4wd nervous, jittery and jumpy, especially on turns

[DownBytheRiver]

Seriously? he didn't mention being offroad. No shit, you would use it in Moab, but even then you are going to get some lurching. I was talking about using 4wd on pavement. Obviously if you are on slickrock, you'd be in 4wd low no matter how good of traction it gives because you are likely not on even terrain. But even there it's going to lurch and be hard to turn, etc. Thats the way part time 4x4 systems work.

As for lockers, I use them when I need them. 90% of the time I don't need them. I learned to drive offroad with open diffs. Wheeled for 10 years before I had anything more than a single limited slip. I think part of the problem today is that people get Rubicons and then never learn how to wheel without lockers. Sad.

Same here. I'd like to add that I put it in 4wd for deep snow even before I slip. My philosophy is to use as little as I need, in terms of locking everything up, to give myself as much margin as possible to keep from getting stuck. And that includes recognizing when 4wd hi or lo is the right choice for the obvious places.

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[higbyz]

Even with the front axle and the rear axle having open differentials, the transfer case when put into 4L or 4H is locked front to back; both front and rear driveshafts will spin at the same speed. Therefore, power is being given equally front to back.

An example of turning left in 4wd: the front R wheel is turning faster than front L wheel, the back R wheel is turning faster than the back L wheel, as long as your lockers aren’t on there would be no slip there. However, in a tight turn, the front L wheel needs to turn faster than even the back R wheel causing the back R wheel to slip in a limited traction situation, or bind when there is a lot of traction like on pavement. This is where your lurching is coming from. This can be much improved by less aggressive steering input, or unpairing the front and rear drive shafts by going back to 2wd.

So ideally , you would really like to be going straight when you have it in 4wd ?

 

[InvictusManeo]

So ideally , you would really like to be going straight when you have it in 4wd ?

Well, when your off road and you have less traction, then your tires will slip more easily and that will put less stress on your drivetrain. The amount of stress put into your drivetrain is going to be related to how much grip your tires have. On pavement, where you have a lot of traction, this creates a lot of unnecessary stress on the drivetrain.

If your in a situation where you need to steer close to the limits, then you’re going to either have to deal with a little binding/slipping or change to 2wd and deal with less traction.

 

[Uhdinator]

1. For the love of Jeeps.......stop doing that on pavement. You're lucky you didn't pop a ball joint right out of the axle yoke.
2. When going off the pavement such as on to a logging road I stay in 2wd.
3. If I come to a muddy area where there's standing water/mud etc. I shift into 4H as I don't want wait till I'm in the middle of a mud hole at a stand still to shift into 4H. If it looks really bad/deep/slopply I may lock the rear axle only if you have lockers and use 4L if low speed is required due to very rough terrain.
4. When out of the mud turn off rear locker and go back in 2H if terrain allows.
5. When terrain gets to the point where its rough and slowing down to a crawl is required to avoid being pounded to death and beating your jeep to death........I go to 4L.
6. When crawling over rocks/stumps/off angle situations when traction is lost. If brake lock differential doesn't do its job, stop....lock the rear axle. Try again........if no go, stop, turn your front wheels as straight as possible and lock the front axle. Move ahead easy far enough to get over obstacle, stop unlock front and rear axle. Repeat as needed.
7. Only using lockers when needed will prolong the life of your drive train. There's no need to immediately lock everything just because you're off the pavement.
8. Brake Lock differential feature (always on in 2H/4H/4L) works very well when you understand how it works and use the correct technique. It requires gradually applying throttle (be patient and gentle) when a tire is spinning......the brake on that tire will gradually increase until it tricks the differential into thinking that tire has traction and the other tire will start to turn. If you are too aggressive with the throttle when the other tire grabs you could be launched.....
9. Those with lockers..........using them in rocky terrain when needed is better than relying on BLD as mentioned as you reduce the possibility of lunging abruptly into other objects.
10. Traction control is best for driving in 4H on packed snow and Ice (highway). It senses if one axle is spinning faster than the other as well as detecting you are moving slower than your axles are sensing/spinning. It reduces power/applies braking to correct the condition and keep you from spinning out into the ditch.
11. In sand or deep snow you want to keep your tires churning and keep momentum so turn off traction control so the engine does not reduce power or apply braking. In 4L traction control is automatically dis engaged but brake lock differential feature is always on.
12. Avoid turning hard as much as possible in 4H/4L. I do a multi point turn or use 2WD if traction allows. This will prolong the life of front axle u-joints and ball joints.
13. When the Rubicon was released in 2003 there were many videos and articles on front axle failures. The majority were due to too much skinny pedal when front axle is locked and not understanding some of the above points mentioned.

