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Old 02-15-2010, 09:13 AM #1
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Differentials - Auto LSD question
Hi. Can anyone explain to me why on my 2008 4runner, the "Auto LSD" (limited slip differential) on the rear axle only works when it is in 2WD? My car is all stock, with a center diff and lock. The only time the "Auto LSD" light comes on is when it is in 2WD and I press the Trac/VSC off button. I believe the Auto LSD is really a brake-based LSD (vs a viscous coupling diff), but why would it not work in 4WD too? Seems like it would be good to be able to lock the center diff and also have the ability to have the Auto LSD on the rear working at the same time.

TIA.

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Old 02-15-2010, 10:48 AM #2
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You're right that it's not really a true LSD diff, it uses brake and engine management.
Why Toyota limits it to 2WD I don't know. It may welll be possible to modify the wiring to allow it in 4WD, as can be done with many other of their systems.
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Old 02-16-2010, 12:00 PM #3
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The name Auto LSD is misleading. It is not fully automatic, it needs to be turned on and off, and that is done by pushing the VSC off button. It's actually a reasonably good system and technically better than a regular LSD because it can transfer 100% of the available power to the wheel with traction, opposed to only about 25% that a normal clutch/friction surface LSD can do.

I agree that it could be useful in 4wd, but it certainly makes 2wd more capable without the added power drain of 4wd. But a simple rear diff lock would have done that far better imo.
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Old 02-16-2010, 09:14 PM #4
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Thanks for the replies guys. I was talking to my dealer's service rep today so I asked why the Auto LSD light can only be switched on in 2WD and never for 4WD. He said it is because the Auto LSD is constantly on in 4WD. He almost had me believing it, but upon further discussion I got the feeling he just really didn't know what he was talking about.

Looking in the manual, it only makes mention of a LSD for 2WD and multi-mode 4WD models, and does not mention LSD at all for the full-time 4WD (Limited trim) which further convinces me it is designed to only work in 2WD. But I still don't know why. Maybe the 'braking' the system does somehow interferes with the 4WD, but I can't imagine how.
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Old 02-07-2011, 10:08 AM #5
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I have an 08 limited and am curious about this. When I start the truck and all the lights briefly come on I see an auto lsd light. I don't understand why this would even be there if it's only available in 2wd mode because my runner is fulltime 4wd and has no 2wd option.
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Old 02-14-2011, 11:29 AM #6
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Quote:
Originally Posted by stockrunner View Post
Hi. Can anyone explain to me why on my 2008 4runner, the "Auto LSD" (limited slip differential) on the rear axle only works when it is in 2WD? My car is all stock, with a center diff and lock. The only time the "Auto LSD" light comes on is when it is in 2WD and I press the Trac/VSC off button. I believe the Auto LSD is really a brake-based LSD (vs a viscous coupling diff), but why would it not work in 4WD too? Seems like it would be good to be able to lock the center diff and also have the ability to have the Auto LSD on the rear working at the same time.

TIA.

-------------------------------------------
2008 Urban Runner. V6 with multi-mode 4WD.
From my understanding the diff in a Toyota is a Torsen(sp?). Tosen uses gears. Viscous coupling uses friction, pads and fluid. Both systems can benefit from using break modulation. Brake modulation can happen automatically with the Toyota (traction control).

Not sure how it turns on and off in your vehicle.
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