4WD Auto questions

[AFD]

Should you change modes while moving or when stopped? Does it matter (as long as it's relatively lower speed like below 50mph)?

Think the manual states stopped or "up to" 45MPH for changing into 4HI (or 4HI-AUTO) from 2WD, though I've seen older official videos/documents state to do so below 55MPH. You can drive above those speeds in either 4HI mode. Changing into 4LO should be done either stopped or at a slow 1 to 3MPH roll with the clutch depressed or in neutral with a max speed of 25MPH, iirc.

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[RecessRampage]

Think the manual states stopped or "up to" 45MPH for changing into 4HI (or 4HI-AUTO) from 2WD, though I've seen older official videos/documents state to do so below 55MPH. You can drive above those speeds in either 4HI mode. Changing into 4LO should be done either stopped or at a slow 1 to 3MPH roll with the clutch depressed or in neutral with a max speed of 25MPH, iirc.

Thanks!

 

[GATORB8]

The 4xe and 392 have full-time 4WD, but not a selectable 2WD. The Selec-Trac and Rock-Trac full-time 4WD option (now discontinued, iirc) has 2HI, 4HI-AUTO, 4HI and 4LO.

Watch the video I posted above. They're very similar, but different.

Just the 392 doesn’t have 2, 4xe does.

 

[AFD]

Selec-Trac is Jeep's name for what you and others are calling "4WD auto transfer case".

Just to clarify, they also have (had) a Rock-Trac "full-time 4WD" option that's similar to the Selec-Trac system (non-392/4xe "full-time 4WD" with 2HI and 4HI-AUTO modes). Think the only reason we call it "4WD Auto" is to better differentiate it between the 392/4xe version.

I have the Rock-Trac w/4WD-Auto and I'm pretty dang sure I do have a F.A.D. since I think the bushing now needs replaced.

 

[TheRaven]

"For variable driving conditions use 4H AUTO which engages the front axle but sends the vehicle's power to the rear wheels. If the vehicle senses a loss of traction, it automatically engages 4WD. Because the front axle is engaged, this mode gets lower fuel economy than 2H position."

Thank you sir.

So it's physically engaged but effectively disengaged. This tracks actually...this afternoon I was reading up on the Auto 4WD in my Silverado and it's the same - physically engaged but not doing anything. To bring this full circle to my original comment that caused this tangent, this means that you definitely SHOULD NOT leave Auto 4WD on all the time. That's going to result in quite a bit of extra wear.

 

[jac04]

... this means that you definitely SHOULD NOT leave Auto 4WD on all the time. That's going to result in quite a bit of extra wear.

Are you thinking the clutch system in the transfer case is going to experience extra wear, or other components?

 

[Wbino]

I've also come to find out if you have Selec-Trac that if you're in 4auto and you give it 30% or more throttle it kicks in automatically.

 

[Mr.Wilson]

When in 4WD auto all 4 tires are able to spin at different speeds. Perfect for any road conditions driving straight or around corners. Similar to an all wheel drive car.
When in 4WD Part Time (Command-Trac) all 4 tires spin at the exact same speed. Good for getting out of a jam. Definitely will cause binding while turning.

 

[TheRaven]

Are you thinking the clutch system in the transfer case is going to experience extra wear, or other components?

All of the above...the clutch is always slipping when the system is on so that's obvious, but also the shock to the axles, diff and joints when torque is vectored to the front wheels. This effect is well documented in the GM truck world - aftermarket companies warn against using Auto 4WD with lifts beyond a certain height because of the shock experienced by the CVs when the system sends torque to the front wheels. Guys who were otherwise having no issues were ending up with broken CVs after using Auto 4WD.

 

[Ratbert]

When in 4WD Part Time (Command-Trac) all 4 tires spin at the exact same speed. Good for getting out of a jam. Definitely will cause binding while turning.

Are you thinking that your front and rear diffs are locked just because you're in 4wd part time?

 

[Mr.Wilson]

Are you thinking that your front and rear diffs are locked just because you're in 4wd part time?

Part-time 4WD operates by default as a two-wheel drive vehicle. Unlike the full-time system, part-time 4WD doesn’t use a center differential. The system instead locks the front and rear wheels, making it optimal for use during off-road travel or challenging road conditions. When on dry pavement or under normal driving conditions, the driver should switch to the vehicle’s two-wheel-drive mode. If drivers use part-time 4WD excessively, they may experience driveline noise or binding that can lead to damage or early part failure.
WARNING-Part-time 4WD locks the front and rear axles together so the front and rear wheels turn at the same speed. If attempting to turn or drive on dry surfaces, binding (crow hop) and driveline noise (a bang or shudder) will occur, which can lead to early part failure.

 

[Ratbert]

Part-time 4WD operates by default as a two-wheel drive vehicle. Unlike the full-time system, part-time 4WD doesn’t use a center differential. The system instead locks the front and rear wheels, making it optimal for use during off-road travel or challenging road conditions. When on dry pavement or under normal driving conditions, the driver should switch to the vehicle’s two-wheel-drive mode. If drivers use part-time 4WD excessively, they may experience driveline noise or binding that can lead to damage or early part failure.
WARNING-Part-time 4WD locks the front and rear axles together so the front and rear wheels turn at the same speed. If attempting to turn or drive on dry surfaces, binding (crow hop) and driveline noise (a bang or shudder) will occur, which can lead to early part failure.

Ok, let me try again. Do you think that your front and rear diffs are locked just because you're in 4wd part time? That's the only way I'm aware of where all four tires could spin at the same speed when turning.

 

[Mr.Wilson]

Ok, let me try again. Do you think that your front and rear diffs are locked just because you're in 4wd part time? That's the only way I'm aware of where all four tires could spin at the same speed when turning.

I would assume so. That’s the only possible way it would work.

 

[AFD]

 

[TheRaven]

I would assume so. That’s the only possible way it would work.

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.

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