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What is so wrong about reading the owner's manual these days? And if you don't understand the owner's manual or it isn't as complete as you might like then for Christ's sake go and buy the shop manual.
You're buying a $35k plus vehicle, $200 for the shop manuals is a mere drop in the bucket in comparison and might just save you thousands upon thousand of $$.
Thank you
tidester
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SUVs
Thank you.
In the meantime the stuff over at 4x4abc.com is good reading.
The author also claims the RAV4 is of the "system 2" AWD type, but I am 90% sure it is the "system 1" in that power is always sent front and rear, unlike the Honda CRV.
This site also does contradict his claims on the RX300. Thanks.
Hey guys, I agree, every thing I have seen and read says the RX300 is 50/50 front/rear torque distribution. The only fly in the ointment is the disparate final drive ratio in the front vs the rear and I don't have enough mechanical background/knowhow to know what that means.
But the bottom line is that neither my 2000 RX300 AWD (without the MB version of TRAC and VSC) nor my 2001 RX300 AWD, with VSC & TRAC, would/will drive the vehicle forward with the rear wheels firmly on the ground and the front wheels not. They both would "drive" the front wheels with the rears elevated.
Or else you didn't take much time to look at the very first ICON/path on the 4x4ABC home page. but then if not how did you get to the second one?
There are four ICONs on that page and in my opinion they are all worth "following" and reading.
In the end it really doesn't matter you found and read what I intended anyway.
Thanks!
tidester
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SUVs
If you have larger circumference tires on the rear vs the front or vice versa then it might become VERY difficult to engage the lock, that's waht happened to my 92 Jeep when I replaced the rear tires and not the front.
"Why would I want to belong to an organization that would have someone like me as a member?"
Now THAT really hurts, cuts to the core.
Have I ever blamed/criticized Lexus for something of my own fault? Even partially?
That's just sirfile's quirky way of wishing you and gimpyrx a happy and prosperous new year!
Happy New Year, everyone!
tidester
Host
SUVs
Driving into the upper parking lot at the summit became a challenge, one after another I watched as vehicles had to give up the "climb", back down and turn around.
A Dodge/Chrysler FWD minivan was first, almost made it but then lost traction and never regained it. Honda Odessey next, even less success. Toyota HL, couldn't tell the model, didn't even make it to mid-point. Aerostar not only did fine there but went all the way up to the third parking area.
Our youngest grandson soon got too cold and my wife and I returned with him to the car. My curosity got the best of me so I cruised the lower parking area until a parking spot opened up within sight of the bottom of the first incline.
Lots and lots of vehicles couldn't pull the incline, most of them recognizably FWD. Quite a few vehicles did make it but some that didn't were quite a surprise.
An 01 or 02 (VSC badge) RX AWD. He was clearly having trouble on the incline but he wasn't going to give up easily. I finally got out of our car and walked over to help by pushing and of course this made him just a little peeved. He finally had to give up and back down the incline.
It was clear that his rear wheels were "driving", but apparently not enough to be of any help. I thought that I could also hear the TRAC "thumping".
But the real surprise of the day was a late model 4runner that couldn't pull the incline. That driver was REALLY peeved. He even put in "low" range before he finally gave up.
Absolutely no one seemed to have any trouble (driving, walking is another story)within the snow and ice packed LEVEL parking areas.
The incline:
Maybe 5% or less, and about 25 yards, packed snow and ice with some gravel and sand. We arrived late in the day, around 2 PM, and I'm sure the incline had been sanded early that morning but by now there was clearly more slippery surface than otherwise.
It was so slippery in the center that you couldn't walk on it without falling and I watched several kids slid down the center of the incline in their ski boots.
Why did the Aerostar do so well, equipped with simple summer tires, over others that shouldn't have failed? I don't know enough to be really sure but I suspect it was the fact that the Aerostar is basically RWD, 30/70, and switches to 50/50 if the rear wheels begine to slip.
But why didn't the 4runner make it? The driver was using a conservative approach, not gunning it like most would.
I'm wondering if this new type of LSD, using the brakes for implementation, just isn't up to these types of challenges. The reports I keep hearing is if you aren't carrying enough forward momentum when you hit a slippery area then you dead in the (frozen) water.
