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4WD and AWD systems explained

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Comments

  • paisanpaisan Member Posts: 21,181
    up to 18mph it will put some power to all wheels, then over 18mph only will it shift power after a split occurs.

    So it's not really AWD, it's more of an auto-engaging 4wd.

    -mike
  • pschreckpschreck Member Posts: 524
    I figured it would be you who answered. Thanks, I think I can trust you to have it correct.

    Paul
  • paisanpaisan Member Posts: 21,181
    It's a better system than some out there, cause you can lock it in 4wd under 18mph, and for most people it will do fine, but I'd rather see one that puts at least power to all the wheels all the time.

    -mike
  • pschreckpschreck Member Posts: 524
    Agreed.
  • wwestwwest Member Posts: 10,706
    Doesn't it default to FWD, and isn't there a driver control to lock it into 4WD?
  • paisanpaisan Member Posts: 21,181
    Yes it defaults to FWD, and you can lock it in 4wd, but only if you have the car ins the "1" and/or "2" position, and that turns off when the speedo hits 18mph.

    -mike
  • wmquanwmquan Member Posts: 1,817
    - FWD only during normal driving.

    - Up to 50% sent to rear tires during slippage; can be split differently between rear wheels.

    - Up to 50% sent to rear tires during acceleration.

    - Up to 50% sent to rear when the "lock" button is engaged AND the vehicle is under 18mph and in 1st, 2nd, or reverse gears. Percentage drops at speeds approaching 18mph.

    - Front wheels always split power evenly.
  • pschreckpschreck Member Posts: 524
    So the VTM-4 system is proactive up to 18mph and then becomes a reactive system requiring wheel slippage to engage the rear wheels?
  • paisanpaisan Member Posts: 21,181
    All he posted seem viable and is most likely correct except for a clarification on:

    - Front wheels always split power evenly.

    It's quite the contrary. The front axle/diff will send 100% of it's power to the wheel with the LEAST traction. This is the same as the front of all SUVs sold in the US (except for G-wagen, hummer and possibly one or 2 others costing well over $60K)

    Essentially the front diffy is an "open" diffy which routes power via the path of least resistance. For those FWD drivers out there, make a hard right turn from a stop(like a stopsign) and push the gas as hard as possible. What will happen is your right front tire will spinn when you punch it. For RWD drivers if you don't have a limited slip rear differential, your right rear would spin in the same situation. This is the same differential motion of the front axle on the VTM4 enabled vehicles.

    -mike
  • wwestwwest Member Posts: 10,706
    If you have ever come close too, or actually had, your knuckles busted or fingers broken due to driving a "part-time" AWD/4WD on a high traction surface while turning and accelerating slightly you likely understand why there are very few vehicles out there with ANY type of front LSD or front differential traction control.

    Too likely to yank the steering wheel right out of some soccer Mom's, or Dad's hands.
  • paisanpaisan Member Posts: 21,181
    Why would you drive a part-time 4wd vehicle on dry pavement? Are we soooooo dumb that we can't read an owner's manual to a $30K vehicle?

    :)

    But yes, that is probably the reason for no front LSD/Locker/traction control devices on the front wheels. Some vehicles with front LSDs...

    Sentra Spec V has a front LSD

    Hmm off the top of my head can't think of any others.

    -mike
  • wwestwwest Member Posts: 10,706
    Was your tongue in your cheek re reading owners manual?

    Today's dealers would go broke if everyone read the recommended scheduled maintenance routines.
  • paisanpaisan Member Posts: 21,181
    Seriously though. If someone doesn't bother to read the owner's manual for thier $30K truck it's not the manufacturer's fault!!! Just pointing out just how lazy we as a nation are.

    -mike
  • wwestwwest Member Posts: 10,706
    I don't really think so.

    Most of us are from the days when operating an automobile was simple and basically intuitive. 4WDs were left to Alaska and avid hunters. Nowadays suddenly everyone has one, all with different operating charactoristics and operating methods/modes.

    Twenty years ago, while so of us actually did, there was really no need to read the owners manual. Today I almost think the dealers should be required to hold classes for buyers before turning them loose on the rest of us.

