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Old 11-05-2018, 07:04 AM   #1
moodman
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Differential Ratios

I have a 2003 RAM 3500. I believe it has a differential ratio of 3:73. My question is "What advantage will I get by changing the differential ratio to a 4:10"?

My goal is to be able to more easily tow my 14,000 pound 5er. My truck handles it now, but only barely. Will I get a substantial boost in capacity by changing my ratios?

Also, it seems to me that a lower ratio, like 4:10, will be easier on the transmission. Is that true?
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Old 11-05-2018, 07:40 AM   #2
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Differential Ratios

4:10 is actually a higher ratio. Your RPMs will increase to maintain the same speed. Will it be easier on the engine? Depends on your driving style. It will be easier to get up to speed, it will probably be a little easier to yank 7 tons UP the hill in lower gears, you’ll just be crawling like I do.
Substantial boost in capacity? Probably not.
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Old 11-05-2018, 08:01 AM   #3
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As Chuckster said, probably not. A lot of money for a sixteen year old truck. 4WD? Twice the money.
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Old 11-05-2018, 08:03 AM   #4
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Maybe I wasn't clear on my OP. I know that I can't get more capacity on how much pin weight it can carry. I am wondering if I can actually tow a heavier weight. Some number I have seen boost this as much as 2,000 pounds or more. Just wondering if that is realistic.
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Old 11-05-2018, 08:05 AM   #5
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Axle gear selection, especially with older 3 or 4 speed transmissions is limited more by the transmission capability than by the engine.

Most vehicle manufacturers select axle gear ratios that work best with their engine/transmission selections. Keeping the engine RPM in the "power/torque curves" is their main consideration. With the older transmissions, changing a 3.73 gear set for a 4.10 gear set may or may not give you the capacity to keep the engine RPM "in the power/torque range" at the speeds you will want to drive.

While the higher gearing will give you more "acceleration off the line" and "improved hill climbing capability" in most situations, you also need to assess how it will affect your "other driving situations".... Can you maintain the speed you normally tow with the engine in the RPM range to maintain good economy AND performance? Will the increased RPM from the higher gear set cause your fuel mileage to decrease or increase when towing on "flat ground"???

It's good to gain the "umph" to climb hills and accelerate faster from a stop, but is the change worth the expense of the axle changeout and the loss of MPG in the majority of towing situations?

I suppose it comes down to the overall question: Is the slight increase in performance in some situations worth the expense in MPG for the rest of my towing environment?
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Old 11-05-2018, 08:32 AM   #6
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I agree with the above, may be very costly for marginal improvement unless that is the one limiting factor.

Top highway cruising and fuel economy are moot issues, usually mutually exclusive.

But in **selecting** a truck to purchase, 4.10+ will get you an overall much better towing drivetrain package
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Old 11-05-2018, 08:39 AM   #7
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Quote:
Originally Posted by John61CT View Post

But in **selecting** a truck to purchase, 4.10+ will get you an overall much better towing drivetrain package
So, back to my original question, how much better will it be? I'm not as concerned with fuel economy. More interested in getting it up the hills and maintaining speed at freeway speeds, instead of having to slow down on every hill on the interstate.
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Old 11-05-2018, 08:43 AM   #8
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Having had a 97 F350 7.3 with factory 4:10 gears I can say you will still be lacking. While the 7.3 was programmed up 100 ft/lbs and 80 hp over stock, it still struggled with my toy hauler on the hills. The transmission is the weak point in this truck and in yours and I was afraid I would blow another one if I took it to the mountains with that kind of load. So I went to the 6.7 with the 6 speed auto and oh what a difference! Save your money and move up to a more capable truck. The old ones could get the job done, and still do. But if you want effortless power and torque you will have to upgrade.
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Old 11-05-2018, 10:00 AM   #9
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Quote:
Originally Posted by moodman View Post
So, back to my original question, how much better will it be? I'm not as concerned with fuel economy. More interested in getting it up the hills and maintaining speed at freeway speeds, instead of having to slow down on every hill on the interstate.
The only way to get an absolute definitive answer is for you to hitch up with your current set up and head for the track. Document your 1/8 and 1/4 mile times and speed. Then head for a hill and start at the bottom and document the speed and time to reach the top. Go home, change out the gering and repeat. And each test must be with the accelerator applied ax max (i.e. floored).
No one can answer your question as it's impossible to know how you drive, the gradient and distance of the "hill" etc. For anyone to say they changed theirs out and it made a "big" difference is like stating that the new facial soap makes them look better.
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Old 11-05-2018, 10:07 AM   #10
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Totally agree that the transmission is the weak link in my truck. But, my 5.9 Cummins has a lot of latitude in it to get more power out of it with upgrades.

