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Toyota 4WD systems explained

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  • 2nupe2nupe Posts: 1
    I recently purchased a 1998 Toyota Landcruiser. I know very little about locking differentials, etc. I live in Maryland where we don't get much snow. Under what circumstances (a couple of inches of snow, ice, wet pavement) should I change the setting from 4H to 4L and when should I lock the differential (I also have the rear differential option)? Also, how do you change settings (on the fly or at a stop) and how do you lock the differential (on the fly or at a stop)?

    I have three instruments, the 4H N 4L shifter, the locking differential knob on the left of the steering wheel, and the differential button in the main controls near the air conditioning buttons. Which controls which?
  • cliffy1cliffy1 Posts: 3,581
    Unless you are going off road, there are never too many situations in MD that would require you to either lock the differentials (either center or rear) or shift into the low range. To engage low, you first need to stop and place the transmission in neutral. Use this only if you are pulling somebody else out of a ditch or are in a ditch yourself.

    As for the center and rear locker, again unless you are doing some fairly serious off roading, don't mess with them. If you are, send me an e-mail at sclifford@kjtoyota.com and I'll go into it further.
  • On my new highlander do?
  • tonychrystonychrys Posts: 1,310
    The Snow Button will force the auto-transmission to start in 2nd gear after you come to stop (like at a traffic light) rather than 1st. The reason is that by starting in 2nd gear you are applying less torque to the wheels and less likely to spin them on a snowy surface.
  • cageymcageym Posts: 6
    I live in the suburban Chicago area where, frankly, my need for an all wheel drive vehicle seems not too great to me. But as I talk with friends about shopping for a new car (about 100% sure it will be a HL), everyone tells me that I am crazy not to get AWD. They maintain the AWD will handle better, etc. I counter with reservations about fuel consumption and additional expense, and they scoff at me. We all seem to agree about the value of the skid control, at least in theory. Anyway, I'd appreciate some discussion of the pros and cons of 2WD vs AWD in these instances. I mean, I will not be off-roading in this car and the snow has never been much of a problem for me in my little FWD compact....

    Thanks for your indulgence!
  • drew_drew_ Posts: 3,382
    You may want to read the messages in the 4WD and AWD systems explained discussion topic too. You're already spending a fair amount for the Highlander. Why not spend a bit more to get the safety and security of AWD? Getting an SUV without 4WD or AWD, in my humble opinion, is like buying a minivan with only 5 seats.


    Here's something that may help you to decide.

    http://www.4x4abc.com/4WD101/tractionturn2.html

    http://www.4x4abc.com/4WD101/need.html


    Drew
    Host
    Vans, SUVs, and Aftermarket & Accessories message boards
  • chadhburkechadhburke Posts: 27
    Thanks for the previous posts on various terminology and an explanation of the AWD system on the Highlander. I've got a HL with the skid control option. If I understand it right, the HL has open differentials on the front and rear, in which case it is possible to have both left or both right wheels spinning under the right (or wrong) circumstances. Now, it sounds like at that point the VSC feature would kick in by applying the brakes to the spinning wheels. At that point, power would be diverted to the other wheels.

    Assuming what I've said is right, then it seems that it would take some work to get the HL stuck. I know very little about driving in "off-road" conditions, and would like to know if I am likely to get stuck in say mud of different depths, snow, etc. Also, is it ok to drive my HL in off road conditions so long as I don't encounter serious ground clearance obstacles? (i.e. are the suspension and other components "tough" enough to handle rough but not abusive terrain?)

    Thanks
  • cliffy1cliffy1 Posts: 3,581
    By jove, I think you've got it! The real limiting factor in off roading for you is ground clearance and the fact that the HL is a unibody. The unibody means that the body and frame are a single unit and you can flex it by going too serious off road. The 4Runner has a frame to take up this stress but rides more harshly on road.
  • kmhkmh Posts: 143
    I own a '99 RX300 AWD which has a rear limited slip differential. I haven't found a clear answer as to what the power ratio or split would be should there be on this model. Is it 50/50? 70/30?

