murcod wrote:I know I haven't got an LSD from going off road in 2WD and getting stuck with one rear wheel in the air spinning uselessly. Anyone who's gone off road a bit should know from the amount of wheel spin they get from the rear (either you've got an open diff or your LSD is shagged if one rear wheel spins when lifted.)
Not necessarilly. With one wheel in the air the tailshaft drives the pinion, which turns the ring gear to drive the diff carrier. The two axle shafts are connected to the diff carrier by clutch packs (one clutch pack per axle.) A certain amount of torque is required to overcome the friction in the clutch packs, after which that axle will spin. If one wheel is in the air and the other on the ground, the clutch pack on the grounded axle will give in at relatively low torque, allowing the carrier to spin and the opposite wheel will spin with it (twice the speed actually, but lets not complicate matters too much.)
Thus, with one wheel off the ground the other wheel can only receive as much torque as is required to make the clutch packs spin - not normally enough to actually drive the car, particularly up hill.
This is where the handbrake becomes useful! By pulling on the handbrake a few notches you are adding resistance to the spinning wheel. There is a wedge type of mechanism in the diff which compresses the springs on the clutch packs as the drive torque increases, so not only do you add some "drive" resistance to the spinning wheel, you add extra grip to both clutch packs. This means more torque is required to get the clutches slipping - hopefully more torque than is required to get the car moving.
I've found my Paj spinning wheels and going nowhere, but three clicks on the handbrake allows it to drive out like there was never a problem. I think the key to it all is to be gentle on the accelerator. Too much throttle feeds in too much torque, overwhelming the clutch packs and allowing one wheel to spin. Once that wheel starts spinning the drive torque drops, releasing pressure on the clutch packs and you'll go nowhere.
If a wheel is spinning you're doing it wrong.
Scott
