Last post on Aug 21, 2013 at 5:16 PM
You are in the Toyota Sequoia
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Toyota Sequoia, Toyota Highlander, Toyota 4Runner, Toyota Land Cruiser, Toyota RAV4, Toyota Tacoma, Truck, SUV
#2179 of 2493 Re: RAV4 .vs. Subaru AWD [hdfatboy]
Mar 31, 2008 (6:30 pm)
In the early sixties when LSDs were just beginning to become available I happened to live in North Central Montana, so yes I have lots of experience with both mechanical LSDs and virtual ones.
Going back a few years we lived up in the woods (Seattle eastside) at the end of a two mile dirt and gravel road (mostly dirt [MUD!!] for the last mile or so) with several fairly steep inclines. That is when I began my second experience with LSDs. We purchased a 1985 Jeep Cherokee LTD to be sure we could get in and out of that road in all conditions. It took chains on all four wheels several times but we always made it through. I later traded up to a '92 Jeep Cherokee LTD with the same RWD/AWD/4WD/rear LSD capabilities as the '85.
In 2000 the '92 was retired to the ranch in MT (still "going" strong even today) in favor of a '00 AWD RX300. The '00 RX was shortly traded in for an '01 AWD RX300 that had HID, GPS/nav, VSC, Trac etc. Like the '00 the center diff'l of the '01 has a VC, viscous coupling, to "stiffen" the otherwise open center diff'l when disparate F/R wheelspin/slip develops.
Oh, whereas the '00 RX had a mechanical rear LSD the '01 RX uses TC to implement a virtual rear LSD. As a matter of fact the center VC turns out to be dead weight since TC also implements a center virtual LSD. The VC was dropped from the RX series beginning with the 04 model year.
My '01 911/996 C4, which I drove home in 4" of snow just the other night, has a TC (PSM) implemented virtual rear LSD of which I am very pleased. Currently there seems to be a lot of 911/996 owners who have added a mechanical LSD without realizing they need to find a way to disable the virtual one otherwise the mechanical one is just dead weight.
And I would be VERY surprised if the ML320 or BMW X3/5 has anything but a
"Name a high end performance sedan or a serious AWD or 4WD vehicle that doesn't..."
Frankly I don't know of any high end performance sedan that I can say for sure either way...except for Lexus using the virtual one but that's just another Toyota. But I serious doubt that it matters to those buyers one way or another, or if they even "know".
IMMHO there is NO SUCH thing as a "serious" SUV with AWD and not 4WD or 4X4 mode also. No self-respecting "serious" SUV would stoop to that level. But I will grant you that if it has a 4WD or 4X4 mode then it is marketed, at least partially so, to the off-road crowd and therefore it very likely has a mechanical rear LSD.
Be advised that I am in no way denigrating mechanical LSDs, just that they have their place and that is NOT in a general public market vehicle.
I wonder if the PSM equipped Porsche Cayenne has a mechanical LSD.....I think probably not.
Now, there is ONE SERIOUS 4WD SUV...!!
But useless, overall, as teats on a bull.
#2180 of 2493 Re: RAV4 .vs. Subaru AWD [wwest]
Apr 01, 2008 (7:04 am)
Good discussion to better understand LSDs and their value .
"In 2000 the '92 was retired to the ranch in MT (still "going" strong even today) in favor of a '00 AWD RX300. The '00 RX was shortly traded in for an '01 AWD RX300 that had HID, GPS/nav, VSC, Trac etc. Like the '00 the center diff'l of the '01 has a VC, viscous coupling, to "stiffen" the otherwise open center diff'l when disparate F/R wheelspin/slip develops.
Oh, whereas the '00 RX had a mechanical rear LSD the '01 RX uses TC to implement a virtual rear LSD. As a matter of fact the center VC turns out to be dead weight since TC also implements a center virtual LSD. The VC was dropped from the RX series beginning with the 04 model year."
The 2008 Lexus RX AWD has a center LSD (VC) and an open rear differential. (Its a Toyota and I don't believe Toyota uses a rear LSD in any of their vehicles including trucks, which I believe is a competitive mistake.)
"My '01 911/996 C4, which I drove home in 4" of snow just the other night, has a TC (PSM) implemented virtual rear LSD of which I am very pleased. Currently there seems to be a lot of 911/996 owners who have added a mechanical LSD without realizing they need to find a way to disable the virtual one otherwise the mechanical one is just dead weight."
All versions of the 2008 Porsche 911 (Turbo, Carrera, GT3, Cabriolet) have a mech rear LSD. Various models can be upgraded to include an auto-locking rear diff.