    My '99 is coming up on 60,000 miles - what sort of maintenance should I look into for the AWD or LSD?
  • cliffy1cliffy1 Posts: 3,581
    Yours is a 50-50 power split. Your second question is a bit confusing though. You ask whether you need an AWD or LSD. The LSD is only something you can get on the AWD model. Were it me, I'd skip the LSD and get the VSC instead, which I think is standard on the RX anyway.
  • kmhkmh Posts: 143
    Sorry if I mislead you on the second question.

    What I was wondering was what sort of maintenance considerations should I take into account for my AWD with the LSD? Is there any special needs for maintenance at 60,000 miles because of the AWD and LSD?

    Many thanks!
  • cliffy1cliffy1 Posts: 3,581
    As you noted, the rear LSD does need maintenance. The clutches can and do wear out and will eventually need to be replaced. When they do wear out, you will not notice anything drastic. They will just stop transferring power to the side with the most traction. It literally reverts to an open differential.
  • cliffy 1,

    Thanks again for all the informative postings. My question, which by implication you may have already answered, is whether the sequoia's transmission must be in "L" to engage 4wd low? The reason I ask is that you imply that 4wd low is essentially designed only to extricate the vehicle from a bad situation. My experience with 4wd was with a 76 LC, the ultimate in conventional 4wd as you say, in Colorado, and I rarely ventured off road without 4wd low engaged simply for the ability to handle steep grades. I rarely got stuck, but I was always going uphill. I love the idea of the 3 open miff's saving wear and tear with the tracs computer easing any potential bog downs, but can it work in 4wd low. (trans in "D" ?) Thanks for any info.
  • cliffy1cliffy1 Posts: 3,581
    The low gear range operates in all gears. If you shift the transmission into "L", the center differential is also locked and the TRACS system is disengaged. This means that as long as you don't have the transmission in "L", you have the low gear range plus the TRACS and open differentials working for you.

    Great user name by the way.
  • llofgrenllofgren Posts: 129
    Cliffy1,
    Thanks for your excellent explanations on these systems. You mentioned that the HL center diff maintains (with the transfer case) a 50-50 split between front and rear. If there is Front slip then the viscous coupling thickens and routes more power to the rear.
    Two questions: 1) Can the opposite happen? That is, if there is rear wheel slippage, can power be transfered to the front so that the front wheels are getting more than 50%?
    2)Does the system work when the transmission is placed in Reverse?
    Thanks!
  • cliffy1cliffy1 Posts: 3,581
    The answer to number 1 is yes.

    I'm not positive on the answer to number 2, but I don't see why it wouldn't. The viscous coupling center differential is pretty simple and if one drive shaft begins to spin more than the other, power is transferred. I don't see why direction would impact that.
  • kmhkmh Posts: 143
    Say I'm going along and my front wheels begin to slip in my RX 300. Power is transmitted to the rear tires, correct?

    Everything is going along with power to the front and rear wheels until one of the rear wheels begins to slip... Does the power then move forward to the front wheels?

    At what point does the transfer stop? When there's no longer any wheel slippage?

    I apologize if I sound completely ignorant on this, but I am in a way and merely want to understand what my RX is doing in conditions when the transfer occurs. Thanks!
  • cliffy1cliffy1 Posts: 3,581
    You've got it! The power equalized when traction is equalized.
  • brillmtbbrillmtb Posts: 543
    cliffy,

    Good job on helping folks out on the Toyota systems. I found that the dealers couldnt even explain it and they go to the training.

    I would disagree on something you said in an earlier post. It is not the unibody that would limit the HL. It is suspension design, one aspect of which is the ground clearence you mention.

    Then again, I hope nobody is considering much off roading in the HL anyway. So my point is, the highlander should do fine for its intended purpose just as the whole line of Toyota products seem to do.

    The trick is to figure out what you want to do then find the SUV to match it.
  • Cliffy,
    My wife was driving my '99 SR-5 through Kentucky on I-75 while I slept in the back. It rained hard and fast and she hit a puddle and hydroplaned at about 55 mph. I awoke and saw her turning into the skid but knew she wasn't going to be able to correct it. We ended up rolling over 3 times, landing back on the wheels. Luckily we walked away from it. She doesn't drive my truck very often and isn't familiar with it's handling. Could this have been prevented if this vehicle was equipped with VSC and in 4WD?
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