Auto trans 68RFE in 2014 Dodge Ram 3500 adequate to tow 17,000 lb. Big Horn 5th Wh??

[Powder Extreme]

My 3/4 ton 3.42 is substantially better than my 1 ton 3.73, about 3-4 mpg. But the 1 ton has them big ole child bearing hips. Hard to say how much is gears and how much is tires.

 

[Camperman]

My 2012 has the 68RFE, and I'm happy with it. Our 5er comes in at 15,000lbs loaded. I have 4.10 gears, and I recommend them. My sold truck, a 2006 F-350 dually had 4.10's as well. If I understand correctly, the 4.10 is only available with the Aisin transmission option, and may be limited to a dually configuration. I can tow up a 6% grade and hold 60 mph in 5th gear.

 

[Cummins12V98]

At three different RPM's for the same speed, its a no brainer, 3:42 is like climbing a perpetual grade, compared to 4:10's.

There is more to my question. Let's say all three ratios are in 6th cruising at 55 running solo. The 4:10 may get better mileage since it may be in its "sweet spot" ??? The 3:42 may get worse because it is below it's Sweet spot and uses more fuel to maintain it's speed.

 

[Joseph Donnelly]

I have the "other" automatic with 3.42, but the software is calibrated so if there is very little load, the trans will be in 6th for economy, but will downshift if more power is needed, whether at 55 or 65 mph. I briefly tried locking out 6th vs. letting it upshift and downshift as the software wanted, on similar rolling hills. Mpg on EVIC was better letting the computer pick the right gear. Therefore, I would not fret with 3.42s unless you have a very heavy trailer that calls for more gear, mostly to get it rolling from a stop.

 

[Bug Out]

I tow a 17K 5th wheel and have been very impressed with the 3:42's and 68 RFE. Has no issues pulling hills etc. I leave it in 5th gear most of the time as I tow around 60 MPH, unless on real flat hwy.

If you have a option, by all means get the aisin.

 

[Bug Out]

Powder Extreme, I got a good laugh out of , " But the 1 ton has them big ole child bearing hips"... My 12 year old called my Dually, "The truck with the big BOOTY".

 

[PC12Driver]

Interesting philosophy in support of 3.42 gearing, but personally I'd rather have 6 than 5 gears available when towing the 5th wheel in my signature. Also, a slower turning driveline means that all the components upstream of the ring gear are having to transmit more torque for a given rear wheel torque and speed. Since BHP = (Torque x RPM) / 5252, then a decrease in driveline speed means a proportional increase in driveline torque for a given rear wheel horsepower and speed. There's a reason that rated GCWR increases as differential gearing goes lower (higher numerically).

If 4.10s in 6th turn the engine the same RPM as 3.42s in 5th, then the engine "sees" the same torque. The only components that are under more torque are the driveshaft and some parts of the transmission. And considering that the driveline can handle thousands of ft/lbs of torque (max engine torque x first gear reduction x 4-low reduction), a 50 ft/lbs of torque difference in cruise is a wash. Plus, you'd be putting that extra torque on larger diameter gears (pinion, transmission), so wear-wise, you'd probably come out ahead with the numerically lower gears.

The GCWR covers all situations that a truck might experience. Dragging a camper down the road is a pretty easy life for these trucks, considering trucks with half the power can do the same thing. Put them in a different scenario, such as dragging 1,000 gal fertilizer tanks around soft farm ground, and you'll see higher engine and trans temps than you'll ever see with a camper in tow. That's where the GCWR limit actually means something.

 

[Powder Extreme]

Powder Extreme, I got a good laugh out of , " But the 1 ton has them big ole child bearing hips"... My 12 year old called my Dually, "The truck with the big BOOTY".

Lol! The girlfriend is dying over "the truck with the big Booty"

 

[RVTRKN]

If 4.10s in 6th turn the engine the same RPM as 3.42s in 5th, then the engine "sees" the same torque. The only components that are under more torque are the driveshaft and some parts of the transmission. And considering that the driveline can handle thousands of ft/lbs of torque (max engine torque x first gear reduction x 4-low reduction), a 50 ft/lbs of torque difference in cruise is a wash. Plus, you'd be putting that extra torque on larger diameter gears (pinion, transmission), so wear-wise, you'd probably come out ahead with the numerically lower gears.

The GCWR covers all situations that a truck might experience. Dragging a camper down the road is a pretty easy life for these trucks, considering trucks with half the power can do the same thing. Put them in a different scenario, such as dragging 1,000 gal fertilizer tanks around soft farm ground, and you'll see higher engine and trans temps than you'll ever see with a camper in tow. That's where the GCWR limit actually means something.

An easy example in laymen terms over the difference from 4:10 vrs 3:42 would be a lever that is 2ft long to turn a gear under load will turn it easier than a 1ft lever turning the same load. It will take more effort to turn the 3:42 gear set. When the truck is at its lightest, it is not noticeable, but when loaded at Dodges maximum advertised GCVWR, that 1ft lever will take more torque to turn it than a 2ft lever and be noticeable when climbing grades. Even if your not climbing grades, under heavy load it will take more effort to move the 3:42 gear set and that will be reflected in your MPG.