Is there anyone out there with this type of experience with the ML?
Yes, Cliffy WAS right.
I ordered the Sequoia owner's manual and shop manuals over the holidays, I want to be correct by Toyota's "standards". They could also be wrong, but I'll do my best.
That reminds me of an electrical engineer who once was asked, "how long after I apply the electrical power will the (LARGE) power supply capacitors be charged so the computer can command the machine bed movement?"
"Right away" was his instant, non-hesitating answer.
So the computer programmer wrote the control program to first, turn on the power, and then the next instuction, 200 nanoseconds later, commanded a machine movement.
At 60Hz it took about 300 milliseconds for the power supply capacitors to reach 90% of full charge. The engineer's answer was only off by a factor of 1,500,000 to 1.
I don't understand why you bought the shop manuals for the Sequoia. I was under the impression that you DO NOT own a Sequoia. At any rate I may order them too. Could you please post the publication number and the phone number to facilitate ordering for others who also might like to order these manuals? Thank you.
When someone asks a question on one of these threads that potentially has a safety aspect I will not guess at the answer. I think of buying the manuals not any different than buying any textbook, "book of knowledge".
As to your story of the 5% incline, I too am curious. It is my experience that many drivers haven't a clue as to how to properly operate their vehicles in the snow. Momentum is everything when dealing with extremely slick surfaces as you described. It is quite possible that you were the only one to hit it at the proper speed to make it up.
Over on CL GS thread there is lots of discussion about the need for a mechanical LSD in the GS430 vs the standard TRAC. On the GS series I have expressed my thoughts that the TRAC will always outperform a mechanical LSD. I have PSM on my AWD 911 and while I don't yet have very many miles on it I am pleased with the PSM so far.
But in listenting to some of the counter arguments I have begun to wonder if the electronic TRAC is really appropreate for an LSD replacement on an SUV.
I don't think I have EVER known of an SUV with an LSD on the front. It seems to me that the feedback to the steering wheel would be so severe as to maybe yank it from your grip (like a Jeep in part-time 4WD on dry pavemant). Lexus' has told me that the TRAC implementation on the RX is much more "moderate" than my 92 LS.
Maybe that's how they get around severe steering wheel feedback but I suspect that would also be pretty detrimenatl to AWD perfromance, especially if the RX always remains predominantly FWD biased, as I also suspect.
So for all that time, 87 to 99, I never knew why the full-time mode of the 4WD Jeep system was virtually worthless. I knew that often in adverse conditions I always had to go to part-time (locked transfer case, center differential{?}).
I probably wouldn't go to the trouble of buying the Sequoia manuals if you hadn't said it uses the same TRAC system for LSD substitution as the RX. Obviously that manual might help me understand my RX.
I have personally concluded, at least for the RX, that TRAC is only used right to left or vice versa. And maybe more moderatly in the front vs the rear due to the steering wheel feedback that would likely otherwise result.
Additionally, if TRAC were used to pro-actively allocate torque distribution front to rear then the longer time constant VC would be useless. However briefly, it needs a sustained disparate turning rate F/R in order to heat the viscous fluid and thus increase the coupling coefficient across the VC, itself across the center diff.
Both the RX and the HL have an open, free, center differential, actually all three diffs are of this type. Across the center diff is a Viscous clutch, coupling, which is supposed to limit the "freedom" of the center diff if its two outputs develop a disparate turning rate.
Becuase the RX never acts like an AWD, always "acts" more like a FWD than anything else, I have come to suspect the VC is there for marketing purposes only, it doesn't have enough "pre-load" to actually have any affect on drivability on LTS, Low Traction Surfaces.
I came to this conclusion after reading the implementation details of the Chrysler T&C AWD system.
Chrysler says that since the front wheels do 80% of the braking there cannot be a VC, at least not a "tight" one, between the front and rear during severe braking when the front wheels are likely to turn at a substantially slower rate than the rear. "Telegraphing" the slow front roll rate to the rear through a tight VC coupling, or a VC coupling that quickly tightens with disparate F/R roll rates, might brake the rear wheels to so great a level that the driver loses control of the vehicle.