    How many people do you know who learned to drive in RWD vehicles and now drive FWD vehicles and have no idea of the differing dynamics when arriving on the "edge" in low traction conditions?
  • paisanpaisan Member Posts: 21,181
    Have to agree, the laws are so lacking that it's ridiculous. We do need more drivers education. Personally I think that every 10 years we should be re-tested with road tests and all.

    -mike
  • wwestwwest Member Posts: 10,706
    I have been on a campaign with our state government officials to "force" (with a velvet glove) the insurance industry to develop driving simplators much like flight simulators.

    My primary point is that insurance companies are counter-modivated, the regulations allow them to make more money, in absolute dollars, the higher the accident rate is.

    If we turned that around and said we'll allow you a higher percentage of profits if you pitch in and help reduce the accident rates then I suspect we would have insurance companies jumping all over themselves to fund the developement of driving simulators.

    Most people only learn how to react, or not, in a dangerous situation as it occurs, and in many cases that's a tad too late.
  • pschreckpschreck Member Posts: 524
    What do you think of the X-Terra as a off road vehicle? Just wondering about you're opinion.
  • tidestertidester Member Posts: 10,059
    We're a bit off topic here but why would you want to force insurance companies to develop driving simulators? They don't know beans about technology.

    A competent hardware/software house would be the right place for such development and they would be motivated only if the market would reward them appropriately.

    Bottom line is that simulators would be of use only to one class of people - drivers! Use your velvet glove to get them into driver's ed classes.

    tidester
    Host
    SUVs; Aftermarket & Accessories
  • paisanpaisan Member Posts: 21,181
    It's a decent offroader by todays standards. Good notes: SWB, Frame, Solid rear Axle, 4-low Bad notes: Weak Engine (even the SC isn't outstanding), Expensive, undercarrige tire mount

    But If I were shopping for a "true" offroader, I'd definitely put it in the mix here's what I'd look at in that range:
    4-runner
    Rodeo
    Rodeo Sport
    Grand Vitara
    X-terra
    Liberty
    Wrangler

    -mike
  • pschreckpschreck Member Posts: 524
    That's pretty much my take on it. I do believe it's a nice looking truck (I know that's not that important).

    Is the line up you give in order of best to next best or is it just a list?

    Thanks
  • pschreckpschreck Member Posts: 524
    One more thing. Humor me. If you had $50,000 to spend on a NEW, STOCK, OFF ROAD (nothing used or modified) vehicle, just for your amusement, what would it be?
  • vin_weaselvin_weasel Member Posts: 237
    but my money would be on a '03 Disco or G-Wagen. Or a Rubicon and some spending money.
  • pschreckpschreck Member Posts: 524
    anybody can chime in on that question.
  • paisanpaisan Member Posts: 21,181
    Just a random list. I was shooting em off the top of my head.

    $50K new stock offroad... Hmmm... I'd like to say the G-wagen, except it's like 77K. I'd probably go with the Rubicon or Trooper or TLC. If I went with the Rubicon, the leftover would have to pay for the inevitible repair bills on it.

    Overall my favorite stock offroad vehicles of all time:

    FZJ80 (with front locker)
    Rubicon
    G-wagen
    Last gen Montero
    Trooper
    Samuri
    4-runner
    No particular order on that.

    -mike
  • cmack4cmack4 Member Posts: 302
    I know you said NEW and STOCK, but if creature comforts are of no concern to you... pick up a rebuilt post 9/73 build TLC FJ40 and install lockrite front and rear lockers as well as Marlen's Crawling gears in the transfer case. Upgrade the stock leaf springs and shocks, and you'll have one of the best (and hands down the toughest) pure offroad vehicles for probably less than $20K! With some of the money left over, you could always drop in a HO Chevy Small Block 350, and you'd have a decent highway cruiser as well!

    If I have to abide by your restrictions though, I'd probably stick with a new TLC. They ain't built like they used to be though!
  • paisanpaisan Member Posts: 21,181
    Since once you start doing heavy mods you can just buy anything and replace the whole suspension and driveline and essentially have a totally different vehicle.

    -mike
  • ateixeiraateixeira Member Posts: 72,587
    You should see Pipercub's BRAT, that thing is totally wild. It hardly resembles the stock vehicle, of course.

