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Comments
Is this normal as the dealer insists or is there a problem?
If the driveline isn't under "stress", driving or engine braking torque, then the spline type "dog" clutch will slide easily into or out of "gear".
The term AWD, All Wheel Drive, has been chosen to mean a drive system that somehow has some elasticity in the driveline between the front drive and the rear drive.
The most viable, most functional on adverse roadbed surfaces, of these (4runner, Honda/Acura SH-AWD) are rear torque biased and with the ability to remove ALL drive torque, leading or lagging (engine compression braking) from the front wheels when or even directional control is threatened.
Insofar as I can tell the entire Toyota and Lexus FWD based AWD fleet are referred to as AWD for marketing purposes only. Very little real, or no, AWD functionality whatsoever.
http://classes.engr.arizona.edu/engr498a/2006/fsaediff/resources/techart3.pdf
My only remaining question is if it would be better for Toyota to use LSDs rather than open diffs front and rear.
You won't have any trouble selling your vehicle should it not meet your expectations. Your post makes it appear though you needed a vehicle with a longer bed to begin with so your Harley wasn't riding on the tailgate. My neighbor has the same vehicle as yours in the DC configuration and has had -0- issues. Another neighbor got a DC 4X4 shortly thereafter, and has no complaints either. Both are 2007 models.
tidester, host
SUVs and Smart Shopper
The Highlander is F/AWD, and that for marketing purposes only.
Note that there is a MYRIAD of F/AWD implementation methods out there in the marketplace, all with varying degrees of multi-wheel drive capability. The Acura/Honda SH-AWD system likely being the best of them, but in my opinion still inadequate for the conditions of travel you encounter.
The Highlander uses three, front/center/rear, fully open differentials and would therefore be a 1WD vehicle were it not for the electronic braking capability provided by the TC, Traction Control, system.
Many owners are already complaining that the TC system is totally inadequate for getting the vehicle unstuck, or even up and going on a slippery surface initially as long as TC is active.
As a result some Toyota and Lexus F/AWD vehicles now have a TC disable function so the driver can use at least some level of wheelspin to get unstuck or rock back and forth to get unstuck. But one must keep in mind that with TC disabled you are back to 1WD.
Toyota is also introducing a new form of TC called A-LSD, so far only installed on RWD or R/AWD vehicles, and apparently only activated if primary TC is disabled. A-LSD stands for Automatic Limited Slip Differential.
It has always made sense to have LSD for a rear differential but somewhat hazardous, absent some driver familiarization training, for implementing at the front differential.
IMMHO the vehicle you're really looking for is the Toyota 4runner. The 4runner has RWD mode, AWD mode, and most importantly for those logging roads, TRUE 4WD/4X4 mode, capability.
But the key question to ask those salespersons is if the front driveline can be locked, SOLIDLY LOCKED, to the rear driveline for travel on those several miles of logging roads in the wintertime, or MUDDY spring. And I would be sure, CERTAIN sure, that whatever vehicle you purchase also has some form of rear LSD.
As for the Highlander, I thought it had a viscous fluid unit between front and rear which automatically stiffens if there is a difference in speed. I would call this a form of limited slip and not 'open.'
Lexus.com still indicates the RX350 has a VC but the documentation indicates that it does not. I'm in an ongoing argument with Lexus customer service about this at this very moment.
Because the LSD is not as good as a locking differential when there is zero traction such as when one tire is in the air.
But if the car can detect that tire slipping and use the brake just on that wheel, it can force 100% of the torque to other wheels. This comes close to the performance of a fully locked differential.
A LSD does not redirect all the torque, just some percentage of it.
My 1997 Hummer H1 had all limited slip differentials and the instruction manual said that if one wheel was in the air, you could force it to not spin by applying the brakes. The Torsen diff would then act as a torque-multiplier and make the other tires overpower the brakes and move. In 1999 they improved this by having a computer just only apply brakes to the wheels actually slipping instead of all of them. They still kept the LSDs. As far as I can tell, it is the ultimate full time system and probably just as good as 3 locking diffs without having to turn them off on pavement.
