface or operating steering wheel abruptly."

"This VSC activates when vehicle speed is more than 9mph."

Also on Pg. 161 on mutli-mode four-wheel drive models you can automatically turn off VSC by locking center differential (I know you all know this, I just put it here for completeness)

Hope this helps!

tlcman

Thanks Thats exactly what I was trying to say

sequoiasoon

The stuff I saw which seemed to be a very reliable source and confirmed by many dealers is same 4.7L but with VVT-i to bump up HP and Torque and mated to 5 speed auto from the Lexus. "Bigger" engine and more significant changes probably for the '06.

bp3959

I can tell the difference from the braking and engine throttling, and I can tell you for a fact then my Sequoia WILL throttle the engine if I loose traction trying to go STRAIGHT.

bp3959

Like you said, VSC is for sideways movement. So if the engine is being throttled down when trying to go straight it must be the TRAC system, and my Sequoia will throttle down the engine if I lose traction trying to go straight. Unfortunately on the Sequoia you can't lock the center diff without being in 4lo and placing the gear shifter(prnd2l) in Low, not much use if you have to use reverse and want the center locked, which would come in handy in the mud.

hank14

One would think that after 1444 posts, there would be very little debate over how these things work. I realize the technology is changing, but man! The only two things I am concerned about are:

1. How do I avoid getting stuck?
2. When I do get stuck, how do I get unstuck?

Fortunately, this has not been a problem in my Landcruiser (it almost never snows or rains where I live). I'm not posting this because I need advice, I'm just cracking up at all the confusion.

cliffy1

The Sequoia and the Tundra have completely different 4WD systems. When you said you had experienced this, I assumed you meant you had the Tundra with the automatic LSD which is the current topic of conversation.

3toyboy

Thanks Cliffy for keeping focused. From the responses so far, I've decided that for my applications, Tundras with real LSDs are preferable to virtual LSDs. I, too, hope that the current 4Rnr 4WD gear migrates to any upcoming new Tundra. My wife loves her 4th Gen Runner. I will play the wait and see game.

tlcman

VSC is designed to eliminate side skid by reduciung the engine throttle, this means that if you loose traction at one wheel and the engine keeps powering it then the car will side skid! this can happen when traveling straight. TRAC takes into account the speed of the engine to calibrate its brakeing movements but havs no influence on the throttle, none zip zero zilch nada.

wwest

TRAC should be used as a functional label ONLY.

Which, or how each ECU, computer, interacts to perform the TRAC functionality is not pertinent to the issue.

On the early Lexii, say my 92 LS, TRAC would almost instantly apply the brakes to the driven (rear) wheels if their rotation rate exceeded the front wheels. It would also INSTANTLY dethrottle the engine, even before the driver could react to the fact that the rear wheels had lost traction.

By the time we got around to the 2000 GS300 the dethrottling activity was delayed just long enough for an experienced driver to react and lift the throttle. The TRAC system would still activate the brakes instantly upon detecting slippage.

The TRAC system in my 01 AWD RX300 has yet another function, it will act as a virtual LSD, and in doing so if I am not quick enough reacting by lifting the throttle it will then dethrottle the engine.

The newer TRAC generation, the 04 RX, Sequoia, etc, is now used to allocate, apportion, engine torque for AWD systems that have three OPEN diff'ls, or the equivalent thereof.

The activation of TRAC in any "mode" will quickly result in dethrottling if the driver doesn't react quickly enough. If the engine were left over-revved for the conditions the brake rotors would quickly overheat and warp and serious damage might be done to the driveline, transmission, etc.

VSC:

If you are turning left, and/or the rear end is attempting to come around to the right (rear drive, LEAD foot), the VSC system will brake the right front wheel moderately and only momentarily, in an attempt to counteract the swinging moment of the rear end.

If the momentary braking action is successful all is well and good.

but if for some reason the over-steering is not fully counter-acted the braking action will cease before the majority of the mass of the vehicle crosses the centerline of the desired direction of travel.

Once the "tail" has swung too far out the braking action would tend to exacerbate the over-steering "moment".

If the vehicle is under-steering, not following the line set by the front wheels during a turn, the "inside" (inside the turn) rear brake is applied, or in the case of my 01 RX, both rear brakes are applied.

In the case of under-steering I would suspect if the condition persists then the engine would be dethrottled if the driver doesn't.

One further note.

The ABS pumpmotor is used to replenish the brake fluid pressure for all of these brake application/release(ABS) functions. It appears that Toyota/Lexus has put a timeout limit for continuous operation of this motor at about 45 seconds to one minute to prevent it from overheating and full failure.

For those of you relying on "virtual" AWD to get you out of that mud hole, you have ~45 seconds of AWD capability and NO engine over-revving capability at all.

Put it in first gear and low range (4LO??)BEFORE you get there.

tlcman

Systems change an until you work on one you wont understand

wwest

I would agree but with one exception. Having the shop manuals, reading them, along with other technical resources, and comprehending what you have read.

I've only "worked" on the early LS, changed out the entire TRAC pumpmotor/accumulator assembly on one, and had the brake fluid drained and flushed on two others due to intermittent TRAC diagnostic dash icon.

But lots of experimentation with the RX, first with a 2000 AWD, and now with the 2001. 4 wheel dyno, mudding, etc.

tlcman

this has gone on too long (almost 2 pages) and is aiming too personal for Edmunds, end of discussion

bp3959

Actually I thought it was quite a good discussion, and about time there's some activity in the Toyota sections. I have not worked on any traction control systems and only have my experience with it kicking into action to go by.

What I have observed is that it is very difficult to lose traction with these systems. I can punch the gas on gravel, mud, snow, or ice going straight or turning and the Sequoia will just go with no slipping. This cannot occur without engine throttling. My main complaint with Toyota is that they did not include an off button for this system in the 2001 Sequoia, and as anyone that's ever driven in mud knows, engine throttling will get you nowhere(yes I've tried, http://img33.photobucket.com/albums/v98/bp3959/, got stuck on my way to the mud because of engine throttling, turned it off and it would go through almost anything ). To disengage the system I have to open the hood and disconnect the brake fluid level sensor which will completely disable VSC and Trac until you turn off and restart the engine.

If the Tundra setup is different then I'm sorry for confusing things, I assumed they were the same. On the Sequoia there are three open diffs, with a locking center. To lock the center I have to go 4lo, and then put the transmission in low. Would have been nice if Toyota had given me a pushbutton to lock the center, which would make this system much more effective. A button to disable VSC/Trac would have been nice as well.

bp3959

On the Sequoia there are two buttons on the dash, one is for engaging 4wd, the other is to disable VSC while leaving Trac on(only works in 4wd). I can be in 4wd with the VSC disabled and still have to pull a wire and disable the entire system to stop engine throttling. I've been observing these forums for quite a while(and even read every past post in any forum I've found related to the Sequoia), I've seen you post very good advice and information and would normally accept your response as is but I truly believe you are incorrect on this issue with regards to the Sequoia.

biglatka

I too thought it was a rather good discussion. Although I've owned 4Runners (4WD) since 1986, I've learned much (from cliffy1, wwest, tlcman, and others) in this give and take about 4WD systems. A special thanks to cliffy1 for that great explanation on 4WD at the beginning of this forum. Let's keep it going.
Thanks again for all this good info!
___________________________________
2004 4Runner V6
1988 4Runner V6
1991 Miata (my fun toy)