Toyota 4WD systems explained

wwest

It seemed to me that someone was thinkin of modifying their system so the center diff'l could be manually locked.

While I am sure that all of us are well aware of the potential for damage to the driveline in locked mode and high traction conditions, how many are aware of the problem with ABS?

Most, if not all, Anti-lock Brake systems are automatically disabled when the center diff'l is locked. If the rotation rate of the front driveline is "locked" to the rotation rate of the rear driveline then the front ABS can no longer function strictly independent of the rear ABS.

Potentially resulting in loss of control during severe or hard braking.

I suspect that to be one of the reasons Toyota is restricting the use of "hard" diff'l locking to 4lo and first gear only. One cannot need the brakes at a very severe level if no "speed" can be attained.

tlcman

Why would any one want to do that? Toyota assembles their trucks to Automatically lock when shifted in to the low gear selection starting with the FZJ-80's yes this disabled the ABS because if it didn't then mechanical failures could happen like damage to the center diff other diffs and the master brake cylinder, On the FZJ-80's the center diff locks when shifted into Low Transfer case setting the main trany shifter could be placed any where from P-1/L and the center diff would stay locked I'm not sure how they are configured now but people should not need ABS at below 35 MPH on dirt or slippery conditions, people should know how to "pump" their brakes. Plus when the Transfer case is in Low then the engine braking is max if you let off the accelerator like any person would when they hit the brakes the engine will idle down and slow the truck center diff locked or not.

steelcruiser

Sure you're not talking about being able to go into 4Lo WITHOUT locking the center diff? 80 series LCs can be modified to do this. This is a standard feature on the 100 series and I think some of the late 80 series had this feature too?

bp3959

It'd be nice to be able to have a seperate control for locking the center diff because when you get stuck it often helps to rock from drive to reverse and back, and it'd help quite a bit to be able to do that with a locked center diff.

steelcruiser

http://www.safari4x4.com.au/80scool/training/training.html

this has some good explanations about how and why. it's good reading and should help clear up some of this techno babble that's been going on

tlcman

Most LC's have a button that you can hit to lock the center diff in 4H , they started puting them on the late 80 series and continued through the UZJ-100's but I belive that it is optional. and wwest Im not quite sure what you are asking? Are You saying that on new LCs 4L will only lock the center diff if the Trany shifter is in Low?

gkatz1

Some of you guys are providing confusing info. information. 2001-2002 Sequoias will only lock in 4WD low with the tranny in 1st gear. 2003-2004 Sequoias will lock in low or high and in any gear. The lock button is in place of the old VSC button. This is a big difference and one reason I traded by 02 for an 04. I'm not sure what the VSC does when the center diff is locked

bp3959

I think it's about time to get a newer model. I'd like to wait for a larger engine though.

steelcruiser

It's standard on current 100s. Believe it's been standard on them since they were introduced.

You can go to Lo range WITHOUT locking the center diff.

wwest

Doesn't the Sequoia "4hi" simply put the front wheels "in gear" vs RWD only? It seems to me that I have read that anything other than 4lo and first gear, locked center diff'l, uses the TRAC braking system to apportion torque.

biglatka

The 2004 4Runner operates the same way. I can lock the center differential in either H4 or L4 with a push of the "center differential lock switch" on the dash. The VSC is turned OFF when this occurs.

bp3959

yup

gkatz1

Is this true for Sequoia also. I wasn't sure what the VSC does when locking the center diff.

bp3959

On the 2001 Sequoias VSC is automatically turned off when locking the center diff(which is only possible in 4lo and 1st gear) and possibly even in 4lo, as well as a button to turn off VSC(only works in 4wd). I'm not sure about traction control as I keep this disabled(had to pull a wire under the hood, no button to do this). From some earlier posts I get the impression that the center diff can be locked with a button on later Sequoia models(wish I'd waited) so I'm not sure what else they may have changed.

gkatz1

True, 2003-2004 Sequoia's can be locked by button in high or low.

bp3959

It's nice to see they came to thier senses, now if they decide to throw in a bigger engine I may have to trade mine in on a new one. The engine they currently use(4.7) simply has nothing from 1-3k rpms, if I could find a way to change that I'd be happy.

hank14

On my 99 Landcruiser, the ABS system does not turn off, even with the center differential locked in 4HI (full time mode) or 4LO (center diff always locked). It only turns off, as stated in the manual, when the rear differential is also locked, which can only be done in 4LO. The ABS light on the dash will come on when the rear diff is locked. Having ABS functioning, even in 4LO, is a nice feature, particularly on slow downhill movement over rocks and ruts, in these pre-downhill-assist models. The 98 and 99 uzj100 series Landcruisers, like the 80 series, do not have Traction Control (TRACS) or VSC.

