ROOFGOOF

I am anxious to find out what the new transmission options will do for diesel mileage...interesting indeed !

bigblock2stroke

Go to the Texas State Fair.

Berak

There is no chance at all that they spent the enormouse time, money, and effort to develop, test, and produce the 68RFE (which it turns out is not based on the 48RE but the 545RFE) just to have it be a one year option. If anything, they would drop the Aisin in the C&C trucks and have only the 68RFE available across all Rams. I don't expect that to happen either though since the Aisin has a PTO that is usually desired in C&C trucks whereas the 68RFE does not.

I guess if your suggesting that they would offer the Aisin as an option to the 68RFE, I also highly doubt that. There would be no great reason to do so.

sled4fun

I have to disagree on that. Every gear that power from one point to another point robs power and creates friction. A 1:1 output is the most efficient way to get engine power to a driveline and then to the rear differential. A small gain, but a gain that works towards better fuel economy than against it.

I think that people have just been brainwashed with the buzz word "overdrive" equaling fuel economy.

ptgarcia

Won't the gears just be a different size? You're still getting the same amount of contact points, no? Even if you're right, I'm betting you would see less than 1 mpg difference.

sled4fun

You may be right, but if you make a few changes in the direction of fuel economy it makes a big change.

PanteraGSTK

Maybe I'm confused, but I thought the reason overdrive got better milage is because it takes less RPM to go the same speed.

ptgarcia

You kind of got me wondering about this. I never really considered how gear combinations could affect fuel economy.

My Titan was setup like you described. The ring and pinion had a 3.36:1 gearset, and that was their towing gearset. Non-tow package trucks had a 2.94:1 ring and pinion. Both pretty high when compared to the domestics. The 5-speed auto transmission, on the other hand, was geared lower than the Big 3's trannies. Final drive ratio was virtually the same as the Big 3's. It seemed to work really well, but I don't know how it affected fuel economy.

HaulinBut

Ya Know.....I think you're on to something! Besides the advantages you state, when you drop the ratio of the final drive, you afford yourself the possibility of significantly increasing the strength of the unit. Doing so allows you to increase the size of the gear on the pinion shaft, decrease the size of the ring gear, and therefore the size of the pumpkin(s), increasing ground clearance, or both.
Ohh ohh....might of ran into a snag. Wouldn't this then mean that you either have more disproportinate sizing of all the driving/driven gears in the tranny?

Well, either way, I still like the idea of taking off in different gears, based on the load.

ptgarcia

Exactly. It's a tradeoff. And like my aforementioned Titan, early models had problems with differentials grenading. Some claimed it was because the pumpkin was too small for sufficient cooling.

redeyedracer

hahahah....THis was a good thread, turns out the rumor mill was right again!!! There is a dodge 6spd auto and an asian!!!! I love DTR and its members!!!