3.1.3) How does the Four Wheel Drive (4WD) system work?
Description
This article is from the Toyota RAV4 FAQ, by Ralph Becker with numerous contributions by others.
3.1.3) How does the Four Wheel Drive (4WD) system work?
Very well :) Actually, it depends on your choice of transmission, and
whether you have the Limited-Slip Differential (LSD) option. See the
Traction Adding Devices FAQ <http://www.a1.nl/phomepag/markerink/diffs.htm>
for more general information on these types of devices.
If you have a 2-Wheel-Drive RAV4, then it is powered by the front
wheels only.
If you have 4WD, a full-time system puts power down to all four wheels
at all times. Some refer to this as an "all-wheel drive" system, rather
than 4WD, but AWD usually refers to "reactive" systems that delay
transfer of power until after slip is detected. The RAV4 drive system
is most correctly called "Full-time 4 wheel drive." It is reported that
25% of the engine power is normally sent to each wheel.
- For automatic transmissions, there is a center coupling that
detects wheel slip and gradually locks the front and rear axles as
the slip increases. There are no driver controls for this feature.
- For manual transmissions, there is a center differential lock button
on the dashboard that manually locks the front and rear axles. When
engaging, an amber "C. Diff Lock" indicator lights on the dashboard.
When disengaging, there will be a beeping sound until the center
differential is fully disengaged; it may beep just once, or may
beep for as much as a full minute (seems to beep longer when cold).
Toyota recommends that it only be used only in difficult situations,
and that the center differential can be damaged if used improperly.
- For 4WD vehicles, there is an optional rear LSD available. In 1996
and 1997 model year, it was available only on standard transmission
models, but starting in 1998, the rear LSD is available in all 4WD models.
This device is called a "Torsen-type" LSD by Toyota, and is one of
the most sophisticated and effective types available. It automatically
detects wheel slip by either rear wheel and redirects the most power
to the wheel that is slipping the least. There are no driver controls
required for this device.
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