 

[PC12Driver]

An easy example in laymen terms over the difference from 4:10 vrs 3:42 would be a lever that is 2ft long to turn a gear under load will turn it easier than a 1ft lever turning the same load. It will take more effort to turn the 3:42 gear set. When the truck is at its lightest, it is not noticeable, but when loaded at Dodges maximum advertised GCVWR, that 1ft lever will take more torque to turn it than a 2ft lever and be noticeable when climbing grades. Even if your not climbing grades, under heavy load it will take more effort to move the 3:42 gear set and that will be reflected in your MPG.

True, except the transmission adds a second "lever" between the power source and the load-

4.10s in 6th: 4.10 x .63 = 2.58 final drive
3.42s in 5th: 3.42 x .82 = 2.80 final drive

Actually, the 3.42s in 5th have a longer "lever" for cruising, which is where you'll spend most of your time dragging a camper around. So, all else equal, the engine will need to produce less torque with 3.42s in 5th.. As far as comparing MPGs, I get low to mid 9s in 5th and a touch over 10 in 6th with the camper in tow @ 65 mph, so that's about 1\2 - 3\4 mpg better with 30% more torque on the engine.

Obviously there's a place for the lower gearsets, but I don't think pulling even some of the largest campers on the highway means an automatic check mark by the 4.10 box on the order sheet. These trucks make so much torque that they can pull 99% of the available 5vers up 99% of the grades on US highways and not drop below the posted speed limit with any of the available gearsets. If heat buildup from an unlocked TC or not being able to accelerate was an issue, then certainly a lower gear set is called for. But that doesn't happen pulling campers down the highway with the latest generation of trucks.

 

[RVTRKN]

Its all arguable about the MPG due to driving habits, fuel quality, gear sets, tire size and type, transmission, and terrain. But the law of physics are at play with the different gear sets, no mater what you do, to make the engine and transmission do to move the load, the levers that turn the gears remain the same. So if you have a 3:42 gear set, I would worry about excessive wear and heat, while the 4:10's will run cooler and have less wear.
If I was stuck with the 3:42's, I would service the diffs more often and monitor the temps and install a better cover designed to remove the heat generated easier than the stock cover.

In a hypothetical situation, if you could change the gear sets on the fly, you could tell the difference, and compare the MPG, ease of the movement and any comparison you would like to make, but we all know thats impossible. So I would stick with the law of physics that say its easier to move the load with the 4:10's, and save in fuel, if the planned operation of the truck was to run at or near the GCVWR of the truck.

I chose the 3:73 gear set because the planned operation of my truck was 50/50 (city driving/OTR trucking), but it turned out that I do 30/70 unfortunately. I wish I had ordered the 4:10's

 

[Dieselnerd]

True, except the transmission adds a second "lever" between the power source and the load-

4.10s in 6th: 4.10 x .63 = 2.58 final drive
3.42s in 5th: 3.42 x .82 = 2.80 final drive

Actually, the 3.42s in 5th have a longer "lever" for cruising, which is where you'll spend most of your time dragging a camper around. So, all else equal, the engine will need to produce less torque with 3.42s in 5th.. As far as comparing MPGs, I get low to mid 9s in 5th and a touch over 10 in 6th with the camper in tow @ 65 mph, so that's about 1\2 - 3\4 mpg better with 30% more torque on the engine.

Obviously there's a place for the lower gearsets, but I don't think pulling even some of the largest campers on the highway means an automatic check mark by the 4.10 box on the order sheet. These trucks make so much torque that they can pull 99% of the available 5vers up 99% of the grades on US highways and not drop below the posted speed limit with any of the available gearsets. If heat buildup from an unlocked TC or not being able to accelerate was an issue, then certainly a lower gear set is called for. But that doesn't happen pulling campers down the highway with the latest generation of trucks.

Let's face it, we all want to justify what we purchased. I like my 4:10's just as much as others like their 3:42's. I like cruising in 6th gear without constant downshifting or keeping it in a lower gear. I also like the fact that if I want to get a larger fifth wheel, I have enough truck to handle it.

 

[PC12Driver]

No justifying here - I've got 3.73s.

The OP asked if a 68RFE with 3.42s was adequate to pull a 17k fiver, to which the answer is a solid yes, the truck is capable. In the first post he mentioned that he would be willing to drive the transmission and put it in lower gears if needed, so the driver is also capable. And he mostly pulls in the flatlands. He'll have no problems with that combo. If he was someone who puts it in D and watches the scenery go by, then maybe something shorter in the drive axle would be a better idea.

He won't have to worry about excess wear or heat. When it comes to meshing gears, two things generate heat: rpm and load. Compared to 4.10s, 3.42s will carry 17% more torque for a given load, but they're also turning 17% slower. That's pretty much a wash. That's also 17% less u-joint flexes. If proper lubrication is maintained, there should in fact be less wear on those components. No special care or attention would be needed for the taller gearset.

