This is really more a hypothetical question than IRL but I'm curious as to the correct procedure in case I find myself caught in this scenario (which is a little more likely than you might think).
Case #1: Assume a 2006 Ram 1500 4.7L with manual 6 speed transmission, electronic 4WD engagement and available 4WD Lock.
Case #2: Assume a 1997 Jeep TJ 2.5L with manual 5 speed transmission and manual transfer case 4WD engagement.
- On a hypothetical 'wet grassy/muddy slope', I would be coasting downhill in neutral to gain some forward momentum then shifting to 2nd or 3rd before dropping the clutch and transferring forward motion to the engine¹.
- The hypothetical 'wet grassy/muddy slope' has a low enough traction coefficient that travelling up the hill would necessitate 4WD.
- The Dodge's battery is sufficiently depleted to be unable to start the vehicle while still having enough charge to maintain an electronic 4WD engagement² as it would have been driven up the hill in 4WD. It doesn't matter what stage of charge the Jeep's battery is in.
I'm assuming that in both cases, the 4WD would have to be active before the roll was initiated. The Jeep transfer case should be engaged at a standstill and the Dodge's electronic shift to 4WD takes a few seconds that you wouldn't want to be worried about when rolling down a hill.
I get that initiating a roll downhill in 4WD is going to require additional effort to gain the same forward momentum as in 2WD but conversely, I believe the added 'moving parts' will contribute a form of pseudo-flywheel effect.
If I'm trying to 'bump start' either of the above vehicles coasting down a wet grassy/muddy slope, should I be in 2WD or 4WD before dropping the clutch?
¹ 4WD-Low (Bull Low) doesn't really enter into these scenarios from my perspective but comments/answer responses to the contrary are welcome.
² Having never personally engaged an electronic 4WD on a partially dead battery and a engine that isn't running I am only assuming that it can be done.