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- #136
So what makes the CV joint better than a U-Joint for 4A use?
Because of how u-joints are constructed the output shaft is continuously changing speeds versus the input shaft when the joint isn't straight, so each rotation your tires are speeding up and slowing down. How much of a change in speed there is is dictated by how far the wheels are turned. It's made worse by the fact that your two front wheels are rotating at different speeds from each other. When you use U-joints in a front axle it will “crow-hop” in turns while under power.
See the "Equation of Motion" section of this Wikipedia article for more info: https://en.wikipedia.org/wiki/Universal_joint.
CV (constant velocity) joints don't suffer from the variation in input vs output speeds that u-joints do, and thus don’t have crow-hop.
I guess it makes sense considering that 4A could be used even on dry pavement. But let's face it, 99% of the time you're only going to use 4A or 4H either one if it's snowing or really nasty weather otherwise outside. So I think they could have gotten away with the stronger and more durable U-joint design. Oh well, not a major crisis as ALL of the IFS systems use CV joints and they hold up pretty well considering..Ever tried to pull into a parking lot in 4H ?
Those joints bind like crazy even on snow.
They can't make sharp turns and having done driveshaft work for years, there are angles they are not supposed to make while under load.
4A may be engaged when making sharper turns. My truck almost slid into another vehicle as I tried to turn into a parking spot and the u-joints bound up. I had to back up and make another try - in 2.
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