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I still don't quite get it though. Here is the explanation by Cliffy:
"Highlander and RAV4 by cliffy1 May 16, 2001 (04:01 pm)
These utilize a limited slip center differential and open front and rear differentials. It is a viscous coupling center differential. If one of the front wheels begins to spin faster than the rear, the heavy liquid in the center begins to firm up which routes more power to the rear. Once torque is equalized, the 50-50 power split is resumed. This system is always engaged and requires no driver input.
It is possible to become stuck with this system. This is because of the open front and rear differentials. If both right tires were on ice, all power would be routed to these wheels."
In the RX 300 situation (picture), the front wheels are slipping, so why doesn't the viscous coupling in the limited slip center diff kick in to power the rear wheels and send the SUV up the ramp? It (the center diff) does kick in under high torque transfer conditons while normally driving to split the power 50/50 front and rear. Starting from a stop on dry pavement is a high torque low speed transfer....why does IT work and the boat ramp thing fails? And what if I am parked with my front wheels on solid ice and my rear wheels on dry pavemnet on a slight upslope? It would seem to me that the limited slip center diff would engage the rear wheels to push the vehicle out. What am I missing here?
You said that the center diff routes power to the least resistance....but isn't that the direct opposite of what everyone (else) says it does?
That is, the slipping wheels transfer power to the viscous coupling which then powers the NON slipping (higher resistance) wheels(s).
The Lexus fails the roller test (representing snow or ice on the road) because when the front wheels slip on ice the unmanaged center differential allows all torque to get lost at the front wheels (path of least resistance) rather than making any torque available to the rear wheels. Since the RX has an open front differential, even if one front wheel doesn't have traction, all of the power will leak out to that wheel. I remember one owner complaining about his '99 RX getting stuck in a ski resort parking lot, with only one front wheel spinning and the rest stationary. All of the power was being leaked out to that wheel only.
This is the reason why Lexus finally added stability control and traction control for the newer models. To help to combat this problem.
What about the Honda RT 4WD setup? Would that do better on the "ramp roller" test since the clutch pack would probably slip less than a viscous coupling?
How does the Escape/Tribute system allow a continuous AWD system to be locked?
Lastly, what determines "the limit" to which a limited slip viscous coupling will transfer power to the other axle (as opposed to letting it leak out the path of least resistance)?
(sorry for all the questions)
Les
Drew is correct about the limited slip center, but the chances of ever experiencing something as drastic as rollers on an incline are very remote. I have my doubts that ice could have the same impact. I played with this system last winter and was unable to duplicate the same effect. There was always enough traction to get moving, even on sheet ice.
I enjoyed reading your posts from this winter on the Highlander! I saw where the snow had shut down D.C. and you took the two AWD HL's (one with VSC and the other without) to the snow and floored them:)
I am eagerly awaiting my HL!
Les
I also know that there is no speed limiter. The warning label in the cab does tell you to keep it under 5MPH but I don't think you are restricted to this.
Because my store isn't near any dirt roads, I just have not had opportunity to experiment with this.
hopfully I can test it on my next testdrive. thanks again!
One other thing to consider is resale. I really don't know the SUV market in AL, but in general, the AWD version will do much better down the road.
I hope this helps. I don't think you can go seriously wrong either way.
A couple of weeks back I was decending a very steep road (in the White Mtns., CA). Due to the grade, I wanted to use engine braking and so I stopped the car, shifted it to Neutral, shifted the Transfer case to "low", and then shifted the gear selector to first. Started off and the car seemed to still be in "high". So, I applied the brakes to a near stop and the TC finally kicked into "low". All fine and well I assume. As I was going down the hill we saw a herd of Bighorn sheep. Wanted to take some pictures so I came to a stop, put it in park and set the brake. The TC was left in "low" When we resumed the decent I again noticed that the car was in "high". Again, I applied the brakes to a near stop and the TC automatically shifted to "low" - just as before. Just to test, I did the whole thing again (lower where the road was less steep) and got the same results.
