Steep Downhill w/Switchbacks in 4-Lo

[DankjeeP]

4 Auto does not switch into and out of low range. However, having it on his JT would eliminate the feeling he's talking about, for reasons that will be clear in a moment.


OP:

The vibration you're feeling, commonly known as "crow-hop" isn't due to any binding so much as just the nature of the u-joints used in your front axle. 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. See the "Equation of Motion" section of this Wikipedia article for more info: https://en.wikipedia.org/wiki/Universal_joint.

Now, if you had the 4 Auto transfer case (MP3022) in your JT it would have been built with constant velocity (CV) joints in the front axles. CV joints don't suffer from he variation in input vs output speeds that u-joints do. We've known of this problem, and solution since the 1600s. The downside with CV joints is that if they aren't taken care of very well any contamination can destroy them in short order.

The reason the MP3022 is specced with CV joints is because it's theoretically more susceptible to damage from the vibration of u-joints.

There are some high-end CV joint axles available from RCV Performance for Jeeps and other 4WD vehicles.

Excellent post. Lots of good info anyone off roading even a little bit should know.

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