Rubidonn

That's quite interesting 'E'... I guess I thought when you were in 4 LO, that all the electronic braking $hit was turned off and wouldn't do as you mentioned above (computer trying to apply brakes and stuff). You make some good points, however in a senes I think you just repeated part of what I said... and that was both front tires are wanting to spin at the same speed... since you're turning, one tire needs to travel further and one needs to travel less... therefore you will see the jerking front steering wheel occur. It is the same is if you were locked up... except when you're locked up, it's even more apparent - big time.

Lucas718

Now I'm confused. So if you're not offroad, when would you ever use 4wd? Just in the snow? In my Liberty I sometimes switch to 4wd hi when it's raining and I'm at a stoplight and I know the wheels are gonna spin. Should I not do that? I always switch it back to 2wd once I start moving.

Ge99ne

well if the tires are prone to slipping its okay to put it in 4 hi. Generally speaking wet raods don't really warrant 4WD. AWD is more suited to this type of traction assistance.

And if I had to take sides inthe left wheel right wheel vs. front wheel back wheel debate, then I choose Jake. The brakelock rant took things a little away from the root question.

Since wrangler Chuck didn't make mention of locking the axles, I'd go with jake's explanation. I completely agree with the lockers having a similar effect.

This keeps getting muddied, but 4 lo does not turn off the brakes attempts to simulate a limited slip.

moun10eer

KJ (Liberty) has 4HI / FULL-TIME which works like AWD and can be used even on the dry pavement (front 45% / rear 55% power - unlocked).

I wouldn't use 4HI / PART-TIME for rain (front 50% / rear 50% - locked). ESP is there for that. That said, if I'm on the very steep hill (there are many here in Seattle) and I know it's going to spin/slide because of snow or heavy rain, I probably use it just to get going... as long as you go straight (up), it shouldn't be any problem.

Jake_Blues

It turns off the electronic stability (roll & spin mitigation) but doesn't disable the brake-lock differentials.

Both front tires DON'T want to spin at the same speed. They want to spin at different speeds, and as long as you haven't locked up your diff, they CAN spin at different speeds. This isn't the problem.

The problem is that your front drive shaft MUST spin at a speed that is the average of the speeds of the front left and front right tires. So if you're going around a corner at an average speed of 10mph, your right front might actually be traveling at 11mph and your left front at 9mph. Because of the way a differential works, your front drive shaft will be spinning at a speed that would make the Jeep go 10mph (11+9/2), even though the wheels are not moving at this speed. This is perfectly OK and will happen regardless of whether you're in 4wd or 2wd, that is what a differential does.

The problem is that on that same corner, your rear wheels might be traveling at 10mph and 8mph, for an average of 9mph that the rear drive shaft needs to make revs for.

Now, your rear driveshaft wants to spin revs for 9mph, and your front driveshaft wants to spin revs for 10mph. When you're in 4wd, this difference is transmitted directly to the transfer case, and binds everything up until something slips (either the front tires "push" or the rear tires "pull") or, eventually, something breaks.

In an "AWD" or "Full Time 4WD" transfer case, the front and rear drive shafts aren't mechanically linked and can spin at different speeds, so this binding doesn't happen.

-E

Rubidonn

You got me there... great explanation... I learned something new today... So if I read correctly, this is causing the stearing jerking/jumping and where I mentioned being 'fully locked'... that is due to something different... the differential not allowing the tires to spin at different rates, correct?

Lucas718

Mine is a 2003 KJ, so there is no ESP on it. KJ's (at least in 2003) have Command Track and Select Trac. I forget which is which, but I have the part-time 4wd option. I figure it's fine to use just to get me moving instead of sitting there spinning the rear wheels. I'm usually not even all the way through the intersection before I switch back to 2wd.

John L

One word. Snow. I got to use 4HI a few weeks after I bought the JK in the snow, no problems at all getting around town. Went to the fairgrounds parking lot and played some....OK, I played a lot...with all the different modes of forward travel, it was a learning experience with the computer wanting to drive some of the time.

Rubidonn

VERY good advice... everyone should probably get out during the first good snow and understand what driving their JK means w/all the computer assisted stuff going on.

I haven't done this yet, but indeed will. Haven't driving a vehicle like this before w/all the computer assisted stuff going on. Should be interesting. I'm kind of old fashioned when it comes to that stuff and always 'like to feel the road' below me... but from what I understand, this $hit really works... I just need to get out and play around with it to understand when I'm supposed to 'not fight' the computer and let it do its thing.

Jake_Blues

Bingo. When your diffs are locked, the right and left tires on each axle are forced to go the same speed. You can still run into the situation described above, because the front tires still want to go the speeds as described above, but now you have the locked diff preventing the front set of tires and rear set of tires from spinning at different speeds (basically a solid axle). What usually happens then is that the inner wheel goes the speed it "wants" to go, and the outside wheel scrubs, slides, and chirps around the corner.

Basically, the answer is never run part time 4wd (or use your lockers) in high traction situations.

I don't know about the JK, but many 4wd vehicles don't even run the same gear ratios in the front axle as the back.

By the way, there is also another issue with steering/front end jerkiness, and that is U-joints. I won't even get INTO that mess, but read up on constant velocity joins vs regular u-joints if you're curious

-E