So Chrysler's VC is bypassed by an over-running clutch so the rear wheels can over-run the front during severe braking.
But that's not all.
So that the T&C can remain an AWD in reverse gear when otherwise the over-running clutch would open the driveline to the rear, Chrysler adds a "dog-clutch" to lock the front and rear drivelines in reverse.
Now, this is Chrysler, CHEAP, inexpensive, shoddy designs, that has gone the extra mile to assure their customer's safety and provide a truly multi-mode AWD.
Now do you see why I suspect the RX's VC isn't really functional?
I am with the impression that HL and RX (also RAV) has a center differential with 50/50 torque split and supplemented with VC (mild version?) to limit front to rear wheel speed difference. Torque is always distributed to all wheels at all times.
I believe Chrysler (and Volvo?)has no center differential, just VC to connect the front to rear axles. Torque here is fed to the front and if the front slips, the VC catches up and send some torque to the rear. Others has a VC substitute such as that of GM versatrac, MDX and CRV.
Just my $0.02.
But the T&C and the RX AWD setup is VERY simuliar.
Both have three open differentials, front, center, and rear. Absent the VC, what that means is that as long as all four wheels maintain something approximating equal traction the engine torque will be distributed accordingly. But if one wheel, or wheels, begin to slip, then ALL available traction will be routed to the wheel or wheels with LEAST traction.
The T&C shop manual is very explicit and detailed even including a good theory of operation and some cause and effect, and even some engineering background regarding implementation decisions.
The RX shop manuals, on the other hand, seem to be written as secretively as is Lexus "HELPS" about the overall operation of their system.
So the Chrysler first.
The Chrysler's VC is placed in series with the rear driveline. Chrysler says that its initial pre-load, which determines the VC's coupling coefficient in latent (no wheelspin) mode, is high enough that during severe or even moderate braking it might "telegraph" the slower turning heavier braking duty front wheel's rotational rate to the rear wheels, defeating the ABS at the rear which might lead to rear wheel lockup and loss of control.
Obviously things would quickly get out of hand with sustained severe braking, say on a ice covered slippery roadbed, when the VC reacts by further increasing the coupling coefficient.
So Chrysler has placed an over-running clutch around the VC so that the rear wheels can freely over-run the fronts in these situations.
Given the dearth of detailed information about the RX AWD setup some of what I say about it is something more of a guess than actual knowledge.
What I finally did was enlarge the pictorial from the RX shop manual of the "transfer" gearing in the area where torque is split front to rear. I'm sure I can state as factual the issue of an open differential for basic F/R torque split.
What remains somewhat fuzzy to me and others is the placement of the VC in this mix. Several mechanical (but with no automotive experience or background)engineers believe the VC is mechanically coupled ACROSS the center differential and others think it is more like the T&C. It is clear to me that the answer cannot be readily determined From the enlarged drawings and Lexus refuses, so far, to clarify the issue.
Regardless it is clear to all that there is no over-running clutch. The only conclusion one can derive from this is that the RX's VC never reaches a high enough coupling coefficient to affect the need for ABS at the rear. Either that or Lexus doesn't care about our safety and I can't, will not, given the evidenceto the contrary below, accept that as an explanation.
Shade-tree testing. Done on both a 2000 AWD RX and a 2001 AWD RX with VSC and TRAC.
With the rear wheels off the ground on a roller jack and the front wheels chocked against forward movement and the transmission in drive and the engine RPM increasing slowly and carefully the rear wheels would spin freely and the front wheels would rise higher on the chocks as engine RPM rose. I was too scared (timid?) to get much above engine idle, didn't even reach 1000 RPM in this testing mode.
In the opposite configuration, rear wheels chocked, etc, I could raise the engine RPM all the way to 2000 with no perceptible effort by the rear wheels to climb the chocks, and the front sspinning rapidly.
Then:
With all four wheels elevated.
First I blocked the rear wheels from turning with 1x2" strips of light duty lumber, allowing the fronts to turn freely. In drive mode with RPM as high as 2000 you could hear the wood being stressed but no breakage.
In the opposite configuration the 1X2" strip blocking the left front broke just as soon as I raised the throttle above idle.