So we bought another new Jeep Grand Cherokee with true 4WD ie lo range & 6500 class4 towing. I'd thought about the new 08 Liberty but the JGC handled night/day better. I also liked the Commander but the 3rd seat was a joke. Yes the Jeep only gets 15 city/20 highway mpg ($300/year for gas than a Highlander or Rav6) but it has a lifetime drivetrain warranty and our 01 was very reliable .
No debate on it's 4WD system either if you need true 4WD QuadratracII does it.
See the Edmunds Gr Cherokee forum for info http://townhall-talk.edmunds.com/WebX/.eea4ead/1030 or http://www.wkjeeps.com/wk_4x4.htm
Does Toyota actually brake spinning wheels to improve traction from the remaining wheels, or do they cut engine power to keep the spinning wheel from spinning?
But as I am considering a RAV4 "AWD" .vs. Subaru Outback AWD .vs. Subaru Forester "AWD" (that system's more reactive than the Outbacks'), some comments would be welcomed.
The car brakes just the spinning wheel. It can also cut some engine power as needed, but the braking is what forces the torque to move through the diff to another wheel.
I think my 1999 Mercedes SLK only cut engine power but I am not sure.
So if a front wheel spins/slips then both front brakes are applied and the engine is simultaneous dethrottled to prevent subsequent brake/rotor overheating and warping.
Then there is the BMW X3/5 with REAL AWD, R/AWD.
Bob
Is a game of volume...like insurance. That's how they make money. If it makes you feel better having the added protection then by all means purchase the warranty. You probably have better than a 50% chance you'll use some or all of it and recoup your cost anyways.
Any way to know whether it is in 4 Wheel drive, other than depending on that "4 Wheel light" indicator on the dash?
I plan to take it back to Dealer, but just wanted to get some insight from unbiased folks.
Thanks, Zingaro_Mom!
I think the Toyota warranty is actually a pretty good deal if you have any intention of keeping the vehicle for 100,000miles. I think it is almost a given that something is going to break on the 08 Sequoia between the 3rd year and the 7th year of ownership or between 36,000miles and 100,000miles. Even more likely given its a new model with a new engine, new rear suspension design, new electric seat design, new 6sp transmission design, new 4wd system design, etc.
I am equally sure that whatever breaks during that period is likely to cost significantly more than $1000. Combined with the fact that unlimited towing and a rental car is included in the Platinum warranty, it seems a pretty reasonable bet to purchase a 7yr/100,000mile/$0 deductible from Toyota, particularly if you can purchase it for under $1000.
This newer system does not exist on most of their older models (I think it was on the older 4Runner models). I believe there is still a significant disadvantage that remains in Toyota's A-LSD system.... it does not function above 35mph. This limitation means that for all of these Toyota vehicles with the new 4wd system, when operating above 35 mph, they really only have traction to one wheel on the front end and one on the rear distributed through the mechanical center differential (the rear differential is still open on the new 4wd system). This can make a difference on wet highway ramps and other higher speed situations (above 35mph) where traction at all 4 corners is desirable.
The power is distributed through the new Torsen Center Differential with a range of 30/70 upto 50/50 when operating in full-time 4wd. The other downside to Toyota's A-LSD is that because it is based on using the brakes to distribute torque when there's slippage (below 35mph), it can have a tendency to wear out brake pads sooner than a system that doesn't use brakes to distribute torque (ie, mechanical LSD or lockable LSD). I don't know how much additional wear there is but it must be something vs a non-brake method for distributing torque during slippage.
Toyota's new full-time 4wd design is better (for on-road use) than the old system which had 3 open differentials, but its still not as good as AWD systems used by Audi, Subaru, Dodge, GMC and Cadillac that use a LSD for the center and the rear of their FT 4wd drivetrains.
In normal, non-adverse roadbed, conditions none of these engine/transaxle combinations will produce enough torque to induce wheelspin/slip above 35MPH, so above that speed the number of driven wheels is generally not of matter.
If you have reached 35 MPH and the roadbed is slippery enough that the engine will induce wheelspin/slip and you force it to do so you simply do not belong on the same roads as others with more common sense.