    Bone stock, I'd pick a Wrangler. Why waste the money when you're going to scratch the paint anyway? Plus spare and replacement parts are cheap and abundant, and off roading you will eventually break something.

    -juice
  • eagle63eagle63 Member Posts: 599
    actually I think the Xterra is pretty cheap for what you get. The engine isn't a rocket by any means, but it's not nearly as bad as the rumours you hear.
    good 4x4 list, but... grand vitara? hmmm....
  • pschreckpschreck Member Posts: 524
    Thanks for your thoughts.

    Anybody else out there want to get in on this. I'm hoping to get this topic going again. It appeared to be dead there for a while.

    Paisan, no mention of either version of the Hummer in your overall list. That's curious. Do you believe that they're overrated?
  • vin_weaselvin_weasel Member Posts: 237
    Too big for trails, bad gas mileage, cramped interior, and I prefer solid axles, lockers or not.
  • ateixeiraateixeira Member Posts: 72,587
    XTerra's V6 is torquey off the line, but gets wheezy fairly quickly. It's better around town than it is on the highway.

    Kind of the opposite of most small displacement VTEC engines. ;-)

    I 2nd the thought of the H2 being too wide for some trails. I've been on some Jeep trips where the roads were eroding and you could barely get by. It was so narrow you had to fold your mirrors. An H2 could not make that narrow pass.

    -juice
  • paisanpaisan Member Posts: 21,181
    H2 is a POS, just a suburban with a lift kit.

    The original Hummer and the H2 are over 50K IIRC. Also the original Hummer is pretty wide for trails.

    -mike
  • tidestertidester Member Posts: 10,059
    I am assuming you mean Plain Old Stupid.

    tidester
    Host
    SUVs; Aftermarket & Accessories
  • steverstever Guest Posts: 52,454
    Knowing Paisan, it stands for Pretty Overpriced SUV ;-)

    Steve
    Host
    SUVs, Vans and Aftermarket & Accessories Message Boards
  • tidestertidester Member Posts: 10,059
    That works!

    tidester
    Host
    SUVs; Aftermarket & Accessories
  • paisanpaisan Member Posts: 21,181
    Steve is right :) but it should be PDOPS! :) Pretty Darn Over Priced Suv :)

    -mike
  • pschreckpschreck Member Posts: 524
    They are huge. I always wondered how the Army was going to get them through the Black Forest.

    A buddy of mine had a CJ-3 back in the day. That thing went through the woods with ease. That was back when you could blaze your own trails and not feel guilty.
  • emptyempty Member Posts: 14
    H2 as Glorified Suburban is dead on. H1 at least has distinct 4WD machinery even if off-roaders find its capabilities lacking.

    Comments about H1's width also had me wondering how the military drives over "jeep" trails. Also reminds me of passages in _Blackhawk Down_ where the width is credited for righting HMMWV's as they drove through obstacles.
  • paisanpaisan Member Posts: 21,181
    The H1 was/is a great vehicle, especially for militarty or heavy duty use. Don't forget when the military rolls through, they don't have to be concerned about sapplings on the edges of the trail, they usually have bulldozers, and/or larger military trucks to escort them as well. The civilian H1 was kinda funny IMHO, seats were narrow, had that big center console for the driveline, etc. made it un-suitable for civilian use, most of them were for rich people looking for the tough guy image.

    Enter the H2. It gives the rich folk the tough image, but gives them creature comforts of a luxo car. The one owner I was able to talk to about his H2 looked at me like I was nutz when I invited him to come to the Pine Barrens with us for some light offroading. So I asked him if he bought it for the image, and he admitted "I didn't buy it for offroading, it's for the image" I said to hime "wow that's pretty sad that you have to buy it for the image"

    -mike
  • paisanpaisan Member Posts: 21,181
    Before that I was checking it's underpinnings out and realized I was looking at a suburban/avalanche frame and suspension with fake hummer rims (with the fake center air filler thing) and the body is just bolted onto that frame. Solid rear axle etc.

    -mike
  • ateixeiraateixeira Member Posts: 72,587
    Well, if you wanna turn heads, nothing matches the H2 right now. People gawk at them. So it's effective at providing the attention those folks want.

