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Toyota 4WD systems explained

2400 messages,  Last post on Nov 22, 2009 at 10:30 AM

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#2363 of 2400 Re: So do all V6 4 runners have the 4wd full time in 4hi? [green] by wwest Jun 24, 2009 (8:27 pm)
Replying to: green (Jun 24, 2009 12:43 pm) Once you're underway the usefulness of the extra "drive" traction is mostly negated by momentum. You may also note that with more modern 4WD systems the ABS & VSC are disabled in 4WD mode. In some cases 4WD mode itself is disabled if you apply the brakes or if VSC activates. Traditional 4WD systems use a spline or dog clutch which cannot be quickly, reliably, disenaged, so these "features" are kept disabled.   Leaving a 4WD system engaged once underway is a lot like driving a FWD, or F/awd, patently UNSAFE. On an adverse condition roadbed, slippery roadbed, it is highly desireable to dedicate the front tire traction solely to directional control. With a locked center diff'l 50% of the engine drive torque, or ~70-80% of engine compression braking, is applied to the front wheels, leaving not much of the already low front traction coefficient for maintaining directional control.   IMMHO the best feature of ANY AWD system would be to remove all engine leading or lagging torque from the front tires as soon as the stability control system indicates a yawing condition, the vehicle is NOT following the "line" set by the stearing angle of the front wheels.   There is as yet, to my knowledge, NO FWD based AWD system that can accomplish that task.   The best "simulation" is to put your "traditional" 4WD system into RWD mode. Replies to this message: green (Jun 27, 2009 1:02 pm)
#2364 of 2400 Re: So do all V6 4 runners have the 4wd full time in 4hi? [wwest] by green Jun 27, 2009 (1:02 pm)
Replying to: wwest (Jun 24, 2009 8:27 pm) Thanks for the reply.
#2365 of 2400 Re: So do all V6 4 runners have the 4wd full time in 4hi? [wwest] by nedzel Jul 02, 2009 (6:51 am)
Replying to: wwest (Jun 21, 2009 8:02 am) wwest, so, in other words, you haven't driven a 4Runner in the snow. Go drive one and then get back to us. Replies to this message: wwest (Jul 03, 2009 9:19 am) nedzel (Jul 03, 2009 9:30 am) wwest (Jul 03, 2009 9:24 pm)
#2366 of 2400 Re: So do all V6 4 runners have the 4wd full time in 4hi? [nedzel] by wwest Jul 03, 2009 (9:19 am)
Replying to: nedzel (Jul 02, 2009 6:51 am) Assuming 4 good tires in both cases, what makes you think there is something to be learned driving a 4runner vs the years and miles, snow and ice miles included, spent driving the RWD/4WD(AWD)/4X4 Jeeps...??   Granted, the 4runner's AWD mode, 30/70 F/R torque distribution offers additional capability over the Jeeps, but then I get to throw in my years and miles, again with snow and ice miles, in my '94 AWD Ford Aerostar, 30/70 F/R unless slippage at the rear occurs in which case it goes to 50/50 for the next few minutes.   And if you happen to be bringing up the TC/VSC capabilities of the 4runner, NOTHING beats the PSM in my 996 C4 in that category. Replies to this message: nedzel (Jul 03, 2009 9:30 am) wwest (Jul 03, 2009 9:24 pm)
#2367 of 2400 Re: So do all V6 4 runners have the 4wd full time in 4hi? [wwest] by nedzel Jul 03, 2009 (9:30 am)
Replying to: wwest (Jul 03, 2009 9:19 am) WWest, in the winter I run snow tires on the 4Runner. I have four Nokian Hakkapeliitta snow tires, all with good tread.   I've driven the 4Runner in snow, with and without the center diff locked. You haven't. You can speculate and theorize about how you think it should handle in the snow, but you haven't driven it. I have. So please stop telling me about how it handles. I know how it handles. You don't. You haven't driven it.   I won't speculate about how your Jeeps, with different drivetrains, different suspensions, and different weight balances, handle in different conditions and different 4WD/AWD modes. You've driven them. I haven't.   Feel free to brag about your 996. I'm sure it is a very lovely car. But I fail to see how that is germane to how a 4Runner handles in the snow with the center diff locked. Replies to this message: wwest (Jul 03, 2009 9:24 pm)
