Quote:
Originally Posted by cRiPpLe_rOoStEr
Makes me wonder to which extent a traditional 4WD truck would behave in the snow with the high-range 4WD engaged according to the load as the weight bias would be shifting.
I'd take with a grain of salt the viability of repurposing a transfer case into some sort of power-split device.
I'd rather not rely on a clutch-operated transfer case. Viscous coupling is more reliable. |
To clear up how the Astro and other GM transfer cases work from that era, it's what you could think of as a viscous clutch. There are several friction plates in the transfer case that can be squeezed together at various levels by what I do believe is a type of stepper motor.The plates are in the case in a special viscous lubricant along with the gearing and chain drive. When in 2WD or 4Lo/4Hi modes the clutch pack is either completely sqeezed or not. When in Auto mode (this is the only mode for the Astro) when rear wheel slip is detected the stepper motor sqeezes the viscous clutch pack just enough to virtually eliminate the wheel spin. That way the front axle isn't completely locked to the rear axle.
Anyhow, as far as what locked front to rear axle 4WD does on snow and ice goes: it can make understeer and oversteer even worse in some situations.
One time my brother in his GMC Sonoma needed to turn left. But there was a berm of snow in the middle of the street the snow plows had made. Where he was going lots of other cars had already worn down the berm so it was passable. However he thought it still would be a good idea to put it in 4WD and get a run at it. That made the truck understeer and he ended up stuck on the high part of the berm with all four wheels of the ground.
I've also noticed when decelerating that 4WD can cause oversteer as the weight comes up off the rear wheels and onto the front wheels while turning. I noticed the Dodge Durango I had would oversteer more at times with 4WD engaged. Basically it would understeer as I pulled out onto the highway, for an example. And so then I'd let off the accelerator and that would make it snap into an oversteer. It would react much the opposite in 2WD, oversteering when accelerating and then understeer when letting off of the accelerator. But it was the one vehicle I didn't get snow tires for, so that was a large part of it.
For the most part 4WD (or even AWD) is only helpful when driving slow. That being said, carrying around a snowplow on the front of a pickup with nearly no weight in the back makes pickups oversteer from wheel torque quiet terribly. So it becomes imperative to put it in 4WD even when not plowing snow.