    -juice
  • lee83lee83 Member Posts: 3
    Hello to all Lexus People,
    I am new at this website. I'm considering to purchase a Lexus RX 300 but still being confused between 2 wheeldrive and 4 wheeldrive .I want to ask you as experts to help out: as I all know, we have two options for RX300: 2 wheeldrive or Fulltime 4 wheeldrive. Fulltime 4 wheeldrive is the same thing as AWD, has the meant ability to drive in the city all four wheels with no threat of driveline damage. When not off road, in normal driving, in downtown...it actually runs with 2WD mode, and only until slippering is sensed, it automatic switches to 4WD . Am I right at this point? For people almost do not go offroad, should they spend about 2 thousand dollars more to buy a 4WD to have both options? Beside for off road, is 4WD really worth over 2WD? I appreciate your time and thank for advices.
  • ateixeiraateixeira Member Posts: 72,587
    I'm not sure but I think both axles get at least some power all the time. Lexus uses a relatively simple viscous coupling in the center, kind of like Subarus with manual trannies. They also use traction control to manage both axles.

    It should be effective in eliminating torque steer vs. the FWD model, and give you more neutral handling, better traction on snow and rain, etc.

    The regular FWD models get traction control, too, so if you don't get too much snow, and didn't notice any torque steer with FWD, that might be a better choice for your wants.

    -juice
  • tblazer503tblazer503 Member Posts: 620
    is how long you usually keep your vehicles... If you are going to trade it in whtin 3-5 years it may be worth it to spend the extra 1,5 to 2,0 for the 4wd system... I believe that they usually maintain their resell value better... of course it depends on where you llive too...
  • pschreckpschreck Member Posts: 524
    Anybody know what kind of 4WD system is in the Navigator?
  • jack125jack125 Member Posts: 3
    Drew: I read your post #2 explaining the various systems, and plowed through another 200 posts trying to find how your explanations and definitions apply to Jeep's various systems and the practical effect. Finally gave up. I've also read Jeep info and talked to 3 Jeep service depts -- all of whom gave me different answers.
    Specifically, I'm trying to figure out which wheels are powered under what circumstances, in which systems. So far I think it goes like this: SELECT TRAK, which I have:
    - Part Time: both axles locked; 50-50 power to each; all 4 wheels powered regardless of spin;
    - 2 Wheel: 100% to one rear wheel.
    - Full Time: 48% power to front axle, one wheel only (right one?); 52% to rear, one wheel only (right one?), unless equipped with optional limited slip diff. "Varilok", which would switch power to the non-spinning rear wheel. So without Varilok, if both front and back powered wheels (right side) are spinning, the other wheels get no power. With rear Varilok (can't get front Varilok in Select Trak) option, you'd get 50% power to one rear wheel.
    QUADRTRAK II:
    - Part time: same
    - Full Time: 100% power to one rear wheel, until it slips, then 100% to front (one?) wheel, unless also have Varilok rear axle. If true, this would not seem to be as good as Select Trak's Full Time mode.
    QUADADRIVE:
    Part Time: same
    Full Time: 25% to each wheel, with power of spinning wheel transferring to non-spinning wheels. Although this seems to be the best for traction, one dealer told me they don't order QuadaDrive anymore since powering all 4 wheels all the time has produced "problems". ??
    Please correct any misconceptions I may have on how these systems work. If you've already answered this in some post, please refer me to the #. Also, I know QuadaDrive had some early problems -- but how about 01s and 02s? I'm trying to decide which system to get. Thanks, Jack
  • sebring95sebring95 Member Posts: 3,241
    lemme try:

    I believe selec-trac and quadra-trac II are identical in full-time operation and only differ in that the selec-trac gives you the option to operate in 2wd, full-time, or part-time. The quadra-trac is a full-time only system.

    Part-time:

    Power is split 50/50. Open-diffs on the front actually sends power to whichever tire has the LEAST traction just like any other open-diff system built. So technically, that 50% only goes to one wheel. If you have a vari-lok on the rear, then 50% would go to one front wheel, and the rear will split the power 25% to each rear wheel if slippage occurs. So you have the potential to power three wheels instead of two if you have the vari-lok option on the rear.