#2368 of 2400 Re: So do all V6 4 runners have the 4wd full time in 4hi? [nedzel] by wwest Jul 03, 2009 (9:24 pm)
Replying to: nedzel (Jul 03, 2009 9:30 am) The 911 isn't germane to driving the 4runner with the diff'l locked, only unlocked with VSC and ABS enabled.   "...please stop telling me how it handles..."   We seem to have off-track pretty much solely on the issue of your 4runner being "tail-happy" with the center diff'l locked. Frankly I think anyone of actual knowledge or long experience will tell you that should NOT happen.   But again, just what is your definition of "tail-happy"...?   Mine would be: "f you step on the gas traveling straight down the road the engine torque applied to the rear will often result in the rear trying to lead the front. Pretty much SOP for RWD or R/awd but IMMHO NEVER in 4WD with the center diff'l locked.   Have you had a mechanic check and certify that your 4runner really does have the center diff'l LOCKED when the indication lights up...??
#2369 of 2400 Re: So do all V6 4 runners have the 4wd full time in 4hi? [nedzel] by wwest Jul 03, 2009 (9:55 pm)
Replying to: nedzel (Jun 18, 2009 12:01 pm) Maybe I see..   With the center diff'l locked ABS is disabled and since frictional braking is ALWAYS biased toward the front your 4runner will have a strong tendancy for the rear coming "about", especially when "braking" while traveling downhill. To some extend engine compression braking will have the same effect.   Your 4runner is not necessarily any more tail-happy with the diff'l locked than any other non-ABS equipped vehicle, RWD/FWD, etc, etc.   Yet another reason for NOT using the locked mode once underway at a decent speed.   One of the more common hazards, inadvertent engine "braking" of FWD and/or F/awd vehicles. Replies to this message: 2toyotas (Jul 04, 2009 9:22 am) wwest (Jul 04, 2009 1:57 pm) nedzel (Sep 22, 2009 6:35 am)
#2370 of 2400 Re: So do all V6 4 runners have the 4wd full time in 4hi? [wwest] by 2toyotas Jul 04, 2009 (9:22 am)
Replying to: wwest (Jul 03, 2009 9:55 pm) Nedzel, You will never win with Wwest. He still does not know that all toyota SUV,s, and trucks keep ABS and traction control active when in 4 locked mode. even in my tundra, which is part time 4wd, Traction control and ABS works when locked in 4WD. On new Tundras you can keep VSC active when in 4 locked. You are wasting your time because Wwest keeps arguing his point whether he is right or not. Just look at some of are previous posts. I gave up. Replies to this message: wwest (Jul 04, 2009 1:57 pm)
#2371 of 2400 Re: So do all V6 4 runners have the 4wd full time in 4hi? [2toyotas] by wwest Jul 04, 2009 (1:57 pm)
Replying to: 2toyotas (Jul 04, 2009 9:22 am) When the center differential is locked the front and rear drivelines MUST turn at equal rotation. Even if ABS were left enabled, which I do not believe, it could not be fully functional. The same goes for VSC. How could VSC apply differential braking, something it is often required to do, in the rear vs the front vs if the driveline has them locked together, braking the rear would automatically be "reflected" at the front.   The 2009 4runner owners manual indicates that VSC is disabled when the center diff'l is locked. Could find no reference to ABS one way or another.
#2372 of 2400 Re: Introduction [cliffy1] by usedcar3 Aug 05, 2009 (7:10 am)
Replying to: cliffy1 (May 16, 2001 2:55 pm) Beginning with the 2000 model year Land Cruiser, Toyota began using a new 4WD system called ActiveTrac. This same system was incorporated into all 2001 4Runners and the new 2001 Sequoias. The same basic system has also been used in the Mercedes M Class as well as post ‘99 Humvees.

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