Differential Ratios

[moodman]

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?

[chuckster57]

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.

[notanlines]

As Chuckster said, probably not. A lot of money for a sixteen year old truck. 4WD? Twice the money.

[moodman]

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.

[JRTJH]

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?

[John61CT]

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

[moodman]

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.

[Badbart56]

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.

[flybouy]

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.

[moodman]

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.

[3wheeler]

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.

[77cruiser]

I will be like adding 50 ft.lbs. of torque & 200 rpm if your cruise rpm is 2000.

[sourdough]

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.

[66joej]

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

[John61CT]

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

[cpaulsen]

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.

[moodman]

That's good advice. Thanks.

[Badbart56]

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.

[fjr vfr]

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.

[moodman]

You all educated me very well. Now I have some thinking to do!

Thank you

[rhagfo]

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

I think this would be your best plan, just about what we are looking at.

[hornet28]

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.


At least one person here is knowledgeable about gears being lower or higher.

[Badbart56]

At least one person here is knowledgeable about gears being lower or higher.

I thought that was common knowledge. :ermm:

[66joej]

Back when we used call them shallow ( lower number) and deep (higher number) rear ends. Don't know if that term is used anymore.

[fjr vfr]

I thought that was common knowledge. :ermm:


Not so in some earlier posts.

[fjr vfr]

Back when we used call them shallow ( lower number) and deep (higher number) rear ends. Don't know if that term is used anymore.


Seems I remember hearing those terms a very long time ago...I think? :confused:

[jsmith948]

Back when trucks had 3 pedals on the floor boards and 2 "clever levers" to change gears, low gear was sometimes referred to as "deep reduction".
Same with a semi's brownie box - sometimes they were a four speed box, but the low gear was not progressive it was called a " double under" or "deep reduction". Sorry for the nostalgia - I loved driving those twin stick trucks:D

[66joej]

Back when trucks had 3 pedals on the floor boards and 2 "clever levers" to change gears, low gear was sometimes referred to as "deep reduction".
Same with a semi's brownie box - sometimes they were a four speed box, but the low gear was not progressive it was called a " double under" or "deep reduction". Sorry for the nostalgia - I loved driving those twin stick trucks:D

Wow that brings back memories. I used to put my left arm through the steering wheel to operate the 2 shifters in unison. And lots of double clutching. Used to call first/first the basement. Probably get ticketed for that now! No hands on the wheel.:D

[JRTJH]

Wow that brings back memories. .... Probably get ticketed for that now! No hands on the wheel.:D

You probably couldn't get your hands through the wheel (and around the air bag) on today's steering wheel..... :hide:

[77cruiser]

Back when trucks had 3 pedals on the floor boards and 2 "clever levers" to change gears, low gear was sometimes referred to as "deep reduction".
Same with a semi's brownie box - sometimes they were a four speed box, but the low gear was not progressive it was called a " double under" or "deep reduction". Sorry for the nostalgia - I loved driving those twin stick trucks:D
Wasn't a fan myself, trucking company where I worked 78-89 had 3 of them 225 Cat's in Ford dump trucks. Liked the 13 speed road ranger no clutch required.

[fjr vfr]

I don't know how you guys remember all that? :confused:
I worked for International Harvester as a mechanic back in the mid 60's up until going into the army in 68. I worked in the motor pool and drove all manner of vehicle, but I hardly remember anything from that period of life. :ermm:

It must be I'm getting really old or something. As the song goes...those were the days my friends, we thought they'd never end!
Well they did. :( It's better today...right. :lol:

[sourdough]

I don't know how you guys remember all that? :confused:
I worked for International Harvester as a mechanic back in the mid 60's up until going into the army in 68. I worked in the motor pool and drove all manner of vehicle, but I hardly remember anything from that period of life. :ermm:

It must be I'm getting really old or something. As the song goes...those were the days my friends, we thought they'd never end!
Well they did. :( It's better today...right. :lol:

I think I'm pretty close with you. Drove dump trucks for a couple of years but couldn't begin to detail what I did or how I did it....but I had fun. And, like you, I hardly remember those kinds of details from that time....but then again, I ate breakfast out this morning......hmmm, was it bacon and eggs? Oatmeal? Ham? Oh well, I made it back and got to take my nap and feel better now!:lol:

[77cruiser]

Lotsa drugs back then too.;) I can remember stuff from the 70's - 80's now where I put that, what was I looking for 5 minutes ago.:)

