Changing differential gears

[delwhjr]

WWould like to hear from those that have actually changed their rear-end ratios.
Did you get any improvement?
Was it worth it?
Any pitfalls?

[Huntindog]

Same color

[BenK]

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

[Huntindog]

I have a 73 Blazer that I bought in 85. It had 3.73s. That reved pretty good with stock tires and the TH350. When the tranny went, I installed a TH700R4. A lower 1st gear, and an overdrive made this a great choice. It was my first TV. Then one of the front springs broke while I was towing. Made it home fine with it that way only discovering it when backing into the drive. Priced new stock springs....Ouch.
So ended up with all new 2.5" lift springs/shocks for a lot less $$$. Then the stock tires looked silly, so at new tire time, 32"s went on. Then the OD was too steep. Mileage went down a lot and OD wasn't much use. When it was axle rebuild time, I installed 4.10s front and rear with a Trutrac in the rear and an Auburn in the front. I did it myself.
Cost wasn't bad at all. It did take some time and a few new tools.

What a difference! Mileage improved by 29%!!
power was better in every gear.

So yes, if your present gears are not working for your situation.... Getting the right ones for the job will make a world of difference, and very well may improve economy as well.

I am positive that my initial cost has been returned and then some, over the last 10 years in fuel savings. The better drivability is a bonus.

[time2roll]

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.

[delwhjr]

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.

[parker_rowe]

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.

[EnzoColorado]

I changed my Suburban's 3.08 to 4.10 and it's like having a new engine in there, much improved drivability towing or empty.

[valhalla360]

ScottG wrote:

I understand what your saying and I believe Ram's specs but if you talk to people who have gone from 3.42 SRW's and moved up to a dually with 4.10's, the driving experience is vastly improved even when not loaded. When loaded they're able to get off the line much better which is always a sore point with diesels. I'm hoping the fifth gens have an 8 speed trans to make the 3.42's more palatable (doubtful).

Of course that will do better off the line towing heavy, you are looking at 20% more torque going to the wheels with that change assuming everything else is unchanged.

Define "driving experience". If you are willing to give up some MPG, it will be faster accelerating running empty but really, modern diesel trucks are not hurting for power running empty. They have plenty good acceleration. But most people would prefer a couple extra MPG if they do any significant driving not towing.

[ppine]

It costs a lot. The best solution is a lighter trailer.

[Cummins12V98]

"I understand what your saying and I believe Ram's specs but if you talk to people who have gone from 3.42 SRW's and moved up to a dually with 4.10's, the driving experience is vastly improved even when not loaded. When loaded they're able to get off the line much better which is always a sore point with diesels."

Completely disagree with being "Vastly improved", sure the 4.10 takes off easier but unloaded I wish I could lock out first gear as you get rolling and it hits second.

The AISIN is key to making the 3.42's work well towing HEAVY. My Son has a 15 Limited 3500 4x4 SRW AISIN. I have towed his 14k dump trailer at a combined of around 26-27k, took off on a good grade with ease. My 11 HO Dually same gears on grade struggled at 28k. If the AISIN were in that truck I would be still towing with it even at my 33-35k loads.

Bottom line 3.42's/AISIN can't be beat for performance and fuel economy BOTH up to 29K+ !!!

If I get a 19 or 20 even at 35K I will most likely buy the 3.42's this time over the 4.10's. WITH THE AISIN!

Ask MeAgain of his 3.42/AISIN towing experiences.

[ScottG]

valhalla360 wrote:

ScottG wrote:
It looks like our next RAM 3500 SRW will have to have 3.42 diff (unless they change for 2020 with gen 5) so it is entirely possible I will have them changed out for 3.73 or even 4.10 within a couple of years.

You are thinking of the old days with 3 speed automatics when you couldn't get a gear ratio that did what you wanted and the only way to make up for it was a deeper rear end at the sacrafice of MPG when running empty. With modern 6-10speed automatics, they are much better able to keep engine operating in it's ideal HP/Torque range.

It's important to look at the overall gear ratio (between the crank shaft of the engine and the rubber on the road).

To the OP: Take the new ratio and divide by the old ratio. That will give you a rough estimate of what percentage of pulling power increase you can expect. Speed up steep grades will still be limited by HP but if you are not making it up hills or struggling, it will do better relative to the change in ratio.

I understand what your saying and I believe Ram's specs but if you talk to people who have gone from 3.42 SRW's and moved up to a dually with 4.10's, the driving experience is vastly improved even when not loaded. When loaded they're able to get off the line much better which is always a sore point with diesels. I'm hoping the fifth gens have an 8 speed trans to make the 3.42's more palatable (doubtful).

[valhalla360]

ScottG wrote:
It looks like our next RAM 3500 SRW will have to have 3.42 diff (unless they change for 2020 with gen 5) so it is entirely possible I will have them changed out for 3.73 or even 4.10 within a couple of years.

You are thinking of the old days with 3 speed automatics when you couldn't get a gear ratio that did what you wanted and the only way to make up for it was a deeper rear end at the sacrafice of MPG when running empty. With modern 6-10speed automatics, they are much better able to keep engine operating in it's ideal HP/Torque range.

It's important to look at the overall gear ratio (between the crank shaft of the engine and the rubber on the road).

To the OP: Take the new ratio and divide by the old ratio. That will give you a rough estimate of what percentage of pulling power increase you can expect. Speed up steep grades will still be limited by HP but if you are not making it up hills or struggling, it will do better relative to the change in ratio.

[memtb]

Oh, for the days of the 9” Ford Differential....a couple of hours in the driveway , a chunk change-out (purchased at the local wrecking yard)....and drive away with the ratio of your choice!

[APT]

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.

[Cummins12V98]

ScottG wrote:
It looks like our next RAM 3500 SRW will have to have 3.42 diff (unless they change for 2020 with gen 5) so it is entirely possible I will have them changed out for 3.73 or even 4.10 within a couple of years.

With the AISIN the 3.42's are good to over 29k combined SAE rated.

Change gears and you go from 100k coverage to 12k or one year.