    Selec-trac and quadra-trac full-time modes:

    100% power to rear until slippage occurs and then it can transfer 50% to the front, of which one wheel will get the power. The front still has an "open" differential, just like the part-time system. This system is very similar to a traditional part-time system, except the transaxle doesn't send power to the front unless slippage occurs. Basically, it's an improvement over the part-time system only because you can run the system on dry pavement. With the vari-lock option on the rear, it does the same thing as on the part-time system

    Quadra-drive: This system has a vari-lok on the front and rear. Power will go 50/50 to one wheel on each axle until slippage occurs, then it will split 25/25 on each axle. As long as one tire has traction, you're set.

    The only question I don't know off the top of my head is if the Quadra-drive constantly delivers 50/50 power or if it delivers 100% to rear and then sends the power if slippage occurs. I believe it always runs 50/50 which is partly why I think people complain about this system. It's alot of extra drivetrain components running constantly and things can get noisey.

    The biggest complaint I've seen/heard is with the quadra-drive "whining". I've known a couple people with '99 quadra-drives and they did make some whining noises at times but they never had any problems with them. There was also some "clunk" or "bump" type complaints on the systems. One was really bad and there was a replacement axle to help. Others are lighter bumps and I've owned several 4X4's with automatic transmissions (two of which were Toyotas, one cherokee) that did the same thing from day one. Couldn't see where it hurt anything and none ever had anything beyond the occassional thump/bump or whine.

    I personally like the selec-trac system just because it gives you the option to run 2wd, full-time, or part-time. I find for typical bad weather (and I drive some very deep snow) along with off-roading, a part-time system with some sort of locking/limited slip rear axle will do the trick just fine. The conditions that demand a front locked axle just aren't that common unless you plan to heavily off-road the thing.

    The full-time mode on the selec and quadra-trac systems only adds the ability to have the 4x4 "standing by" on dry roads. Full-time is great for certain conditions, but I'd much rather run 2wd when it's dry. The advantages of the quadra-drive is not worth giving up the ability to run 2wd to ME, but someone that never leaves the pavement may not want to think about it. That makes the quadra-trak II a dud in my book because you can't put it in 2wd and it has no advantage over running selec-trac in the full-time mode. Plus you have the part-time option which has advantages in certain circumstances also.

    I'm not guaranteeing this data, but it's got to be closer than what many salesmen know about it. When I was shopping around back in July, most all limiteds/overlands were quadra-drive which meant I had to order or search the country for a limited with selec-trac.
  • hengheng Member Posts: 411
    He doesn't need to know anything technical but only that his service dept is constantly fixing the things (QuadraDrive) to the point that he knows his customers are having a bad experience with them. I'm looking (hoping) for objective evidence that the defect rate is improving on the newer JGCs.

    To Sebring95's points - I too rather be in RWD and select when to go into any other drive mode. But seeing how we are turning into a brainless society, the majority favor the AWD flavor.

    They then wonder why they are up to their rear axles in sand because the AWD was too slow to transfer power to the front, why they can't get up a gravel track because the traction control told the engine to power down or they expect AWD to save them when they hit a patch of white stuff going 70 mph on an interstate. (some examples I ran across in Town Hall) (sorry for the rant)
  • jack125jack125 Member Posts: 3
    Thanks for the info. So I'd conclude:
    - Even in Part-time, without varilok, if the one front and one rear powered wheels spin, you're stuck. Not what I expected.
    - Contrary to dealer info, Selectrak Full-time doesn't have any power to the front, unless the one powered back wheel slips.
    I currently have Select Trak and I also run in 2 wheel mode on dry pavement. However, I saw a post somewhere saying that's not as "safe" as running full time mode. -- presumably in an emergency swerve some front power might help -- but if there's no power to the front without rear slipage, that doesn't make sense either.
    Looking at the Jeep catalog, Select Trak is not available on a V-8 Limited. But Kelly Blue Book (kbb.com) shows it available. Does anyone know?
    Are there any objective surveys out there concerning problems with the newer QuadaDrive systems?
  • zaadzaad Member Posts: 9
    If not, isn't it dangerous?

    Just wondering if there is safety system involved to disengage the locking system to avoid having it locked for cornering & etc..

    zaad
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