 

[baz]

It's from the '30s so it's a bit slow for our short attention spans these days

Slow!? Did you miss this part:

if the inner tires are able to move at different speeds

Maybe my mistake is in the above line (feel free to correct me if this is wrong). The rear wheels in 2H don't actually move at different speeds when there is traction, they receive equal power from the engine and move at the same speed, even during turns. What the open differential does is allow a wheel to spin faster only when it loses traction (which is when BLD kicks in?). But then doesn't this still cause some form of stress during turns due to the same principals discussed before of the outside wheel having to travel a longer distance than the inside wheel:

How is that accounted for? How can back wheels turn at the same speed without issue?

 

[DownBytheRiver]

Slow!? Did you miss this part:

Maybe my mistake is in the above line (feel free to correct me if this is wrong). The rear wheels in 2H don't actually move at different speeds when there is traction, they receive equal power from the engine and move at the same speed, even during turns. What the open differential does is allow a wheel to spin faster only when it loses traction (which is when BLD kicks in?). But then doesn't this still cause some form of stress during turns due to the same principals discussed before of the outside wheel having to travel a longer distance than the inside wheel:


How is that accounted for? How can back wheels turn at the same speed without issue?

No, both an open and anti-slip differential allows the attached wheels to turn at different speeds so the wheels don't slip on dry pavement.That's why it's called a differential.

 

[Rockit73]

Just want to thank the OP for the thread. I learned a lot about 4wd in my JLU Sport.

FWIW, I did go ahead and put mine in 4h several times a few minutes ago, on dry pavement, just to see how difficult it was, so I wouldn’t run into any surprises when I actually needed it.
Happy to say it easily went into 4h, with no bucking, clicks, pops, jitters or anything else, going in a straight line at 20 mph.
That’ll come in handy during the icy season here in DFW, and when I finally get it off-road.
Hadn’t really planned on doing any real off-roading when I bought it. All that has changed after checking out some YouTube videos (especially litebrite). Can’t wait to do some light off-roading asap.
Cheers, y’all!

 

[baz]

No, both an open and anti-slip differential allows the attached wheels to turn at different speeds so the wheels don't slip on dry pavement.That's why it's called a differential.

OK, I think I got it, mainly due to watching this video 30 times (specifically 1:10-1:36):

Here is an incredibly dry, boring, video that explains. It's only three minutes long but it's a rough one to get through.

Differentials operate side-to-side but have no coordination front-to-rear. So while the left and right wheels adjust correctly to a turn, the front wheels still have to complete larger turn radius than the rear wheels that is not accounted for:

So the back pushes forward at a higher speed but then meets resistance from the front causing the chirp and hop. Yeeeees?

 

[WillDo559]

Thread of the week! First he gets killed for driving 4lo on pavement then he tries to show that he goes off-road into a ditch then gets stuck in it lol, furthermore he records it and shows us all! I gotta appreciate your shamelessness, a lot of people did chime in and I'm sure that will help other people that didn't know as well. You sir might get a 4th subscriber today! I would love to see where you get stuck next, live and learn. Nothing but positive vibes

 

[jpclark]

I'm sure I have a problem. When I switch to 4H or 4L the drive becomes really bad. Going in a straight line the vehicle feels nervous, bumpy, jittery - but its survivable. Turning is a major issue that I'm going to the dealer for. On tight turns the jeep jolts back and forth thrashing and jumping. It's not usable, it's not safe. It's a 2019 Rubicon with 2500 kms on it.

Is this a known issue? Any idea what it could be? My dealer is low knowledge so I want to be able to point them in the right direction.