Also, unless altered aftermarket, as Steelcruiser has discussed before, the center diff is always locked in 4LO. Apparently that feature can be disabled by unhooking one connection on the transmission or transfer case.

3toyboy

Sequoia & Tundra AccessCab - identical from the B-pillar forward, right?

AccessCab and DoubleCab - not identical from the B-pillar forward, correct?

WHY?? Isn't it more expensive for Toyota to make the DoubleCab dimensionally different?

steelcruiser

Hank-not sure when the center diff lock was introduced. I thought it was on some of the later 80s (96-97), but maybe not. I believe it's standard on 2000 and above, in conjunction with TRAC/VSC.

The "conversion" is pretty straight forward if you'd like to install this option.

wwest

That the only way to discuss Toyota AWD/4WD systems is to be MY and Model specific. Things are way to much in a state of FLUX!

Dropped by the dealer today and read the 2004 4runner owners manual. Nothing I've seen here adequately explains.

tlcman

Center Diff lock came standard on the early FJ-80's with the 4 litre inline 6 in 1993 mid year they put the 4.5 litre engine and the center lock stayed standard from then on. ABS was disabled when locked

logger

I am in Australia where the Highlander is known as the Kluger. A current article claims that the 2004 models electronic traction control will shut the vehicle down if it cannot cope with slippery or sandy conditions. Is this correct? If so what actually happens? Secondly is it possible to pull a circuit breaker to disable the traction control and revert to the basic AWD system via the Viscous coupling?

Article is at http://drive.fairfax.com.au/content-new/news/general/2004/06/04/F- - FXIOPX61VD.html

Quote:

"However, the middle-of-the-range model tested, the CVX, had optional electronic stability and traction controls that can't be shut down. The result is that when confronted with slippery or sandy terrain with which its electronics can't cope, it simply stops.

There are times when a bit of wheelspin is handy. Our Kluger refused to go up a steep test hill (the Widowmaker, near Alice Springs) which both the Territory and the Adventra were able to climb."

wwest

About Australia version nor HL for sure, but....

The 04 RX no longer has a viscous clutch, just three open diff'ls and a TRAC system which uses moderate or modulated brake application on the slipping wheel(s) to prevent wheelspin and thereby apportion engine torque to the wheel(s) with traction. If the driver don't react quickly to prevent "over-revving" the engine then the system will dethrottle the engine within a few seconds.

I have come to believe that the TRAC brake apportioning system has about a 45 to 60 second timeout to prevent the ABS pumpmotor from over-heating and burning out.

If this were a Sequoia I would advise you to simply slip it into 4lo and drive away. But if your Au HL has ther same drivetrain as the US 04 RX then you're simply stuck.

Or like me you can put 45mm wheel spacers all around, allowing 17x8 wheels and 235/65-17 tires and then you can use snowchains SAFELY on the rear only.

Toyota tells us under "CAUTION", first, that greater traction on the front than the rear can lead to loss of control, and then they advise us to us snowchains ONLY on the front.

Without the spacers snowchains cannot be used on the rear due to tight suspension clearance between the tire and strut.

In the past I have advised posters to disable the ABS pumpmotor to prevent the brake apportioning but I haven't yet any feedback as to whether this also prevents the dethrottling.

logger

Thanks for the detailed reply wwest. Gives me slightly better understanding of how the sytem works. Is disabling the ABS pumpmotor a simple process? (Pulling a circuit breaker or fuse for example). Interestingly the top spec model here in Aust comes with 225/65-R17 tyres however there is insufficient clearance for chains for the same reason you mentioned.

hank14

It certainly gets confusing trying to explain these things online. I'll speak only of my 1999 100 series Landcruiser. It does have a center diff lock switch. When put into 4 LO, however, the center diff lock is automatically engaged. After looking back through posts, I realized it was fj100 who mentioned a way to disable this feature.

And the ABS light does not come on (verifying that ABS is disabled) until the rear differential is locked via the optional electronic switch. My manual verifies this. Therefore, even with the center differential locked in both 4 HI and 4 LO, the ABS is functioning on my 99 LC.

wwest

be careful, be VERY careful.

The reason for ABS being disabled with the center diff'l locked is because otherwise the vehicle would be highly subject to loss of control.