As far as I could tell TRAC was never activated and certainly there was no indication of same. I could cause VSC to come alive by turning the steering wheel off-center as I raised the engine RPM.
Then New Year's day I watched an AWD RX with VSC fail to climb a 25 yard 5% incline of packed snow and ice that my AWD Aerostar had no trouble at all getting up. I also watched as a new 4runner failed to get up this slope.
To be fair most of the vehicles that tried didn't make the grade, maybe only about 10% did. When I offered to help the 4runner driver by "pushing" (manually) he seemed to get fairly peeved. He even tried it in low range with no success.
Come to your own conclusions.
http://www.howstuffworks.com/differential7.htm
Initial coupling coefficient is determined by latent, non-heated, viscosity and apparently this parameter is most often "set" by controlling the "size" of an air bubble within the hermetically sealed VC assembly. Until this air bubble is completely compressed, virtually non-existant, the increasing VC fluid volume within the chamber due to increasing temperature will not result in an increase in the coupling coefficient.
The second parameter has to do with the formulation of the fluid, how fast will the fluid's volume increase with rising temperature. The faster the fluid "expands" with rising temperature the higher is the "rate of attack" of the VC.
It appears to me that the RX's VC chamber may be filled with air and not much else.
With the rear wheels spinning freely and the front not slipping, it indicates that it has a center differential. Otherwise, if it is just plain VC it would require the front to slip first before the rear starts spinning.
Your subsequent experiment would indicate that the VC on the RX's center diff biassed to one direction.
Here's an interesting and really informative article but a bit dated.
http://www.eskimo.com/~eliot/awd.html
Happy reading.
I hope I am not irritating you.
So when the VC was announced some years ago that seemingly relied on fluids acting inverse to this law I was taken by surprise. But in the end I figured that some scientist had figured out a formulation to create this affect, increasing viscosity with increasing temperature.
Now I can't say for sure that the above revelation was wrong, but after recently reading a fair amount about VC implementation and design I have come to believe that VCs actually operate in the following way.
The two sets of clutch plates and the viscous fluid are placed in a fixed volume sealed chamber. The fluid, silicon normally, is specially formulated to dramatically increase its volume (all{?}fluids expand with temperature) with just slight increases in temperature.
So, what we have is a VC wherein the viscous fluid "effectively" increases it viscosity but what is actually happening is the fluid "pressure" within the chamber is what is actually doing the work, increasing the coupling coefficient between the two sets of clutch plates.
Really only a guess based on the way manufacturers control the actions of a VC, air bubble, etc.
Not at all, I need all the help, input, I can get.
As I said the RX has an open, free, center differential, just like the front and the rear. The center differential seems to be configured very much like the pictorial you linked.
Except some of us think the VC is mechnanically mounted ACROSS this center differential, coupling its two outputs, thus limiting its "freedom" if the wheels if either output begin to slip. Others of us think the VC is simply in series with the center differential's output to the rear driveline, just like the T&C.
Even enlarged, the RX's pictorial representation can be readily interpreted, argued, either way.
In any case it is pretty clear to me, based on my testing, that the RX AWD, even with the VC fully "activated", remains primarily FWD torque biased. But none of us have been able to determine, from the information available, how this torque bias to the front is accomplished.
The more expensive one have more numerous discs and rely primarily on "viscous drag" for locking effect.
I think the increased viscosity with temperature doesn't have much to do with the pressure, though it's a good guess!
It was discovered that the behavior of a viscous fluid can be the reverse of what is expected (newtonian fluids) by the addition of certain polymers to the fluid. I think it has to do with the unraveling or stretching of the polymer molecules as the fluid is warmed.
tidester
Host
SUVs
Just what I believed until I ran across the actual VC manufacturing process. They actually do control its performance "on-set" by injecting an "air-bubble" of a specific size depending on the level of coupling coefficient they want vs increases in temperature.
Perhaps there is more than one way to skin a cat.
I have considered finding someone to "re-build" the VC in my RX so it does a better job of reacting to wheelspin and more quickly and firmly distributes the torque. But in the interests of safety, my own, that would likely require that I add an over-running clutch like the Chrysler T&C.
So I guess I will, for the moment, live with an RX300 AWD that isn't.