No worries! it's a great question. Here's what I understand about what Auto tranny's do for your crawl ratio.

in an auto tranny, the engine is turning more revolutions' than the main-shaft because of the torque converter, so the effect is that of a reduction gearset UNTIL the torque converter locks up then it's a direct 1:1 ratio (which is fine, since at higher speeds/RPM's, you'll likely do fine with a 34ish:1 crawl ratio in 4Lo.)

Up until lock-up, depending on the transmission model, most folks I've talked to agree that the reduction ratio can vary (even in the same vehicle based on throttle input/speed) from 1.5-2.0:1 (hence the 1.8:1 number I used.)

So that's why for an manual you have

trans 1st gear: ___
Tcase #1 low:2.52
crawl box(if any):__
Axle gears:3.73

and for an auto you'd have

Trans first gear:3.52
Auto reduction: 1.5-2.0
Tcase low #1:2.52
Crawler box (if any):__
Axle gears:3.73

4x4's with auto's can get away with a transmission first gear that is lower numerically/steeper than their manual tranny counterparts while acheiving the same "Effective" crawl ratio offroad.

For example the JL 8 speed first gear is 4.71:1, and the manual is 5.13:1 but both seem to achieve the same 75-85:1 crawl ratio in 4Lo.


That's what i understand and have experienced offroad. Might be that other folks on the board can delve deeper.