If lower gears always meant better mileage, wouldn't locking the trans in 1:1 then provide better milage than either of the overdrive ratios? Obviously it doesn't, so why does that change with a trailer in tow? As long as the engine can efficiently generate enough power to move the load, fewer rpms will always return better mileage. Unnecessary rpms cause more friction between moving components, and more energy is wasted pumping unnecessary amounts of air through the cylinders. All else equal, I know my truck gets better mileage at 1,600 rpm than 1,800 rpm with my 13' high 14k lbs camper in tow. If I had 4.10s, that would directly relate to more rpms, and with the conditions I was testing in (65mph, flat ground, 5-7 mph headwind component), that would directly relate to a higher fuel consumption. Not much to argue there.

I'm not a 3.42 fanboy by any means, but I'm also not sold on the idea that 4.10s are the only answer for towing. Heck, 3.73s are rated for a higher towing capacity than anyone on this thread will probably pull. Back in the old days (3rd gen or older) I would absolutely agree that the wide-ratio 4-speed autos needed all the help they could get, and 4.10s were the answer. That's not the case anymore.

 

[RustyJC]

Back in the old days (3rd gen or older) I would absolutely agree that the wide-ratio 4-speed autos needed all the help they could get, and 4.10s were the answer. That's not the case anymore.

Back in the old days, 4.10s also got the "knock" that they were terrible for running unloaded since they buzzed the engine at insane RPMs at freeway speeds. With the double overdrive automatics (68RFE or Aisin), that's not the case any more, either. 4.10s are VERY comfortable gears to live with, either pulling our 19,000 lb GVWR 5th wheel or running bobtail.

I go back to the fact that rated GCWR goes up as gear ratios get lower (higher numerically). If you don't need the 4.10s, great, but some on this thread seem to make the argument that 3.42s are more capable towing gears than 4.10s. That being the case, wouldn't 2.80s like I once had in an early Mustang be even better than 3.42s? I hardly think so.....

Rusty

 

[PC12Driver]

If you don't need the 4.10s, great, but some on this thread seem to make the argument that 3.42s are more capable towing gears than 4.10s. That being the case, wouldn't 2.80s like I once had in an early Mustang be even better than 3.42s? I hardly think so.....

No one has said that or implied that here. If you think that's the point I'm trying to make, then you need to go back and re-read my posts and keep the thread's title and the OP's original question in mind.

 

[RustyJC]

No one has said that or implied that here. If you think that's the point I'm trying to make, then you need to go back and re-read my posts and keep the thread's title and the OP's original question in mind.

.....but some on this thread seem to make the argument.....

With all respect, did I say that you had said that? See above....I don't believe so. Some of the specious arguments presented by others, however, certainly did push that point.

Rusty

 

[PC12Driver]

Sorry for the misunderstanding. I went through the thread and didn't see any evidence of that, just a couple folks that had 'em and liked them. Figured it had to be me since I was most vocal.

 

[Wingate]

I would suggest that you look up your specific truck and adjust accordingly. There are big # differences in max trailer weight between aisin and 68 equipped trucks along with gear ratio. For instance, my truck has a maximum trailer tow rating of 20,390 lbs. with 3:42 gear ratio. that same truck equipped with the 68re is 16,660 lbs.

http://www.ramtrucks.com/assets/towing_guide/pdf/2014_RAM.3500.Towing.Specs.pdf

 

[Bug Out]

Its my belief that the 68 RFE is good up to 30 K GCVW WITH 4:10 rear gears, as the 2012 MAX tow was rated for that.(I owned one) Now, along comes 2013 and the engineers decide the 68 RFE is good enough to pull 25K GCVW with 3:42 gears which I have. I was a "doubter" until I began towing my 39' Sierra TH which puts me at near 25K GCVW.

Believe me when I say it tows my 5th just fine.(folks on this board know I was a nay sayer at first)

I happen to be mid way thru my vacation in Sacramento,ca and stumble into a retired chrysler engineer in the RV park with a Prevost Bus towing a Jeep cherokee,, worked safety systems 35 years. As we chatted about the design of the air bags in my RAM that he was a part of, I told him I wanted 4:10 gears but could only get 3:42's.He chuckled and said "believe me, with these engines you dont need them anymore".

I have to say, my only REAL BIG complaint about this truck is the shifting pattern which has a "Flare" between up shifts, 4-5-not as much with 6th. ( I know its fine by other folks)

The 68 RFE, even getting pushed as hard as I could N/B thru the Tehachapis,(Hwy 58 in s/cal) in 4th at 2500 rpm, 20 MPH headwind, it held it speed and the trans temp never got close to 190...And i had the A/C .

Even after cheer leading with the above post, SOMEBODY PLEASE COME UP WITH A RE-FLASH TO MAKE THE SHIFT PATTERN LIKE MY 2012 68 RFE !!!!!!