To change differential or get a US Gears?

[ReggieRam]

OK, so I'm a little bent here. My buddy just got a new 2002 2500 4x4, automatic with 3. 54's, and he got 18. 5 MPG out of his first tank of fuel! That's the best I've ever gotten out of my 3500 4x with the 4. 10's, so I got to thinking. How difficult/expensive would it be to change over to 3. 54's front and rear, and how disappointed would I be at the lost power? At present, I'm not a really heavy tower, but I have been eyeballing a 30' fishing boat for future reference.



The other option is to go with a US Gears overdrive to get the best of both worlds. The deciding factor isn't necessarily cost, but it is a factor. Can anyone give me an approxiamte cost of doing either or both? Thanks in advance for the help.

 

[Neibe]

You have a heavier truck 3500versus2500 I'd be happy with 18. 5mpg with 4. 10 gears. I get 17-19 with mine.

 

[brobeson]

4.10 or 3.55

Over the years there have been independant tests using the exact same vehicles, running on the same road course to test the MPG differances between the higher or lower gear ratios and how they effect MPG.



There has never been a big enough differance between the 2 to notice a MPG differance.



The differance would be in the number of RPM's over the life of the enigine and how offen you need to down shift on hills etc.



Running empty get 3. 55s, towing anythning above about 7000 lbs, get the 4. 10s.



There are way to many other things that effect MPG than the gear ratios at normal speeds.





Bob

 

[Reddog1]

Bob is on track. I have the U. S. Gears (as an underdrive), with 3. 5s and 2WD. As I recall, 1500 RPM @55 in direct and 2100 RPM @ 55 in underdrive. I am still doing test. Consider the following:



1. Automatic 2500 Ram empty (weight = 6200 lbs).

2. In hills, from 200 feet to 1600 feet elevation, four stop signs, 54 miles round trip.

3. Gear charts indicate 3. 5 gears in direct, and 4. 1s in underdrive.

4. 19 MPG in direct and 18 MPG in underdrive.

5. The original owner of my Ram Paid about $2900 for the U. S. Gear Transmission, plus driveline and Installation.

6. Definitely more power in underdrive, but lower top speed.



Conclusion, you can buy a lot of fuel for $3000 plus, if power is your objective.



I am led to believe timing has a lot of influence on fuel economy.



Wayne

 

[ReggieRam]

Reddog-



That answer is pure Zen! Not like I drive that fast anyways.

 

[klenger]

I've got the 4. 10's on my 2500 and really like it, ... alot more than I thought I would. I rarely drive over 65 MPH, so they work out well.



Assuming that the 4. 10's got 18 MPG and the 3. 54's got 19 MPG (1 MPG diff), you would need to drive the truck 682,000 miles to save the $3000 investment assuming fuel at $1. 50 / gal. If the milage difference is actually greater, that would cut down the payback time, and cheaper fuel would increase the payback time. Of course, the underdrive/overdrive could fail and need to be repaired sometime during the 682,000 miles.



Personally, I'll just accept the better performance with the 4. 10's and keep the money. It seems that this logic is even stronger for the 3500.



Good luck

 

[Boost]

I recently traded a 01 with 4. 10 for a 01 with 3. 55. The main reason I traded was to go from a 5sp to a 6sp, but secondary was to get the 3. 55's. And now the only thing I would change on my new truck would be the 3. 55's. My 31ft 5ver weighed 12,600 the last time I weighed it and the 4. 10's just plain worked better for that weight. On the other hand I tow a smaller 7500# trailer most of the time and there is little difference between the ratios at that weight. Mileage is about 1. 5 mpg better with the 3. 55's empty or loaded.



Rob

 

[jmeehan]

You could always go with a taller tire. I like the look of the Rickson wheels on the 3500's, and with the right aspect ratio tire you could get your final drive down to around 3. 73's.

 

[pwr2tow]

ReggieRam, The dealer quoted me $2,600 to change gear ratio. The reason is with the dana 80 rear you have to change the carrier. I would be more than happy to change ratios with you as I pull heavy and need the extra grunt of the 4:10's. The problem is i never travel very far east of ND. If i were you I would keep those gears and when you get that boat have your friend pull it and he will wish he had the 4:10's.



Ron

 

[Reddog1]

No one commented on: “I am led to believe timing has a lot of influence on fuel economy. ” I am kinda new at this, let’s have a response . Agree or disagree?





Wayne

 

[inwards]

Reggie I had the us gear overdrive put in my truck by camping world. They did a nice job and install is guaranteed forever. (labor that is) I pull a 37 ft 5ver and sure like it. Have had it about 2 years now and no trouble. It is a well built unit.

 

[Randy J]

I to would be willing to change gear sets with you. I have the 3:55's in my 98. 5. With the 285 tires I have, I'd kind of like to have 4:10 gears.

 

[RobG]

Before you spend the money on a gear change or an overdrive/underdrive, try this:



- Get the DTT automatic

- Up your power a bit (say, DD1's and a DD TTPM or Edge EZ)

- Guages (of course)



Try it like that for a while and see how you like it. If it still feels lacking, then consider the overdrive box (configured as an underdrive.



I don't think you'll need it unless you tow a LOT of weight very frequently. The torque multiplication of the automatic and the extra power should make life super simple for you, and the mods should keep your EGTs down enough (especially if you swap to an HX-35) so you don't have to watch the guage all the time.



That's my two cents' anyway.



Rob

 

[Reddog1]

I find many of the post lacking. To assist someone in making a decision which may cost several thousand dollars, it would be helpful in knowing why we believe a product is or is not of value. Supporting data would be great. I do not mean to be rude, but faith alone does not make a product good or bad.



I agree with ROB. I suggest you spend your money on the changes he suggests.



I have the U. S. Gear Transmission. It was installed by Camping World. I have no complaints with either. However, I do think from my experience so far, that the other mods would have been a better investment.



Wayne

 

[RAMalama]

My 95 was the same as my signature. The 12v motors are easier to figure out how to run for efficiency cause they do not constantly moniter and change fuel timing. These 24v adjust themselves to what ever speed you set your cruise to. My 24 gives me 17-19 tank after tank.



I don't think the US Gear unit will give you the difference in mileage you're looking for. Just the same though, I'm still looking for "7th" gear just as I looked for "6th" in my 95 five spd...



My . 02