The front wheels/tires expend ~70% of the braking HP, which means they rotate significantly slower than the rear, during braking at the level at which ABS would be useful.

If the center Diff'l is locked then the rear driveline must turn at the same rate as the front driveline. ABS cannot be effective at the rear if the slower turning front wheels are dictating rotational rate.

Some vehicles, mostly the ones with an electrically controlled AWD system, simply release the clutch which locks/unlocks the center diff'l during braking. Another approach is the way the Chrysler T&C AWD system works. The rear driveline has an integral over-running clutch so that the rear wheels can "over-run" the fronts during braking.

4WD vehicles which use a transfer case (for LOW gear ranges) typically use a dog clutch to lock the center diff'l. Dog clutches almost always take a few, if not many, revolutions of the driveline to engage or disengage, not quick enough to release effectively during braking.

hank14

How, exactly, am I supposed to be very careful? All I know is what I've experienced and read in my manual and repair manuals, as well as on-line. In 4Lo, the ABS light (meaning it is not working) only comes on when the rear diff is locked, as the manual says it is supposed to. Without the rear locked, I can descend down a steep rocky hill in 4Hi or preferably, 4Lo using the engine braking and the brakes, and they will not lock up, thanks to ABS. If there is a problem with that, it is in the design by Toyota, and I seriously doubt that is the case.

wwest

If some method isn't used to uncouple the drivelines during braking and the ABS isn't disabled when the center diff'l is locked, THERE IS A PROBLEM WITH THAT. But regretably, it will be your problem first, and then Toyota's only if your survivors chose to make it so.

But please be aware that you vehicle may have an over-running clutch or some other method of dealing with the problem.

steelcruiser

hank--you mean you can switch on the center diff lock in 4Hi, but not disengage it in 4Lo using the same switch? Hmmm.

wwest

The switch being referred to is from 2WD to 4hi, which engages the center diff'l coupling to the front wheels, but doesn't lock the center diff'l.

Just a guess.

hank14

Yes, the center differential lock switch is to go from full time 4WD with 3 open differentials (the way most 80 and 100 series Landcruisers are made) to conventional 4WD with the center differential locked. There is no 2WD mode on the Landcruiser. The center differential automatically locks when shifting the transfer case into 4 LO on 98 and 99 model fj100 series. This can be disabled, according to a previous post, by disconecting a wire going into the transfer case. The advantage of doing that is having the low gear range, but being able to turn in a short radius. I do not know how this works on 80 series or newer models.

These posts are from the Landcruiser board:

------------------------------------------------------------------ - - - - --
#2844 of 3807 Best Free Offroad Mod for 100 Series by fj100 Jun 30, 2003 (2:22 pm)
Hey guys,
The best FREE off road mod for the 80 or 100 series is having a driver selectable center diff lock. Go under the truck, unplug one wire on top of the transfer case, tape up the end of the wire and tape up the connector on the transfer case.

This mod allows the driver to select center diff lock in high range or low range. In low range with the center diff unlocked, the vehicle turning radius is just like normal. This is crucial in tight offroad spots with these large vehicles.

2 Notes

1. Do not forget to engage the cdl when in normal low range situations.
2. If your 80 series did not come with cdl button, it can easily be added. The switch is $50 bucks and the install takes about 10 minutes, just make sure you tape up the end of your flathead screwdriver before prying the dash apart.

Later,

Andrew

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#2845 of 3807 Center diff lock by steelcruiser Jun 30, 2003 (2:28 pm)
This is std on my ('02) 100. Didn't have this feature on my ('94) 80 though. It's a great feature.

------------------------------------------------------------------ ---------------
#2846 of 3807 gear lube by bryan28 Jun 30, 2003 (4:00 pm)
thanks for the tip! It looks like I have to pull the plastic under engine cover for the front. Thanks again, Bryan

------------------------------------------------------------------ ------------------------------------------------------------------ ------

Anybody confused yet?