[oldmanbill]

Did hot shot for several years with Dodge Cummins, ratio is the most misunderstood subject. If you have the torque to get rolling you are good. A little benefit with 4.10 with automatic but not with manual. Think about it this way. Going to 4.10 gives you about 1/2 gear lower ratio. Once rolling the gearshift controls the ratio. If it is a 5 speed, 5th is weak and heavy pulling is better in 4th, direct. My favorite is 6 speed with 3.73 axle. With 5 speed it is better to stay in 4th gear, with a 4.11 you must be in OD at highway speeds. I regularly pulled over 30,000 gross weight. Still have a '99 rusting in the back yard. You will do better with larger injectors and a chip for more power.

[John61CT]

Such heavy towing in very hilly territory, or slow usage like off-road, will favor the torque advantage of a lower-geared diff.

Especially with gas engines.

But reduce highway MPG if that's a concern.

[wkdoolin]

NOOO!!!! No. Do not change to a 4.10!!! Diesel engines are not designed for high RPMs I have 3 2004 dodges trucks, love the 5.9. Leave the rear alone and upgrade your transmission, take a look at FirePunk. There are others that are really good too. The best combo for the 5.9 is the 6 speed manual, auto has many issues and TC does not lockup very well. Get the advice of people that rebuild these 5.9s.

[Campy]

To the OP, how does the truck drive now? Changing gear ratio is a viable option depending on how the truck likes to perform. My 08 Duramax likes to pull at 2100-2200 rpms and will drag my camper with ease. Now the problem is with the 3.73 axle ratio it has the "normal" operating RPM's are 1800-1900 so the truck would really like a slightly higher RPM for dragging the load. I have asked around to see if simply going to a smaller tire diameter would get me the RPM's but it does not seem to add up. I have been considering a gear ratio change but the 4x4 thing is costly for the gears and install sets, I can do the work myself. I have a 6 speed Allison trans but have to manually limit it to 5 gears to get the performance the truck is looking for.

[chuckster57]

NOOO!!!! No. Do not change to a 4.10!!! Diesel engines are not designed for high RPMs I have 3 2004 dodges trucks, love the 5.9. Leave the rear alone and upgrade your transmission, take a look at FirePunk. There are others that are really good too. The best combo for the 5.9 is the 6 speed manual, auto has many issues and TC does not lockup very well. Get the advice of people that rebuild these 5.9s.

My truck came with 4:10 rear end. I have pulled my current and old fifth wheel up some very steep grades and ran it at 2600-2800 rpms with no issues. It’s actually better for a turbocharged Diesel to pull at higher RPMs since it keeps the turbo spooled up to max boost and moves air in/out of the engine. Gas engines have a higher rev limit.

[rickhz]

4:10 is actually a higher ratio.

Hate to argue with the boss, but...

Higher in numbers, lower ratio.

Tall (high) gears have LOWER numerical numbers such as 2.79, 2.90, 3.00, 3.25. ... If you are cruising down the freeway at 60 MPH with 3.00 gears, in a typical high gear with a 1:1 output ratio, it simply means that the drive shaft (engine) is spinning 3 times for every 1 rotation of your tire.

------------------

A lower (numerically higher) gear ratio, such as 3.55:1 to 4.10:1, provides more low-speed wheel torque, which means it takes less throttle to get the vehicle and the load it’s carrying or towing moving.

https://www.hardworkingtrucks.com/understanding-axle-ratios/

[kf4wsn]

Look At any Vehicle Spec and you will see that lowering the gear Ratio is the best way to increase tow capacity. Most people assume that it is mostly from increasing engine size only. The 4:10 is an Awesome Ratio for towing and makes it a breeze to pull. A Big killer is when people have to High a ratio like 3:73 and then add Taller tires and that makes the ratio even higher. I think that you will be most impressed with the added pulling power as well as the extra engine breaking. I don't think the dealers like to order trucks with the low ratios I had to special order mine and they would much rather sell one that is in stock or close by. But if you tow or Off road they are well worth the wait

[Javi]

Personally with most of today's auto transmission gear ratios/over drive the 4:10 has become pretty much unnecessary unless towing heavy (14K and up) full time.. My older Ram with the 5.9 two valve and the 5 speed manual needed 4:10's to untrack itself with 14K :D

My current dually with the 6.7 Ford and 3:73 ratio is plenty for anything less than heavy daily towing...