With the transmission, does anyone know if the Aisin transmission can be bolted to the 5.9 Cummins? If so, then I could swap out to an Aisin and then mod my engine to get the power I need.

The whole reason for asking about the differential was to determine if that would be the best place to cheaply get more torque for towing. If not, then I should concentrate instead on the engine and tranny.

And, BTW, the specs for my engine are about 300hp and 500 lb/ft of torque.
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Old 11-05-2018, 10:49 AM   #11
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You would be better off from a financial standpoint to upgrade your current tranny. Your tranny can be upgraded to be a lot stronger than the Aisin for less money. If you haven't already, do some tranny research on the Cummins forums.
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Old 11-05-2018, 02:09 PM   #12
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I will be like adding 50 ft.lbs. of torque & 200 rpm if your cruise rpm is 2000.
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Old 11-05-2018, 04:04 PM   #13
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I'm trying to figure out your ultimate game plan. It sounds as if you want to upgrade the towing capacity/longevity of your truck to something like new. Obviously that won't happen.

The observation about the tranny being the weak point is on point IMO. Rebuilding the 5.9 so that it produces 750 lbs. of torque running thru the old tranny will just put you on the side of the road. Changing the ratios (and I've done several) has lots of benefits but I'm not sure if it would accomplish what you want. It will, by the book, increase your "tow capacity" by 2000 lbs. What does that actually mean? Your truck is maxed out at 14k. It is 16 years old. You've said it struggles with the trailer. The increased rpm from the new ratio will spin the engine harder and shorten its life - all trade offs. I don't know if the Aisin can be adapted to your truck. I do know that I've had multiple trannies "upgraded", "strengthened", made "heavy duty" etc. to no avail. I usually blew them out under hard use. When you start the rebuild game and upgrading this or that.....it just keeps on going as you try to make everything else work with what you've done.

By the time you put in a new tranny, install new ring and pinions (last time cost me $2400 several years ago) and upgrade the engine you will have spent many thousands....and still have the running gear/suspension/interior/electronics etc. of a 16 year old truck. It doesn't compute to me. Here are the towing specs of your truck;
http://dodgeram.info/2003/load-tow/3500SRW.html

Good luck in picking a path....they can be very expensive.
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Old 11-05-2018, 04:48 PM   #14
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moodman Siding with Danny on this. I have also been done the upgrade road many times and always come to the same conclusion it becomes a money pit. Not saying your idea would become that. JMHO YMMV
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Old 11-05-2018, 04:48 PM   #15
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Yes invest energy into getting the best price selling this one, and finding a great deal on the next one.

The price differential will likely be lower cost, and the result more certain
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Old 11-05-2018, 04:49 PM   #16
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Had an 01 F350 with 3:73 gears and went to 4:30 front and rear. Made a world of difference pulling my 5ver. Just going to 4:10's would not have made much difference.
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Old 11-05-2018, 05:13 PM   #17
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That's good advice. Thanks.
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Old 11-05-2018, 05:27 PM   #18
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Keep in mind, if you are planning to up the horsepower and torque to the level of current diesels there would be no point in wasting money on the differentials. My current truck has 3:73's and has NO problem hauling 18000 lbs. uphill and holding 65-70-75 mph with the cruise on. Seldom shifts down out of 6th gear. I had considered going that route with my 97 as I really liked that truck and it was super clean for it's age. But one of the deciding factors was the lack of availability of parts in the later years. Interior panels, seat parts, fuel tank sending units, things that you had to look for in wrecking yards and often were no better condition than the part you were trying to replace. I can relate to what you're looking to accomplish, I really can. But I'm happy with the decision I made. Good luck in your endeavor.
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Old 11-05-2018, 06:23 PM   #19
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Just to clarify one thing, the higher the number means the lower the gear. A 3:73 ratio is higher geared than a 4:10 ratio.
My 2008 Cummins 2500 has 4:10 gears and it works very well pulling my 5th wheel. It seldom shifts down on hills. The trade off is 2k rpm's at 70 mph and 2,300 rpm's at 80 mph. So I try keeping it around 70 on long interstate runs. Of course I'm being passed a lot.
With that said I agree with others saying the best way to go would be to upgrade to a newer truck. Modifying an older vehicle ends up to be a money pit.
Heck, all vehicles are money pits, but with an older one the money just goes faster with less return. Good luck.
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Old 11-06-2018, 03:15 AM   #20
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You all educated me very well. Now I have some thinking to do!

Thank you
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