Steep Downhill w/Switchbacks in 4-Lo

[JTBurns]

I was just using 4lo on some tight trails this past weekend. Putting the shifter in manual and using 1st gave me great control downhill. Going uphill in some tight spaces, I used that off road cruise control feature a lot. It was really helpful, kept me between 1-4 mph as I navigated the path. It's a really cool feature

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[dcmdon]

Just put it in 4 Auto and you will be all set.

Oh you didn't order your Jeep with 4A. Ha. For the cost of a mid range light bar . . .

 

[j.o.y.ride]

I usually go back to 2wd for very tight turns and then back to 4lo 1st gear for creeping down steep stuff.

 

[j.o.y.ride]

Just put it in 4 Auto and you will be all set.

Oh you didn't order your Jeep with 4A. Ha. For the cost of a mid range light bar . . .

4 auto is high gear only, no 4 low auto. Using 4L for steep descents is to get the L, not the 4. 4A vs 4H is irrelevant wrt to this.

2L would be ideal.

 

[DankjeeP]

A question for all you experienced wheelers:

When descending steep trails with sharp switchbacks, do you use 4-Lo to stay off the brake?

If yes, when you reach a switchback do you leave it in 4-Lo?

If yes, is the "whomp whomp whomp" jerk of the steering wheel and front axle normal and ok, and something you accept?

(If no, do you put it in 4-Hi or 2-Hi?)

I ask because I do say yes to all three of these but making tight turns in 4-Lo gives me pause as I worry I'm damaging something. Any thoughts and advice appreciated!

Great question!

We did the Shafer/White Rim near Moab. I experimented with a few things, 4-lo seemed like a bit too much whine for the wife going down steep sections. She kept saying I'm going to damage something lol.

I just put it to manual mode and switched between 1st and second. On Hells Revenge I used the speed select button on the 25-30 degree slopes and it works great.
To your point though, we didn't experience any adverse steering conditions. Maybe the surface was loose enough.

 

[taliv]

you guys ever have it auto shift out of m1 to m2 or to N on a very steep hill when trying to engine brake and the revs get high?

 

[Terminus33]

Just put it in 4 Auto and you will be all set.

Oh you didn't order your Jeep with 4A. Ha. For the cost of a mid range light bar . . .

That doesn't help some of us that got our gladiator before you did...

 

[jsalbre]

Just put it in 4 Auto and you will be all set.

Oh you didn't order your Jeep with 4A. Ha. For the cost of a mid range light bar . . .

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.

 

[dcmdon]

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 chaining 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. 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.

Obviously it won't shift between 4H and 4L. But it would have allowed him to remain in 4WD of some kind and make the tight switchback turns without shifting in and out of 4WD.

 

[dcmdon]

That doesn't help some of us that got our gladiator before you did...

Oh shoot. I forgot it wasn't offered originally.

I'm still amazed. Nobody seems to get Selectrac. It seemed a no-brainer to me for $600.
And even locally in New England, none of the Wranglers or Gladiators that are (were) on dealer lots have SelecTrac.

 

[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.

Yeah, that is probably more likely why we didn't have the issue (my previous post) RCV's

 

[JoseQ_80]

It's a lot of rowing but if the switchback is tight enough I'll try to switch to 2wd beforehand then back to 4l and 1st gear or select speed control on. Repeat as needed it is good practice.

You can also leave it in 4L and learn how tight you can turn in 4L before it binds, but that varies by terrain.

So you need to make multiple point turns? No problem! Be patient and get it done.

 

[Aonarch]

The manual says not to exceed 25 mph in 4Lo. I try keeping that in mind.

Big thing, you need to shift to 4Lo before the obstacle not during. Sometimes you need to roll a mile per hour or two in order to engage it.

 

[Rockabillyroy]

The manual says not to exceed 25 mph in 4Lo. I try keeping that in mind.

Big thing, you need to shift to 4Lo before the obstacle not during. Sometimes you need to roll a mile per hour or two in order to engage it.

I shift into 4lo the same way I did with my JKU AT. Come to a stop, put it in neutral, shift to 4lo and then back into drive.
That being said, there have been times when I didn't put it in drive all the way and started to slide back while releasing the brakes. It's alway a WTF moment. hahaha... damn.

 

[JoseQ_80]

I shift into 4lo the same way I did with my JKU AT. Come to a stop, put it in neutral, shift to 4lo and then back into drive.
That being said, there have been times when I didn't put it in drive all the way and started to slide back while releasing the brakes. It's alway a WTF moment. hahaha... damn.

Same. If it won't engage let go of the brakes and it should pop into 4L.

The 25 mph limit is a feature, not a bug. It keeps you from going too fast and slaming into things and breaking something.

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