Hank

wwest

I think I now understand why so many op for the simplicity of AWD non-interaction.

tlcman

Off-road tight corners still need traction to all four in slick situation, I see what you are saying but still there will be minimal to no vehicle damage if you have the center locked on a tight offroad turn with some loss of traction. Actually you can preform this on road and not cause too much damage (although I do NOT suggest doing it) Anyway, If you disable the auto lock mode then when you go into a tight corner off-road with the center diff open then you might get stuck in the corner. Locking the center then after you got stuck might get you out but you have decreased your chance. The Idea of lockers is locking them before you get yourself into a sticky situation, not when you are already in one. If you did not lock your lockers before you get there, but instead wait until you are stuck to lock them then you severely decrease your chances of independent recovery.
and yes I know that from experience! : )
Just scout out the corner before you go into it!

hank14

That's a good point, tlcman. It's interesting that my manual says to only use the rear diff locker function to get unstuck. (I thought its purpose was to help you drive further into an unpassable situation, thereby getting really stuck). Just kidding. I never could understand why 4WD folks would wait until they were nearly or actually stuck to engage their 4WD.

tlcman

1; with the lockers locked your speed is limited, above 10mph is not good for the internal components throughout the drive train.

2. some people say that it causes damage when it is not needed but locked, this is untrue unless you are wheeling on a surface with alot of traction i.e. oiled gravel ect. but in those cases there is not point in having it locked anyway.

But yes the lockers should be engaged before getting stuck, if their locked then you might just power through what you normally would get stuck in, therefore saving time, energy, and possibly the use of a winch.

stet

I have a '99 fwd Tacoma with standard transmission and full-time hubs. Toyota says that no Tacoma can be towed 4 wheels down. Sometimes a manufacturer will make these decisions for legal, not mechanical reasons. Can anyone give me a mechanical reason why I can't tow it behind an RV? If I were to do so, what transmission/transfer case configuration would be best (i.e. both in neutral)? I do not want to install a driveline disconnect like Remco sells.

sterndyke

As the previous owner of conventional 4WD vehicles (transmission, transfer case, front and rear differentials) I am leary of systems that shift between 2WD, 4HI, and 4LO electronically. The lack of a transfer case shift knob is troubling. I have looked at the 2004 4Runner that has electronic shifting for 4HI and 4LO. I found that these systems DO NOT supply the low gearing that I am used to. Also, I cannot find any information regarding gear ratios. What is the gear ratio for low gear 4WD on the 4Runner?

pschreck

Why would the lack of a manually moving lever be a factor in the gear ratio of a 4WD vehicle?

tlcman

Because you know that you have disconected it being that the lever is directly contected where as the button could reengage it upon vehichle shut down

pschreck

OK, so maybe you're engaged or maybe you're disengaged, but why would a manufacturer use different gearing in a truck with a lever versus a truck with a button? I mean, you either shift into 4hi or 4lo with a solenoid or a lever. It doesn't make sense to me that they would change the gearing for that.

I can believe that the connection to the lever would be more robust and reliable than the electric shift connection.

wwest

Low gear range in transfer cases usually involves the use of dog clutch, sliding spline shaft into a mating shaft/gear. The use of a lever gives the driver "feel" and thereby direct control of the clutch position.

Oftentimes the vehicle must be moved forward or backward very slowly to allow the splines to align and be driven "home".

PB electronics to do all of that automatically would get to be pretty complex.

For most owners the low range is used so rarely that it isn't worth the cost to the manufacturer to add synchomesh or other addaptions to overcome the nuisance factor.

blackandblue

That's why we got the RAV4. All the wheels, all the time.

wwest

"all the wheels, all the time......"

Toyota is very glad you think so....

nedzel

Huh? The question being discussed is electronic versus manual engagement of low range. Many vehicles have full-time 4WD in high range as well (for example, Land Cruiser, 4Runner, etc.).

pschreck

I agree. Eveybody needs to read #1495 again. sterndyke is saying that he gets lower gearing because a lever is installed instead of a button to engage 4WD Low. I don't understand why a manufacturer would make a transfer case with higher gearing just because of the manner in which it is engaged. Maybe there is a valid reason. I don't know.

nedzel

I don't understand why the engagement method (manual lever versus electronic switch) would impact the gear ratio. Sure seems to me that the 4wd low gear ratio on my 2003 4Runner is plenty low.

tlcman

Acts the same as a lever and fullfils the same purpose, it is quite possible that TOYOTA has changed their gearing.

zippercat

I want to drive my '04 Sequoia Limited on the beach, probably not to exceed 20 to 25 mph. All the discussions on here about locked this and that, frankly, are too much info for my feeble mind. Can anyone simply tell me what's the best way to engage the 4w for this situation? THANKS!!

bp3959

Try it out in 4hi first, if you have problems with it throttling the engine too much go 4lo to disengage the engine throttling. Don't worry about the Sequoia making it through, it'll do just fine(i've had it through much much worse).

stever

Just air down the tires and drive it right off the pavement :-)

SUV for Beach Sand

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