[travelin texans]

Duramax with 6 speed Allison in tow/haul mode with exhaust brake enabled mated to 3.73 rear end will tow 16.5k 5er ALL day long at 65-68 mph/1700 rpm with cruise set up or downhill getting 10 mpg & never breathe hard.

[BOU0146]

I have a 2009 Ram 3500 Megacab dually 6.7L with a 3.73 rear end. I pull a 17000lb. Montana 3810MS and am very happy with the way it handles it.

[66joej]

I have a 2009 Ram 3500 Megacab dually 6.7L with a 3.73 rear end. I pull a 17000lb. Montana 3810MS and am very happy with the way it handles it.

Yes but you are in Saskatchewan. I think a 1/2 ton would handle that puppy.:hide::lol:

[cookinwitdiesel]

Another vote for upgrades being a money pit. If you can manage it, a newer vehicle will bring a lot of the upgrades you are looking for and many you aren't as well (quality of life stuff). A quick check on Carmax shows a lot of 3500 Diesel Rams around the country with very low mileage (for a Diesel and what it is made for). There are of course other brands too but since we were talking about a Ram, figured I would stick to that.

[Tinner12002]

On a later model Ram dually with the 6.7 the towing difference between 3.73s and 4.10s without the Aisin and HO motor is about 3000lbs, with the Aisin and HO motor there is a 6000lb difference so there is obviously more than just gear ratio involved. I had to look at the dually as those ratios aren't available on the SRW. The OP has an older 5.9 so I'm guessing the difference would be a lot less. Plus the auto trans in those models is a weak link also. Personally, I'd maybe look for a later model Ram with the bigger motor though I realize that may not be an option.

[fourfourto]

:popcorn: H3 has 4.56 gears 4 to 1 low granny gear :cool: but a 5 cyl 4500 lbs tow :ermm::lol:

[sourdough]

:popcorn: H3 has 4.56 gears 4 to 1 low granny gear :cool: but a 5 cyl 4500 lbs tow :ermm::lol:


442- Had a 2006 H3 with the 5 cylinder until 2010. They had great ratios for 4 wheeling but just didn't have enough power to get down the hiway at any speed, much less tow anything more. Ran the H3 from NV, AZ, TX, NM, CO, OK, WY, LA, GA, MS, GA, FL, NC, SC and more. I loved that H3 for off roading; I've not had a regular size SUV that could actually go over Elwood Pass without using some sort of traction lock or 4 low; the H3 did the whole thing and I never pulled it out of 4 Hi....I was impressed. Anyway, the H3 was a great off road vehicle to me but I just could never think of strapping anything of any size behind it....JMO YMMV.

[fourfourto]

That's why I have a light weight camper,3200 dry 4000 max heavy.
Except for the long hills were it wants to go to 2nd gear at 60 mph I just slow it down to 50 maybe 45 for the steep long hills.
The hills in ny are not a problem 50 to 55

[moodman]

Personally with most of today's auto transmission gear ratios/over drive the 4:10 has become pretty much unnecessary unless towing heavy (14K and up) full time.. My older Ram with the 5.9 two valve and the 5 speed manual needed 4:10's to untrack itself with 14K :D

My current dually with the 6.7 Ford and 3:73 ratio is plenty for anything less than heavy daily towing...

I'm curious. You said "older RAM" and then you said it needed 4:10 to untrack itself.

First, what year was your older RAM, and second, what did you mean "untrack itself"?

[Snoking]

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.

The swap should be the whole truck for a 2013 or newer 3500 SRW with Aisin. Spending big bucks on a 2003 is not the best plan.

Our 2001.5 with 4.10's towed well. The choice then was 3.54 or 4.10. Your 3.73 are a compromise between the two. If you had 3.54's then you would see a pretty good change, however with 3.73's, the change would not be worth the cost. It would cost north of 10k to put a Aisin in, and i am not sure anyone has worked out now to shift it.

We love our 2015 3500 SRW Aisin setup. Tow a 16K 39.5' 5er. Chris

[Javi]

I'm curious. You said "older RAM" and then you said it needed 4:10 to untrack itself.

First, what year was your older RAM, and second, what did you mean "untrack itself"?'94

Untrack... getting 14K up to highway speeds quickly enough to avoid traffic accidents when entering two lane roads..