With A-LSD I suspect the manufacturers have an expectation that over time the drivers will adapt to "learned" road conditions and thereby do their own "feathering" of the throttle to avoid wheelspin/slip. That should avoid most uses of the brakes to implement the A-LSD system.
The TC, Traction Control, system in my '92 LS400 works very well as a warning, heads up indication, of roadbed conditions for which I may have been unaware, was unaware, but once I get that warning I typically turn it off and drive a bit more cautiously, as conditions warrant.
If you have reached 35 MPH and the roadbed is slippery enough that the engine will induce wheelspin/slip and you force it to do so you simply do not belong on the same roads as others with more common sense."
Your view may be reasonable however there have been enough circumstances where I was on a sloping ramp in snowy or wet conditions that I was glad I had a true AWD/FT 4wd system that incorporated a mechanical LSD in both the center and rear differentials. Obviously Toyota engineers felt it offered enough of a benefit to warrant their change over to a mechanical center differential on their newest high-end 4wd models. I just wish they had done the same on the rear differential for the same reason they elected to incorporate it into the center differential.
I would think MB, Audi, Subaru, GMC, Dodge, Cadillac, BMW, Chevy, Land Rover, Porsche designed their AWD/FT 4WD systems with a mechanical LSD in both the center and rear of their drivetrains for a good reason. IMHO that reason being that it delivers a more sure-footed driving experience without the speed limitations and brake wearing downsides of the Toyota electronic approach.
Here's an article that might be of interest on the differences between AWD & 4WD.
http://www.omninerd.com/blogs/4WD_vs_AWD_and_the_Fallacy_of_Snow_Traction
2008 Audi S4 Quattro http://consumerguideauto.howstuffworks.com/2008-audi-a4-5.htm
"4.2-liter 340-horsepower V8 engine, 6-speed manual or 6-speed automatic transmission w/manual-shift capability, all-wheel drive, front and rear limited-slip differentials".
2008 Chevy Tahoe LTZ 4WD http://autos.yahoo.com/chevrolet_tahoe_ltz_4wd-review_article/?source=nctd
"a limited-slip rear differential"
2008 Subaru Baja http://www.allautoreviews.com/auto_reviews/subaru/suburu-baja.htm
"5-speed manual transmission full time 4WD viscous center differential center locking differential rear limited slip differential"
2008 GMC Denali http://www.motortrend.com/cars/2008/gmc/yukon/denali_sport_utility/553/specifica- - - tions/
"Rear limited slip differential "
2008 Cadillac Escalade Same as Denali
2008 Dodge Dakota 4WD http://www.dessources.com/en/newcars/perfectcar/index.spy?carid=1081500811&ORIGI- - - N=0&DEALERCODE=514DESSOURCESDODGE&lng=en
"Limited-slip rear differential"
2008 Mitsubishi Lancer Ralliart http://www.autoblog.com/2008/01/13/detroit-2008-2009-mitsubishi-lancer-ralliart-- - - were-sold/ "4wd Lancer Ralliart is also equipped with front helical limited slip differential and a rear differential mechanical limited slip differential"
2008 BMW All M series and Z series vehicles have mechanical LSD in the rear. It is unclear what type of differential is used in the rear of the X series. They do use a mechanical LSD for the center but I was unable to find info on the rear. http://www.motortrend.com/cars/2008/bmw/x5/specifications/
2008 Land Rover LR3 http://www.automobilemag.com/am/99/2008/land_rover/lr3/hse_sport_utility/877/pac- - - kages_options.html
"Heavy Duty Package - $625 Rear limited slip differential"
2008 Porsche Cayenne http://www.allautoreviews.com/auto_reviews/porsche/porshe-cayenne.htm
"6-speed shiftable automatic transmission descent control four wheel drive full time 4WD hi-lo gear selection front, center and rear locking differential"
2008 MB 4matic http://www.edmunds.com/mercedesbenz/sclass/2008/review.html
This is a new system for 2008 and appears to have a mechanical LSD for the center and electronically locking front and rear diffs. The S63 does have a rear LSD. "a performance package for the S63 provides a limited-slip rear differential"
Uisng a viscous clutch, a spring pre-load clutch set, or....
the brakes...??