Originally Posted by Thunderhorse
Yes you should get what you're promised, but y'all need to realize that the final drive ratio on an 8 speed ram with 3.21 diff in 1st gear is 15.12:1. With a 4.10 and the 6 speed tranny its 12.3:1. I think a lot of the hate for the 3.21s is fed by those with the 6 speed where the 3.92 diff made a big difference, but the bottom line is that if a 6 speed truck with 3.92s was good enough for you, an 8 speed with 3.21s will actually be an improvement. Now you do get an 18.46:1 1st gear final drive ratio with an 8 speed and 3.92s, but the point of the post is to demonstrate the adequacy of the 3.21 with the 8 speed.[/QUO
Without straying too far off topic, how could an 8speed with 3:21's be an improvement over a 6 speed with 3:92's? Granted the 8 speed splits the power up more on the way up shifting, but you are still ending up with a taller final drive gear. You can't pull the same weight with the 3:21's........
unless I'm not understanding something.
Despite the fact that the differential is geared lower on a 6 speed with the 3.92, the first 2 gears (4.71:1 and 3.14:1 respectively) in the 8 speed transmission are both lower than the first gear in the 6 speed (3.0:1). The 8 speed has a greater overall range (4.04 vs 2.33 in the 6 speed), so you have a greater multiplication in lower ranges.
The 2nd gear of the 6 speed is the same as the 4th gear in the 8 speed (1.67:1); The 4th gear in the 6 speed is the same as the 6th gear in the 8 speed (1.0:1); and the top gear in both transmissions is the same (0.67:1). Because of this, a Ram with the 3.21 has a final drive ratio of 2.15:1 in its top gear vs the 2.63 ratio of the 3.92, while still having a lower ratio in first gear than the 3.92 with the 6 speed due to the greater range of the gearing in the transmission that having 8 gears affords. Despite this, the gears are still spaced closer on the 8 than the 6 which means you don't get the infamous "dead spot" that the older transmission was known for.
I have to agree with TJC.geotech as well. My 8 speed with 3.21 shifts out of first gear at around 5-7 MPH so I don't think the 3.92 would provide too much benefit. Maybe if you plan on lifting, or you like shifting into 2nd at 3MPH.
As far as towing is concerned, it can be a variety of things that limit capacity. For example, it turned out that the V6 trucks with the 8 speeds needed the parking pawl strengthened. Also, while it may be true that you have a taller top final drive ratio with the 3.21 than the 3.92 (2.15:1 vs 2.63:1), if you were to be towing in 7th with the 3.21 puts you at 2.69:1 which is negligibly different to the ratio with the 3.92. There has been some discussion on this forum (I think in the 2014 GD section) that they may be increasing the ratings for V8 8 speed trucks for 2014+ and retroactively for the 2013s similar to what they did with the 2010+ Ram 1500s (retroactively for the 2009s). As far as I know its just hearsay though.
ETA: Don't get me wrong, if you ordered a truck with a specific diff you absolutely should get a truck with that ratio. But in my opinion those who dog the 3.21 8 speed without driving one need to test drive one and see if they still feel the same. A lot of what you may feel is a tall diff may actually be the traction control nannies killing your power, so try turning that off too.