Monday, Jan 04, 2016 at 22:07
Why wouldn't you put one in the rear?
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They can cause some degree of rear wheel steering in some situations. This can be just about eliminated if the driver fully understands the operation of the locker but I doubt if very many do. There is an endless amount of incorrect information about them on the net. I am not aware of any car manufacturer who has fitted an auto locker to the rear. I think far too many drivers would get into trouble with it.
One simple example would be turning a 90 degree corner at slow speed in a city. We have all seen cars slow down then turn quickly and accelerate away rapidly in first or second gear. The car might lean a little and the inside wheel will loose traction and spin for a second or two. That will lock the diff instantly and could cause a sudden and unexpected change of direction of the car.
A similar thing can happen at higher speeds if a powerful car is accelerated quickly to change lanes or overtake. Wet roads can make the loss of traction of one wheel much easier.
The dirt roads that you mentioned can also be a problem. I have a friend with lokkas in both ends of his car and he said he has occasionally felt the car wanting to go straight ahead while turning on smooth unsealed surfaces. This would be because the wheel on the outside of the corner has not got sufficient traction to roll ahead of the other one. He does understand their operation so he aware that it can happen and it has never worried him.
The basic operation of these things is the wheel with the shortest distance to travel will always be driven by engine applied torque while the one with the longest distance will be able to roll ahead driven by road applied torque. If the driven wheel looses traction, the diff will lock and the car will keep going providing the other wheel has traction.
In practice both wheels vary rarely turn at exactly the same speed due to constant variations in road surface. The variations are major in the bush but still exist on sealed roads. Tyre diameter also varies ever so slightly due to different amounts of wear. There may also be minor differences in diameter between same size tyres from different manufacturers. The result is you can drive an auto diff locked car around cities or the bush all day with few if any problems but you can't do that with a manually locked diff.
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