"And I would be VERY surprised if the ML320 or BMW X3/5 has anything but a
"IMMHO there is NO SUCH thing as a "serious" SUV with AWD and not 4WD or 4X4 mode also. No self-respecting "serious" SUV would stoop to that level. But I will grant you that if it has a 4WD or 4X4 mode then it is marketed, at least partially so, to the off-road crowd and therefore it very likely has a mechanical rear LSD."
By "serious" AWD I simply meant with sophisticated awd designs meant to manage all available power to avoid slippage. Toyota's approach is to generally reduce the power through engine management to compensate for slippage (in addition to transferring some power by brake management).
Audi, Subaru, GM and others take the approach of more agressively transferring torque through the use of mech LSDs to find a non-slipping tire with a less agressive engine management to reduce power. I prefer to manage the power as a driver and want the vehicle to figure out which wheel can best utilize that available power. Toyota assumes the driver doesn't know what's best and decides for them through more agressive engine management.
"Be advised that I am in no way denigrating mechanical LSDs, just that they have their place and that is NOT in a general public market vehicle. "
"I wonder if the PSM equipped Porsche Cayenne has a mechanical LSD.....I think probably not.
Now, there is ONE SERIOUS 4WD SUV...!!"
I'm not sure I would consider the Cayenne a serious suv however it is certainly a serious performance vehicle. The 08 Cayenne has a center LSD and a rear mechanical auto-locking differential.
Here's a few vehicles and what their designers thought were the best designs for traction and power distribution:
2008 MB ML & GL uses open diff. designs plus the ABS brakes to transfer torque. They can be upgraded with locking rear differentials. If you want the AMG versions, both models will be upgraded with limited slip rear differentials.
2008 BMW X5 comes with a ctr LSD and an open rear diff. You can upgrade to a rear LSD for $625 and all M versions of any BMW come standard with a rear LSD.
2008 Subaru Forester, Outback, Tribeca, Impreza all have mech rear LSDs and a ctr LSD (VC).
2008 Audi Quattro's R8, S8, A4, A6 have mech rear LSDs.
All of GM's Full size suvs either have a rear mech LSD or offer it as an option including the new Tahoe Hybrid which comes std with a rear mech LSD.
I think I've shared that there are many on-road vehicles with mech LSDs and in fact most of the higher end vehicles either come with mech rear LSDs std or offer them as options.
#2181 of 2493 Re: RAV4 .vs. Subaru AWD [hdfatboy]
Apr 01, 2008 (12:58 pm)
"The 2008 Lexus RX AWD has a center LSD (VC)...."
When the RX330 first came out all of the maketing materials, printed and inline, indicated it had, like the previous RX300, a VC, Viscous Coupling, across the center open diff'l.
It did not and I have an email from Lexus corporate agreeing with me and apologizing for the miss information.
Now all of the maketing materials for the RX350 indicates it uses the VC.
It does NOT...!
I have opened email discussions with Lexus about this falsification on three separate occassions. Each time I am asked to convert the discussion to verbal via telephone and each time I have ended up being told that I will recieve a retrun call with a definite answer with 48 hours. No such return call has ever been made.
The NCF, New Car Features, at techinfo.toyota.com, for the first model year of the RX350 indicates a return to the MF2AV transfer as was used in the RX300. But all of the other documentation, repair manual, etc, for that same initial model year and all following years indicate that the MF2A transfer is used. A search for the term MF2AV for any RX350 model year yields no results whereas a search for MF2A
in those years yeilds dozens.
In addition I recently tried to buy a new VC "canister", from an online source I often use for Lexus parts. I gave a valid VIN number for a 2008 AWD RX350 but got no response. On the same day I ordered parts, same online source, for my 1992 Lexus LS400 and got a response within 24 hours.
I don't have a clue as to why Lexus might or maybe would be falsifying, continuing to falsify, marketing information about the AWD RX series in this way.
#2182 of 2493 Serious AWD & Engine Dethrottling.
Apr 01, 2008 (1:16 pm)
Given what I see out in on the public streets when the weather turns adverse, snow covered, icy roadbeds, I'm not so sure anymore that quick dethrottling isn't a good idea, a DAMN good one regardless of the drive method.
Look at it this way, even if you are driving a 4X4 what would any experienced or knowledgeable driver do if all four wheels began spinning on ice or packed snow due to the lack of enough traction to move up an incline.
You'd STOP what you're doing, scratch your head and say "what can I do to add more traction?"
But how do we begin to get the general public to understand that, absent it being FORCED on them via engine dethrottling..??
Yes, spinning your wheels will often help to get you up and moving initially, but what I seem to be noticeing is far too many drivers simply "burning rubber" with little or no hope of moving up even the smallest of slippery roadbed inclines.
So, what I see coming, soon, is that all vehicles will have a dethrotting "feature" to prevent such actions by unknowledgeable and/or inexperienced drivers.
