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Changing differential gears

delwhjr
Explorer
Explorer
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?
2022 Rockwood 2109S
2006 Durango HEMI
38 REPLIES 38

Huntindog
Explorer
Explorer
Same color
Huntindog
100% boondocking
2021 Grand Design Momentum 398M
2 bathrooms, no waiting
104 gal grey, 104 black,158 fresh
FullBodyPaint, 3,8Kaxles, DiscBrakes
17.5LRH commercial tires
1860watts solar,800 AH Battleborn batterys
2020 Silverado HighCountry CC DA 4X4 DRW

BenK
Explorer
Explorer
Geese...memories of my 1973 !!!

Dana 60 front, GM 14 bolt rear end.4.1โ€™s, new-positive arched front leaf springs, 33/12.5x16.5 load range F, 45 gallon main tank, 2โ€ 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, Iโ€™d change them...some times...gain a bit more MPG while towing heavy, as the engine doesnโ€™t work as hard
-Ben Picture of my rig
1996 GMC SLT Suburban 3/4 ton K3500/7.4L/4:1/+150Kmiles orig owner...
1980 Chevy Silverado C10/long bed/"BUILT" 5.7L/3:73/1 ton helper springs/+329Kmiles, bought it from dad...
1998 Mazda B2500 (1/2 ton) pickup, 2nd owner...
Praise Dyno Brake equiped and all have "nose bleed" braking!
Previous trucks/offroaders: 40's Jeep restored in mid 60's / 69 DuneBuggy (approx +1K lb: VW pan/200hpCorvair: eng, cam, dual carb'w velocity stacks'n 18" runners, 4spd transaxle) made myself from ground up / 1970 Toyota FJ40 / 1973 K5 Blazer (2dr Tahoe, 1 ton axles front/rear, +255K miles when sold it)...
Sold the boat (looking for another): Trophy with twin 150's...
51 cylinders in household, what's yours?...

Huntindog
Explorer
Explorer
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.
Huntindog
100% boondocking
2021 Grand Design Momentum 398M
2 bathrooms, no waiting
104 gal grey, 104 black,158 fresh
FullBodyPaint, 3,8Kaxles, DiscBrakes
17.5LRH commercial tires
1860watts solar,800 AH Battleborn batterys
2020 Silverado HighCountry CC DA 4X4 DRW

time2roll
Nomad
Nomad
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
Explorer
Explorer
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.
2022 Rockwood 2109S
2006 Durango HEMI

parker_rowe
Explorer
Explorer
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.
2015 Starcraft TravelStar 239TBS 6500 GVWR
1997 GMC Suburban K2500 7.4 Vortec/4.10
1977 Kawasaki KZ1000

EnzoColorado
Explorer II
Explorer II
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.
2017 Starcraft AR-ONE MAXX 20BHLE
2012 Suburban 2500 LT 4WD

valhalla360
Nomad III
Nomad III
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.
Tammy & Mike
Ford F250 V10
2021 Gray Wolf
Gemini Catamaran 34'
Full Time spliting time between boat and RV

ppine
Explorer II
Explorer II
It costs a lot. The best solution is a lighter trailer.

Cummins12V98
Explorer III
Explorer III
"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.
2015 RAM LongHorn 3500 Dually CrewCab 4X4 CUMMINS/AISIN RearAir 385HP/865TQ 4:10's
37,800# GCVWR "Towing Beast"

"HeavyWeight" B&W RVK3600

2016 MobileSuites 39TKSB3 highly "Elited" In the stable

2007.5 Mobile Suites 36 SB3 29,000# Combined SOLD

ScottG
Nomad
Nomad
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
Nomad III
Nomad III
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.
Tammy & Mike
Ford F250 V10
2021 Gray Wolf
Gemini Catamaran 34'
Full Time spliting time between boat and RV

memtb
Explorer
Explorer
Oh, for the days of the 9โ€ 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!
Todd & Marianne
Miniature Schnauzer's - Sundai, Nellie & Maggie Mae
2007 Dodge Ram 3500, 6.7 Cummins, 6 speed manual, 3.73 ratio, 4x4
2004 Teton Grand Freedom, 39'
2007 Bigfoot 30MH26Sl

APT
Explorer
Explorer
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.
A & A parents of DD 2005, DS1 2007, DS2 2009
2011 Suburban 2500 6.0L 3.73 pulling 2011 Heartland North Trail 28BRS
2017 Subaru Outback 3.6R
2x 2023 Chevrolet Bolt EUV (Gray and Black Twins)

Cummins12V98
Explorer III
Explorer III
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.
2015 RAM LongHorn 3500 Dually CrewCab 4X4 CUMMINS/AISIN RearAir 385HP/865TQ 4:10's
37,800# GCVWR "Towing Beast"

"HeavyWeight" B&W RVK3600

2016 MobileSuites 39TKSB3 highly "Elited" In the stable

2007.5 Mobile Suites 36 SB3 29,000# Combined SOLD