Hello all, I'm new to the fourm and have been looking at the new 4-runner. I currently have a 08 Tacoma 2WD. My question is about the 4WD system in the base and trail editions. Part time 4WD can't be used for normal driving?
Correct. You can't use it on dry pavement. That is true of a Tacoma 4WD as well.
When you go around a corner, the path taken by your front differential is different than the path taken by your rear differential -- your rear wheels (and thus rear differential) cut closer to the curb than your front wheels. That is, the path taken by your rear differential is shorter than the path taken by the front differential, so the rear driveshaft must turn fewer turns than the front driveshaft.
In a part-time system, when you put it in 4WD the front and rear driveshafts turn at the same rate. So when you go around a corner, either the tires slip or you start loading up the drivetrain with added stress. When you are offroad or on snow, the tires simply slip. When you are on dry pavement, the tires can't slip as easily. This why you shouldn't drive a part-time 4WD system in 4WD on dry pavement.
In a full-time system like the Limited, there is a center differential (the Torsen) that allows the front and rear driveshafts to turn at different rates when unlocked, which is its normal mode. When you lock the Torsen center diff, the front and rear driveshafts turn at the same speed, making it behave just like a part-time system in 4WD.
I have read the limited version has a full time 4WD system. The Tacoma also has a part time system. If you don't travel off road and use the truck for day day driving in snowy conditions, is this a drawback?- or perhaps I don't fully understand. Thanks for you help.............
If the road is completely snow covered, then you are fine in 4WD with either a part-time or full-time system (whether locked or unlocked). The snow on the road allows the wheels of the part-time 4WD truck to slip. The Torsen is somewhat preferable because you don't always have a wheel slipping, as you do in a part-time system.
The problem is that in most places you aren't always on a snow-covered road. Where I live, in the winter the road sometimes goes from snow-covered, to partly covered, to wet, to dry, and back in the course of a mile. With a fulltime system, you just leave it in 4WD and you have the best possible traction at all times, with no concerns about stressing the drivetrain.
With part-time 4WD, you either shift in and out of 4WD as the road changes condition, or you risk stressing your drivetrain.
Most trucks have part-time 4WD, and yes they do get around in the winter. I prefer a full-time system, for all the reasons described above.