So, why was the TC automatically shifting itself to "high". Neither of my prior 4wd Toyota's did this. When they were in "low" they stayed there. Does the fact that it is an auto tranny make it want to try to outsmart me? A dealer service advisor seemed flumoxed by my question so I have to wait for my regular guy to get back from vacation to ask again. In the meantime, you have any ideas?
Thanks,
HiC
I recently test drove a Tacoma Double Cab 4WD. The sales rep was new and it was just his 4th day on the job. I asked if there was any restrictions on engaging the High 4 slector. He said he wasn't sure. He then pushed the selector switch while we were on the test drive and at a speed of around 40 MPH on dry pavement. There was a slight jerking as if we had just hit the O/D button.
Reading an earlier post it was mentioned that on dry pavement it should not be engaged over 50 MPH, if I remember correctly. Could this have damaged the transfer case or drive shaft or caused any other damage to the 4WD system? Seems kind of irresponsible to have engaged the High 4 Switch if the sales rep wasn't sure what might happen.
we had dreamed about having a surf and test drove about 10 over 18 months, but it wasn't untill we purchased one that the dealer told us about this rule/trick? are we the butt of a joke? Great site!
Toadman. The selector will not engage until you drop below 50 (or 62 if it is a push button option) but once engaged, you can drive at whatever speed you wish. The danger of using it on dry pavement relates to turning corners and since you described no problems there, I'll assume it is OK. It sounds like you have an ill-informed salesman, but under the conditions you describe, I doubt there was any harm done.
Obrien. Back in the olden days, you did have to reverse 4WD vehicles to disengage the system. The 92 Runner had an "Automatic Disconnecting Differential" which means you don't have to do this. Your salesman was probably "old school" and made an honest mistake.
Drew
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Vans, SUVs, and Aftermarket & Accessories message boards
If I read correclty though, Obrien's 4Runner (Surf) was not a US import, but an AUS/N.Z import? It is possible that the ADD was not offered, or only offered as an option in that region. Quick question: does it have a live front axle or IFS?
Cliffy, I'll be driving my LC with one of the better service reps at my next service visit. Funky thing is that I have done some steep hill decents before and do not recall it auto shifting the TC. I'll let you know what I find out (in another month or so).
HiC
Japan exports some 90 000 cars a year. at one stage New Zealand was importing 75% of them!!
Check www.toyota.co.nz and look at "Signature Class" may also like to look at new cars/trucks as well -prices will amaze you guys.
naturally these imports have killed off car assembly here - Aussie still has the major car companies producing cars etc.
Also, these imported cars/trucks have warnings/instructions written in Japanese!!
Toyota makes available in Aus/N.Z multiple versions of vehicles that are simply not imported to the states.
The fact is, your market generally takes off-roading a bit more seriously than than the US market. The Land Cruiser is a typical example.
In the US we have one version: the 100 series with the V8 gas engine - all fully loaded with leather, sun roofs, etc.
In Oz, you have: 100 series: 3 engine choices (inc. a diesel), IFS or solid live axle (not on the V8), one or two petrol tanks, and all the "standard" stuff here are really options there. You also have thr 90 series with the same array of configurations including two wheel bases. All in all, 9 distinctive Land Cruiser choices compared to our 1.
Anyway, I would guess that in 1992, while in the US we had two choices (2wd or 4wd) and two engines (v6 or I4), all used the same chassis set up which included IFS. I am almost sure you had the option of a live axle front set up (same as on the pick-ups prior to 1989 here).
Finally, if you do have ADD, then you do not need to back up to disengage 4wd but it does take a least one full wheel rotation (forward or reverse) to disengage the auto locks.
enjoy,
HiC
Drew
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Vans, SUVs, and Aftermarket & Accessories message boards
Can VSC and TRAC be added to a 2000 4Runner Limited 4x4 equiped with rear locking diffrential? If yes, is it worth?