I often see circumstances wherein NOTHING will get a vehicle moving forward, not even a 4X4 drive system, other than when equipped tire studs or tire chains. And in that case, studs or chains, RWD will often easily suffice.
I am totally opposed to tire studs as a result of the damage they do to our highways when they have no use anyway, so I always carry a set of tire chains, two during the winter months.
#2184 of 2493 Re: RAV4 .vs. Subaru AWD [hdfatboy]
Apr 01, 2008 (4:19 pm)
Well, first of all they quite clearly falsified this claim for the RX330 series and I can provide you with a copy of the email making the admission.
There is little need for referencing publications other than Lexus themselves as it seems quite clear to me that Lexus would be the base source of such information.
Now go back and read the very first paragraph under the bold title:
"Full-Time All Wheel Drive with Vehicle Stability Control."
But first, let me tell you that lots of Porsche 911/996 owners have gone out and installed mechanical rear LSDs onlyto discover them to be totally non-functional usless a way can be found to disable the factory supplied "virtaul" LSD using traction control firmware.
VCs, couplings or clutches, are not instant acting. The VC in my '01 AWD RX300 takes tens of seconds to stiffen enogh with sustained wheelspin/slip before it will convey even 20% of the engine torque to the rear driveline. But the reality of the matter is that even the VC in my RX300 is completely non-function for real world aspects.
The TC, Traction Control, system in my '01 will instantly apply braking to any wheel or wheels that slip due to engine torque and just as quickly dethrottle the engine. Apparently teh RX330 and RX350 will do the same thing. The only real difference being my TC dethrottles the engine via EFI control, fuel starvation, whereas the others have DBW, e-throttles.
But read the paragraph that I referenced and see if you can make any sense of the wording. For me, the described operation of Trac makes the viability of having a functional VC non-functional.
#2185 of 2493 Re: RAV4 .vs. Subaru AWD [wwest]
Apr 01, 2008 (7:48 pm)
I'm not following your logic. First... do you agree that the 08 RX has a viscous center LSD? You can't really believe that a mistated email that WWest received is somehow more reliable and accurate than the Lexus website AND the formal launch press release which went through significant copy control and legal review before publication?
Of course mistakes do happen, however even if the website was mistaken at first the lawyers would have required a correction immediately. Since the Lexus website clearly states that the new RX has a ctr LSD and it has been on the website since launch (nearly 6 months), I think most reasonable people would agree that the new RX includes a viscous ctr LSD in the absence of physical proof or a reputable source that suggests otherwise..
I see no conflict between the software advantages of "selective braking" and LSDs in a drivetrain. In fact, its really the best of both worlds. By incorporating the LSDs you get real time torque transfer at the moment its needed without any speed limitations, wearing of brake pads, potential warping of rotors or overly agressive engine power reductions.
The physics of an LSD manage the torque transfer seemlessly across the various corners. By having an LSD in the center and the rear, it enables the software developers to dial back the VSC and TC to levels that would only be activated if the LSDs were overwhelmed by speed, traction, torque transfer, driver error or some combination. This would make the VSC and TC the safety features they were originally intended to be instead of a cheap man's version of a mech. LSD.
The very best high performance vehicles and the best AWD systems layer the mechanical approach with the computer approach to maximize torque from the engine being distributed to the tires that can best use them. If the power is more than can be distributed than the safety features of VSC and TC step in to protect the driver.
That's why you are probably correct that the guy's adding LSDs to vehicles like 911s that had open diffs with VSC and TC may be wasting their time unless they disable the VSC or modify the programming to acommodate the LSD. That's why its best to have the LSD from the factory if the vehicle has VSC and TC.
That is my personal preference and the best vehicles in the world take that approach to torque management. Toyota attempts to jump straight from "torque management" to "driver management" by skipping the physics of an LSD (as well as the cost advantage) and instead use software to manage the driver.
Toyota did make some progress in their thinking by inserting ctr LSDs back into their drivetrain lineups for many of their models in 2008. Now they just need to catch up to the best manfuacturers of 4wd and AWD vehicles by adding rear mech LSDs, at least for their premium products.
#2186 of 2493 Re: RAV4 .vs. Subaru AWD [hdfatboy]
Apr 01, 2008 (9:55 pm)
First, again, if you are able to get your hands on an early, first year, RX330 sales brochure you will find that it "touts" the fact that the RX330 has a VC. Not so with the brochures for the following years of the RX330. And as for this matter, no VC for the entire RX330 product run, is quite well documented at techinfo.toyota.com.
