Changing differential gears

mtofell1 wrote:

ol' yeller wrote:
Gas mileage didn't improve or degrade enough to notice.

I think this is what a lot of people need to read and reread. Whenever gearing discussions come up, the whole MPG thing is way overstated. Unless you are doing a very drastic change it likely won't be noticed.

Just to throw some real numbers out there.
With my 3.73 to 4.30 swap I gained .5 mpg towing and the same amount in city/hwy driving. I did lose that .5 mpg on the hwy with no trailer, but when you go from 14.8 to 14.3 its not a dealer breaker! and the X very rarely doesn't have the trailer attached to it.

And when I added the tuner from 5 star tuning a year later it really woke up the V-10! it shifted the way it should have from the factory! Fords shift strategy leaves a lot to be desired. and here again because of its ability to hold each gear longer when upshifting (which uses the available power more efficiently, meaning no short shifting) and its ability to hold OD a bit longer reducing downshifting, I gained another .3 mpg. yes these are real world numbers and not something I dreamed up.
And every time I see the RPM drop on the 1-2 and 2-3 shift it makes me sick, that's how terrible it is at transferring power!

One final thing I did was add an air deflector to push the air up and over the trailer. and this again gave me another .4-.5 mpg. So When I started out I was getting around 6.3 with my V-10. I can now get 7.5-7.7 all day. if its not windy and I slow down I get 8, although that is very rare that's its not practical to go by.

Now with all that said. the newer 6,8,9 and 10 speed transmission are very efficient at transferring power. so unless your towing really heavy you are not going to see much of a change.

ol' yeller wrote:
Gas mileage didn't improve or degrade enough to notice.

I think this is what a lot of people need to read and reread. Whenever gearing discussions come up, the whole MPG thing is way overstated. Unless you are doing a very drastic change it likely won't be noticed.

My experience was with a '99 Ford Superduty F250 with a V10 Supercab, 2WD. I changed out the 373 gears for 430's several years ago. We were towing a bumper pull that weighed around 7,500# loaded. Before the change, the engine would constantly downshift at even the slightest hill or need for acceleration. After the change the engine stayed longer in its sweet spot without dropping a gear so easily. It was expensive even for 2WD but I also added limited slip and it was like an entirely different truck handling wise. Probably not a great investment financially but for the grins, it was well worth it. Did I mention how much better the truck stepped out from a stop as well? Gas mileage didn't improve or degrade enough to notice.

What part of Texas do you live in?

A lot of the bigger towns have 4x4 shops. Might be worth checking with them. Years ago, I had a Toyota 4x4 that I went with bigger tires on. I did the work myself to remove the axles and pumpkin (wasn't really that hard), bought the parts and they put then in the pumpkin and shimmed it for about $100. Probably more now.

Company is 4 wheel parts and they have stores in DFW, Austin, San Antonio, Houston, Beaumont and McAllen. Any good axle shop should be able to easily do the work.

Geese...memories of my 1973 !!!

Dana 60 front, GM 14 bolt rear end.4.1’s, new-positive arched front leaf springs, 33/12.5x16.5 load range F, 45 gallon main tank, 2” dia full roll cage from windshield to rear wheel wells, Audi 5000 front buckets, etc etc



To the OP... for each GM change in diff ratio...begets approx 10% change in torque multiplication. Example...go two higher numeric...approx 20% more torque to the axles

So, I’d change them...some times...gain a bit more MPG while towing heavy, as the engine doesn’t work as hard

Real benefit if you feel you can't use all the gears much when towing. My truck has an old 4 speed (4R70W) and would barely hold 3rd when towing so basically I had a 2 speed trans. After swapping 3.55 to 4.10 I easily hold 3rd gear and can periodically cruise in 4th (OD). Less effect if you have a newer 5 or 7+ speed transmission. Still if you can only use half the gears it is time for the differential to change.

APT wrote:
Many people change gears to a numerically higher. I generally recommend changing at least two steps. So 3.55->4.10+ is beneficial. 3.55->3.92 is not (enough). Almost always with respect to towing, people are more pleased with the performance afterwards. Better acceleration, same to better fuel efficiency in city and towing.

Pitfalls: unloaded highway fuel efficiency and engine speeds. Costs. From an asset investment point of view, you will never get back what you spend. It will be $500-1500 per axle plus a tuner to change the transmission shift patterns. This could be a large amount of money on a 12+ year old vehicle.

As mentioned, selling the current vehicle and spending the extra $3k on a different more capable vehicle is generally a better $ investment. Full sized SUVs with much better geared 6-spd transmissions started in 2007 with Toyoda Sequoia and Ford Expeditions and 2009 GM twins.

However, if you really love your Durango, it is well maintained, it is a recreational/towing vehicle only and you can afford it, then I'm sure you will notice and enjoy the increased acceleration from stopped and better throttle response.

Thank you
This is what I was looking for. The change out is partly DIY with a friend. The numbers on the truck and trailer combo are good with everything falling below stickers (CAT weighed). Was just trying to validate possible benefits.

I have 4.56's going in soon, can't wait. Probably a little steep for most people, but I've ran the numbers and know what I'm getting into. In the mail as we speak.

Gears make a difference towing for sure. Sometimes you can get increased towing and around town mileage, but I wouldn't count on that. Most gas engine tow packages include steeper gears for a reason.

I only use my Suburban for towing and Lowe's runs so I'm really looking forward to it.