I do some off roading, but not serious. I'm thinking of adding these two safety features for my wife driving the vehicle.
Thanks!
FYI, if you live in the Central Atlantic Region, there is currently a $1000 rebate or 0% financing on the 2002 Runners.
Gary
The next question I have is to ask how you know the TRACS system was still operational. Was the indicator light flashing and did you hear the ABS clicking?
I am only asking this because I am curious. I'm not doubting you but I want to make sure I understand the conditions you were in. I would actually be happy to hear the TRACS works with the center locked as it would keep correct power left to right, but your description goes against my experiences and what I have been able to glean from the technical folks at Toyota.
The second time was about a week ago and I was climbing some ledges, once again in low, and was not able to get the rear wheels over the first ledge. I had decided the CDL wasn't very pertinent since the trac was on either way what would it matter? I wasn't getting up so I tried the CDL again, waited till the light came on, tried again and it pulled right up. Even after using the CDL switch I could still hear the tracs system engaging. I think I remember the trac indicator come on but I'm not sure.
Looking at page 122 in the owners manual it says that the VSC uses traction control to prevent skidding and that the CDL button will turn VSC off, but it doesn't say that TRACS is turned off.
I'm more than happy with my 4Runner. It's behavior is different than expected, but if the TRACS system is supposed to engage with the CDL, more power to me.
Gary
I've got an '99 RX300 AWD but does not appear to have a limited slip differential. Could you please tell me what the differences (perceived or actual) are with and without the LSD? Thank you.
Now, I believe I understand what you posted. So, if the front wheels slip then will the power be diverted to to the rear wheels? If so, how much power percentage-wise? And since my RX doesn't have the LSD, then will power be distributed evenly to both wheels?
Thanks again for all your help!
With as much as I have been able to learn, I am still a bit shaky on the LSD, both center and rear. I believe it is possible to exceed its ability to divert power perfectly. In theory, if the front axles are on sheet ice, most of the power would go to the rear. Once there, it would be split by an open differential that would bias power to the side with the least traction unless both had equal traction in which case you would have a 50-50 split.
I hope this helps. Drew, the host, may be able to add some insight here.
Of course, if you make the oil too hot, the viscosity reverts to its "natural" behavior and falls like a rock. Then you're in serious trouble.
Here's an article you might find interesting.
tidester
Host
SUVs
Maybe the 2001 is different, I don't think so, but will soon know the truth.
I am replace my '92 Ford Explorer (4WD w/LSD rear axle) and am looking at '01 4WD 4Runners. My main off-road use would be on beach sand. Question is, would normal 4WD mode work fine (with the traction control keeping things going if one wheel lost traction), or what are the circumstances were it would be desirable to lock the center diff?? If this does turn the traction control off, then it seems as if the open front and rear axles could create a problem...
Anyone have experience with a 01 or 02 4Runner on sand?
Thanks!
Mark
Open diffs on sand is not the killer you may think it is. Take a look at the other vehicles out there and you will see plenty of Toyota trucks doing just fine and every one has this arrangement.
As for when you would need to lock the center diff I've found myself a couple of times in a cross-axle position where three of wheels have traction, but one has so little traction(nearly off the ground)that all power escapes to that wheel, even with the traction control. When I locked the center diff it forced the front to turn as well and it pulled on out.
I've not had my 4runner on the sand but from what I've heard about traction control in the sand, it can hurt you on hill climbs where it impedes your forward movement.
Try this bbs for more info. http://www.outdoorwire.com/cgi-bin/ultimatebb.cgi?ubb=forum&f=13
Gary
I do plan to travel to the mountains during the snow season with the wife and kids. I also plan doing some light off roading to go fishing and or hunting.
The driving to the mountains and the light off roading can be easily handled by a 2WD but it would be nice to have the 4WD just in case. I used to have a Land Cruiser(got stolen) and that beast would go anywhere I wanted it to go.