I really can't speak, directly, for an RX model but my own. On a packed snow or icy parking lot my RX's Trac system will quickly abort even the slightest level of wheelspin/slip due to engine torque. The brakes are almost instantly applied and the engine is dethrottled via fuel starvation. MY '01 does not have DBW so at first I didn't know how the dethrottling was accomlished but the shop/repair manuals for my '01 indicate it is via fuel starvation.
Viscous clutches and couplings do not react anywhere near instantly to desparate rotational rates at the two inputs. That's actually their greatest advantage in this particular application. There is very little VC functionality to interfere with the need for the front wheels to be free to rotate independently of the rear when turning. The onset of VC "stiffening" depends on the formulation of the viscous fluid, basically how fast its volume (tries too) expand due to the heat of "stirring".
If these is no ability for sustaining an extended period of disparate rotation of the two inputs to the VC then the VC will never become functional.
This, the above, is the basis for my firm belief about why the VC was dropped for the entire RX series with the introduction of RX330 model and is also not used on the AWD versions of the Highlander and the Sienna, although otherwise those AWD drive trains are an exacting duplication of the RX.
But, I remain quite willing to be proved wrong.
But the evidence available to me so far indicates, weights heavily, on the side that Lexus is intentionally misleading the buying public.
As to "why", my only answer would be for you to study the Japanese culture.
#2187 of 2493 Re: RAV4 .vs. Subaru AWD [wwest]
Apr 02, 2008 (9:52 am)
I'm still perplexed by your references to past RX models. My original comment was specifically focused on the 08 RX which I stated has a viscous center limited slip differential. Your view was that I was incorrect and that the 08 RX 350 has an open open ctr differential. Do you now agree that the 08 RX AWD has has a ctr mech viscous LSD?
My experience with viscous ctr LSDs is far different from yours. My recent experience is with GM's viscous ctr LSD and Toyota's Torsen ctr LSD. The response time of the viscous LSD in the GM Denali AWD is literally measured in fractions of a second as stated in their literature. You can actually feel the difference in a vehicle with a dedicated power distribution compared to a vehicle without a dedicated ctr LSD. For example, when accelerating through an off-on ramp you can actually feel the Denali "pulling" itself in addition to "pushing" itself through the curve.
By having a ctr mech LSD the manufacturer can dedicate a certain % of power to the front wheels without having to worry abound binding in sharp turns. That's why the Tundra's 4wd system is parttime and the Sequoia's is full-time (Tundra has no ctr diff and the Sequoia has a ctr torsen LSD). A 4wd system or AWD system that does not have a ctr LSD cannot distribute torque with minimum power requirements which is a significant disadvantage for 4 wheel drivetrains with open ctr differentials.
You will not enjoy this satisfying feeling in a 4wd vehicle that does not have a mechanical LSD. This same feeling can be felt with the Sequoia when 4wd is engaged since its power has a dedicated distribution of around 40Fr/60Rr in 4wd with the ctr diff unlocked.
This same design philosphy equally applies to a rear mech LSD where transferring torque from one side to the other is the priority unlike a ctr diff which is addressing torque transfer from front to rear.
The new 08 RX330 with a viscous ctr LSD has this advantage of "guaranteed" power to both ends of the vehicle when in 4wd. This article describes the RX's new viscous ctr LSD as delivering a balanced 50/50 power distribution until slippage occurs.
#2188 of 2493 Re: RAV4 .vs. Subaru AWD [hdfatboy]
Apr 02, 2008 (2:12 pm)
I suspect that you would acknowledge that a simple center open diff'l will most adequately distribute torque 50/50 until slippage occurs. Just as long as both front and rear drivelines represent roughly equal resistance to the engine's applied turning force a simple OPEN diff'l will work perfectly well to distribute torque 50/50.
But no, my stated position is that I DO NOT believe ANY RX350 has a VC involved with the operation of the center open diff'l, including the 2008 model. And for that matter not even the new 2009 model.
Viscous clutch and coupling fluids can be formulated in an infinite number of ways. Some manufacturers even include a small amount of gas, a "gas" bubble, within the hermetically sealed fluid container, so as to delay the onset of the coupling coeffficient as the temperature of the fluid rises due to the "stirring" of the fluid by the clutch plates.
Suppose, for whatever reason, I drive my VC equipped '01 AWD RX300 in a very tight circle, as fast as is reasonable, continously for say, three revolutions. At what level might the coupling coefficient of the VC fluid rise to in that instance?
Frankly, I do not, cannot, believe that any Full-Time AWD system can be constructed using a center diff'l VC technique and have coupling coefficient responses on the order of anything less than multiples of seconds. And frankly, what is, where is the NEED..??
Think of the hazard that might result from driveline "binding" due to a quick and tight VC coupling coefficient as I enter a tight turn, even an accelerating tight turn, on a slightly slippery surface.