First... WELCOME to the 4x4 community. I'll refrain from stating what so many have already said, except to say that I was mischievously waiting to hear a "pop" of something breaking in your video. Seriously though... I'm going to offer some advise that I'm sure most here would 2nd... 1) Join a local Jeep/4x4 club, 2) Ask your local groups about who may be giving a "Wheeling 101" class. 3) Go on a beginner run with them, and 4) Do NOT engage your 4WD systems until you're off-road with that group and get some basic instruction. (The videos already shared here are great.)

 

[xtopherm]

Every 4x4 I've ever owned, going back 50 years, would do some hopping and grabbing in a tight turn, regardless of surface. It's a function of the turn radius.

Lemme take a stab at this...

When you turn a vehicle, the outside wheels obviously trace a longer arc than the inside wheels and therefore are turning faster - they are covering more distance in the same amount of time. But what is less intuitive is that the pair of rear wheels also cuts a shorter arc than the pair of front wheels - imagine driving on a beach - this phenomenon is why you get two tire tracks when you go strait, but four tire tracks when you turn. The rear wheels always "shortcut" a smaller arc as they follow the front wheels.

When you are in two wheel drive with an unlocked diff, it is no problem - the front wheels turn freely and the rear wheels can use the differential to turn at different speeds.

When you put it in 4WD, the transfer case rigidly locks the front axle to the rear axle so they must turn at exactly the same speed. The inside and outside tires can still turn at different speeds because the diffs are unlocked, but the rear axle hops since it is trying to trace a smaller arc and therefore turn more slowly than the front axle that is tracing a large arc.

The hopping, stuttering and slipping you feel from this effect is referred to as crabbing, and it is normal for the design used by Jeep. Crabbing is really hard on the drive train, but expected and part of the design. The only way to avoid it is to put a third differential in in the center of the vehicle. You see that in some off-roaders (e.g. some european ones) - in addition to front and rear lockers, they also have a center diff with a locker. In effect a Jeep has the equivalent of a center diff that is always locked - a transfer case that forces the front and rear axle to always turn at the same speed. Slow, wide turns on slippery surfaces make it barely noticeable. But the higher the speed, the tighter the turn or the grippier the surface, the more you notice it.

OK, so that is crabbing from the front and rear axles going at the same speed. When you add in locked differentials, you create a second source of crabbing from inside to outside in addition to your front to rear crabbing. Not only are the front and rear axles forced to turn at the same speed, but now the outside wheels are forced to turn at the same speed as the inside wheels. Now you've got four wheels that each need to turn at their own speed that are all being forced to turn at the same speed (in order of longest/fastest to shortest/slowest they are: front outer, rear outer, front inner, rear inner).

The result is a whole lot of drivetrain unhappiness and crabbing and a much more difficult time getting the vehicle to turn - the front wheels would much rather slip and push than actually turn, which is why you want to get at least your front locker off the minute you no longer need it (if not your rear locker too.)

This Jeep style system sounds crude compared to full time on-road systems with slip engineered in via things like viscous couplings, and admittedly it is, but its advantage is that, unlike viscous couplings and limited slip clutch packs, it does not have friction parts that are designed to wear out. It just has straight cut metal gears. It gives lots of control and it is tough as hell, and relatively cheap. Which is why it is used by all jeeps and virtually all full sized 4wd pickups, etc. This transfer case approach forces exactly 50% of the torque to each end of the vehicle when you are in 4wd. And when you are in a Jeep in 4wd with both diffs locked, you are guaranteed to get exactly 25% of the power to each wheel. That is why a Jeep with lockers can still make progress when only one single wheel has traction.

This system does crab and fuss in turns, but it is unbeatable for durability, cost, and getting unstuck in the worst situations.

Given how rugged these systems are, not to mention rudimentary quality assurance provisions on a new Jeep, it seems really unlikely that there is anything wrong with your jeep. It would not drive normally in 2wd if something was really wrong with either of the diffs and it would not drive normally in 4wd when going straight if there was something really wrong with your transfer case. More likely you are just on a surface that is grippier than you think and you are not familiar with how the crabbing, driveline lash and bucking feels on this vehicle. It can be quite pronounced if you don't have experience and a good touch with the inputs.

Hope that helps.