The Sequoia is just bigger, and roomier than the LC and wonder if I buy the SEQ 4x4 would it be just as good as my old Land Cruiser.
I plan to keep this vehicle until it dies or I do. Any advice would be appreciated. Thanks.
Is the Sequoia 4x4 better, the same or just behind a LC 4x4 made from 2000 and newer?
Any information or articles on the Sequoia's offroad performance? I know that the LC is the benchmark for all other 4x4's.
Thanks for any information.
The only advantage the Sequoia has over the new LC is the ability to place it in 2WD if you wish. Other than that, they are the same.
As for off road performance, the LC may still get the nod due to a shorter wheel base and more robust front suspension. There was a TH member who posted a long and detailed description of his Sequoia's off road adventures. His user ID was slickrock. He posted it several months ago and it would take a lot of back tracking in the Sequoia topic to find it. He was VERY enthusiastic about its performance.
I bought a 2001 Sequoia Limited in March 2001. (20K miles so far - Mexico, Canada, California)
I think I understand the following:
This is a "Full time 4wd" which means it has a high and low set of gears, but also has a 2wd mode.
3 open differentials (front/rear/center)
Open differentials are reliable and relatively simple.
In 2wd mode the rear wheels are doing the pushing.
In 2wd mode if one of the rear wheels slip then all power goes to that spinning wheel BUT the computer applies the brake to that wheel to simulate a locked or limited slip differential (TRAC). In addition the engine is limited in RPM which can be annoying / dangerous depending on where you are, what you are trying to do, etc.
In addition variable skid control (VSC) is active keeping you from doing doughnuts in the parking lot.
In 4wd mode the TRAC braking is still active (to simulate locked or limited slip differential) but the engine is not limited in power or RPM, and VSC is still on. Because the TRAC engine rev limit is removed and the fact that 4 wheels are being driven, this is almost the preferred mode to be in, especially in anything than less than ideal conditions.
4wd has 2 modes - low and high. High is "fine for almost anything"
4wd low - with more torque going to the wheels - if you are in deep mud/snow/etc.
Question 1) Wouldn't 4wd low just get you into deeper trouble if you are stuck?
I am originally from the Midwest and the only time I can imagine using it is if there was a snow blade on the front of it and you want to push some snow any other situation?
4wd Locked - locks center differential so equal power goes to front and back (makes it into a transfer case). This is the only mode in which the TRAC braking is disabled. VSC is also off. Guaranteed to get equal power to front and back. But with the open differentials in the front and back it is POSSIBLE that if a wheel in the front is spinning, AND a wheel in the back is spinning, then all power will be to those spinning wheels and you are not moving. In fact keeping the 4wd unlocked may be preferred depending on which wheel(s) do not have traction.
In fact - assuming 4wd Locked would (presumably) only be used in extreme circumstances (at least some of the tires in the air). Then it would actually make the Sequoia into a front wheel drive if a rear wheel were spinning and a rear wheel drive if a front wheel was spinning.
I have noticed that it is possible to change the differential to an after market Locked differential if that was desired.
Question - would 4wd high be the first choice for a wet / slippery boat ramp? This would have lower torque to the wheels and hopefully not spin the tires as easily. If more torque was needed then 4wd low could be used(?)
If my understanding of the Sequioa is incorrect let me know, I really want to understand...
Thanks in advance!
Dean
As to your question of when to use the low gear range, it really would take something fairly extreme. Pulling another car out of a ditch, extricating yourself from a snow bank or a real problem at a boat ramp (such as a short steep ramp and your trailer tires dropped off the end) are about the only situations that the low gear range may need to be employed. I know you can imagine others scenarios, but you get the picture.
I can see little use for the center lock mode myself. About the only thing I can imagine is if you want to drift and slide in corners on dirt.
The steering wheel will kick back at you and you will hear the driveline windup and the tires scrubbing more and more as you tighten the circle.
Don't have any body parts, fingers, inside or through the steering wheel.