Read up on how part time 4WD works.. that's what our trucks are, part time.
Basically this means that the transfer-case does not contain a differential. This means the front and rear drive-shafts turn at the exact same rate.. which is either exactly the same rate as the input shaft from the trans, or slower, if you are in low-range. The key being that both drive-shafts are physically linked together, and turn at the same rate.
You've got differentials on both your front and rear axles. This means that the rate of rotation of either drive-axle will be proportional to the sum of the rates of both wheels. When you turn, the inside wheel forms a tighter arc than the outside.. this means the outside tire needs to turn faster than the inside wheel to cover the same wider arc. The differential let's it do this. But the sum of the two wheel-speeds still proportional to the input drive-shaft's speed.
So now you've got the front and rear axles linked together. That means they spin at the same rate. Then you ask one set of wheels to cover a different arc than the other set. Because the sum of the rates of each set must be equal, you end up w/ a problem. The result is you either have a tire that skids, or something in the drivetrain has to give. On slick surfaces getting a tire to skid is not an issue. But in high traction situations it is, so then something else in the system gives.. and that's usually something expensive!
Moral of the story: part-time 4WD is for slick surfaces ONLY.
Full-tme 4WD and AWD cars and trucks have a system that either uses a differential or a clutch mechanism where our transfer cases are. This lets the front and rear axles spin at different rates, and elminates this problem. Many fancy full-time systems (like high-end Jeep and Range Rovers) have a locking center diff. This gives them the best of both worlds, they have a diff for on-road, and can lock that center diff for off-road use.
2003 Ford Ranger FX4 Level II - Silver - Stick - fuelly
2009 VW Jetta SportWagon SEL - Grey - Stick - fuelly
2001 Suzuki Bandit 1200 - Red
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Last edited by NHBubba_Revisited; 11-14-2005 at 01:49 PM.