 

[YYCSahara]

I feel like SelecTrac 4x4 would have been a better choice, but that's not available with Rubicon I guess.

 

[xtopherm]

Thank you that explains it.

Edit: Actually, any idea how that works? Why would locking the rear and front drive shafts (which is what happens when switching to 4wd) still cause lurching during a turn if the inner tires are able to move at different speeds?

See my post towards the end of the thread for a full explanation...

 

[BroncoWranglerski]

@baz first time that happened to me I about had a shit fit. It’s normal, Its gonna happen, don’t worry about it. All 5 4X4’s I’ve had have done that.

 

[baz]

Lemme take a stab at this...

When you turn a vehicle, the outside wheels obviously trace a longer arc than the inside wheels and therefore are turning faster - they are covering more distance in the same amount of time. But what is less intuitive is that the pair of rear wheels also cuts a shorter arc than the pair of front wheels - imagine driving on a beach - this phenomenon is why you get two tire tracks when you go strait, but four tire tracks when you turn. The rear wheels always "shortcut" a smaller arc as they follow the front wheels.

When you are in two wheel drive with an unlocked diff, it is no problem - the front wheels turn freely and the rear wheels can use the differential to turn at different speeds.

When you put it in 4WD, the transfer case rigidly locks the front axle to the rear axle so they must turn at exactly the same speed. The inside and outside tires can still turn at different speeds because the diffs are unlocked, but the rear axle hops since it is trying to trace a smaller arc and therefore turn more slowly than the front axle that is tracing a large arc.

The hopping, stuttering and slipping you feel from this effect is referred to as crabbing, and it is normal for the design used by Jeep. Crabbing is really hard on the drive train, but expected and part of the design. The only way to avoid it is to put a third differential in in the center of the vehicle. You see that in some off-roaders (e.g. some european ones) - in addition to front and rear lockers, they also have a center diff with a locker. In effect a Jeep has the equivalent of a center diff that is always locked - a transfer case that forces the front and rear axle to always turn at the same speed. Slow, wide turns on slippery surfaces make it barely noticeable. But the higher the speed, the tighter the turn or the grippier the surface, the more you notice it.

OK, so that is crabbing from the front and rear axles going at the same speed. When you add in locked differentials, you create a second source of crabbing from inside to outside in addition to your front to rear crabbing. Not only are the front and rear axles forced to turn at the same speed, but now the outside wheels are forced to turn at the same speed as the inside wheels. Now you've got four wheels that each need to turn at their own speed that are all being forced to turn at the same speed (in order of longest/fastest to shortest/slowest they are: front outer, rear outer, front inner, rear inner).

The result is a whole lot of drivetrain unhappiness and crabbing and a much more difficult time getting the vehicle to turn - the front wheels would much rather slip and push than actually turn, which is why you want to get at least your front locker off the minute you no longer need it (if not your rear locker too.)

This Jeep style system sounds crude compared to full time on-road systems with slip engineered in via things like viscous couplings, and admittedly it is, but its advantage is that, unlike viscous couplings and limited slip clutch packs, it does not have friction parts that are designed to wear out. It just has straight cut metal gears. It gives lots of control and it is tough as hell, and relatively cheap. Which is why it is used by all jeeps and virtually all full sized 4wd pickups, etc. This transfer case approach forces exactly 50% of the torque to each end of the vehicle when you are in 4wd. And when you are in a Jeep in 4wd with both diffs locked, you are guaranteed to get exactly 25% of the power to each wheel. That is why a Jeep with lockers can still make progress when only one single wheel has traction.

This system does crab and fuss in turns, but it is unbeatable for durability, cost, and getting unstuck in the worst situations.

Given how rugged these systems are, not to mention rudimentary quality assurance provisions on a new Jeep, it seems really unlikely that there is anything wrong with your jeep. It would not drive normally in 2wd if something was really wrong with either of the diffs and it would not drive normally in 4wd when going straight if there was something really wrong with your transfer case. More likely you are just on a surface that is grippier than you think and you are not familiar with how the crabbing, driveline lash and bucking feels on this vehicle. It can be quite pronounced if you don't have experience and a good touch with the inputs.

Hope that helps.

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