4WD Auto questions

[Mr.Wilson]

That's not what that explanation was saying. 4WD HI locks the front and rear DRIVESHAFTS together, so they spin at the same speed and transmit the same amount of torque. That does not mean that the wheels on the left side are getting the same torque as the wheels on the right, unless you have lockers like the Rubicon does. The diffs still transmit torque the way they do under all circumstances.

4H Part Time locks the front and rear axels causing them to spin at the exact same speed.

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[TheRaven]

4H Part Time locks the front and rear axels causing them to spin at the exact same speed.

DRIVESHAFTS, not AXLES.

 

[Mr.Wilson]

DRIVESHAFTS, not AXLES.

We can agree to disagree all day but this is directly from JEEP. So maybe they don’t know what they’re talking about. Who knows.

 

[TheRaven]

We can agree to disagree all day but this is directly from JEEP. So maybe they don’t know what they’re talking about. Who knows.

You are reading more in that description than is actually there. That's a description written by a marketing team.

There is a clutch in your transfer case that manages the connection between your transmission and driveshafts. In 2HI the clutch is fully disengaged and 100% of the power produced by the motor through the transmission is sent to the rear driveshaft. That power is transmitted through the diff in a method consistent with the type of diff it is. But the ONLY time that that power is split evenly between both rear wheels is when a locker is engaged. From the factory, only the Rubicon is equipped with lockers, and they are engaged by the driver as needed. The front axle works the exact same way, so when you engage 4HI, that clutch in the transfer case engages fully and sends 50% of available power to the front driveshaft.

So again, the ONLY example where all four wheels are receiving the exact same amount of power is in a Rubicon with lockers engaged in 4HI or 4LO. If you are in a Sport or Sahara, the front/rear split is 50/50 but the diffs are distributing torque based on traction in a manner consistent with their design (so it depends on whether you have the LSD or the BLD diffs) The transfer case can only control the split between the front and rear driveshafts, it cannot do anything about the split between left and right axles.

 

[Ratbert]

We can agree to disagree all day but this is directly from JEEP. So maybe they don’t know what they’re talking about. Who knows.

No, you're acting like you understand all of this from reading the owner's manual. Sorry, but you're clearly mistaken if you think that engaging 4hi locks all four wheels to the same speed. You understand what lockers are, right?

 

[Mr.Wilson]

No, you're acting like you understand all of this from reading the owner's manual. Sorry, but you're clearly mistaken if you think that engaging 4hi locks all four wheels to the same speed. You understand what lockers are, right?

Yes I do and if I’m wrong then im wrong. I’m just going by what I read. If it’s wrong then ok. Now I know.

 

[Ratbert]

Yes I do and if I’m wrong then im wrong. I’m just going by what I read. If it’s wrong then ok. Now I know.

Lockers do what you described from a left / right perspective. If that was in place with normal 4wd then turning would be stupidly difficult (and potentially damaging), especially with the fronts locked.

 

[Xtina]

I just came here to say the 4wd auto is literally the best and should be on all wranglers. It works amazing and you don't even notice it engage. It's smooth as butter. My old jeep had me constantly switching from 2 to 4 for snow patches (because Alberta doesn't know how to plow a road) and it was such a hassle.
The 4wd auto and etorque are my favorite things about my new wrangler.

 

[Yawnie'sPapa]

Under heavy throttle, the clutch get more pressure - regardless of road speed or wheel slip, etc.
If you use 4HA in a 4xe and nail it you can feel a big difference between that and nailing it with it in 2H because the torque is limited unless you are in 4HA.

somewhere I have another showing that when it's sitting, 0 mph, no throttle - the clutches are applied.

 

[Yawnie'sPapa]

I just came here to say the 4wd auto is literally the best and should be on all wranglers. It works amazing and you don't even notice it engage. It's smooth as butter. My old jeep had me constantly switching from 2 to 4 for snow patches (because Alberta doesn't know how to plow a road) and it was such a hassle.
The 4wd auto and etorque are my favorite things about my new wrangler.

4HA is great for snow plowing. I can turn hard in tight areas even with some wheels on bare pavement, it just doesn't slip and doesn't jump around. Smooth as heck. I can even plow up-hill without issues.
4H part time is not fun for plowing in my area with the tight turns and here and there bare pavement.

 

[rforbes]

Does it do any damage to leave in 4 auto all the time. I ask because wife drives and I doubt she will remember to go back and forth

That's how I run mine. in 4H Auto pretty much all the time.

 

[rforbes]

Yes I do and if I’m wrong then im wrong. I’m just going by what I read. If it’s wrong then ok. Now I know.

it's not so much "wrong" as misleading. I think the easiest way to think about it is 4H locks front to back and lockers lock left to right.

 

[Mr.Smith]

That's how I run mine. in 4H Auto pretty much all the time.

Yeah I have done some 2wd and some 4h auto and I don't see a difference in mpg

 

[Bzinsky]

4auto is AWD, there is no difference. This is my second vehicle with it, my previous was a 2014 gmc 1500 and it functioned the exact same way. I’ve explained it multiple times these forums exactly how it works and how the transfer case functions exactly the same as a clutch based awd center differential.
Having a center diff = awd
Having a lockable transfer case = 4wd
Having both = for some stupid reason they call the awd setting 4auto. (Even though in a lot of GM vehicles with 4auto they call it “awd” right in the gauge cluster)

You can leave it on 24/7, you’ll take about a 3-5% efficiency hit.

I leave it on 24/7 in my 4xe just because they limit boost in 2wd. If I had a 2.0 or 3.6, I’d probably leave it in 2wd just because it’s wasting a little fuel.

 

[TheRaven]

4auto is AWD, there is no difference. This is my second vehicle with it, my previous was a 2014 gmc 1500 and it functioned the exact same way. I’ve explained it multiple times these forums exactly how it works and how the transfer case functions exactly the same as a clutch based awd center differential.
Having a center diff = awd
Having a lockable transfer case = 4wd
Having both = for some stupid reason they call the awd setting 4auto. (Even though in a lot of GM vehicles with 4auto they call it “awd” right in the gauge cluster)

You can leave it on 24/7, you’ll take about a 3-5% efficiency hit.

I leave it on 24/7 in my 4xe just because they limit boost in 2wd. If I had a 2.0 or 3.6, I’d probably leave it in 2wd just because it’s wasting a little fuel.

This is not necessarily true. There are several types of AWD that do not have a center diff. A lot of AWD BMWs, Audis, Cadillacs, and Lincolns have a "transfer case". The aforementioned "Haldex" system actually uses neither a center diff nor a transfer case.

Effectively the difference between "AWD" and "Auto 4WD" is the torque split when there is no wheel slip. For AWD, there is always some torque being applied to the non-primary wheels, with Auto 4WD, there is no torque applied without wheel slippage.

As discussed, slightly reduced fuel mileage and greater wear on drivetrain components will result from always using Auto 4WD.

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