Diff gearing change advice please

[Armando Sgroi]

Towing a 4000kg Caravan and looking to strengthen transmission and get a tune - 2018 2500 ( heavy due to mods and running 37s) - would you recommend a change to 4.3 diff gearing? - and what parts supplier should I use?


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[NJMOPAR]

Have to change front and rear to match.
Many thousands of dollars is the start.

 

[62Blazer]

What gearing does it currently have? Typically 3.73 or 4.10.

Assuming you have 3.73 gears stock then running through a gear calculator states 4.30 gears are needed to compensate for 37" tires. Keep in mind that is only for the increased diameter and does not account the increased rolling mass and road resistance typically associated with larger tires. You also mention the overall truck is heavier than stock because of mods. Also note that just because a gear calculator states a certain ratio it doesn't mean that ratio is even available.

If you have the factory option 4.10 gears than the calculator states 4.74 gears (actually available are typically 4.88).

Overall, between 37" tires, increased truck weight because of mods, and towing a 9,000 lb. trailer I would lean towards a 4.88 gear and possibly even 5.13.

 

[BOWERSFJ]

Towing a 4000kg Caravan and looking to strengthen transmission and get a tune - 2018 2500 ( heavy due to mods and running 37s) - would you recommend a change to 4.3 diff gearing? - and what parts supplier should I use?


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Start with 2WD OR 4WD ? And what gears you have now ?


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[Armando Sgroi]

Start with 2WD OR 4WD ? And what gears you have now ?


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4WD and stock gears on 2018 Laramie 2500 which I thought were only 3.73 how do I tell?


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[Armando Sgroi]

Start with 2WD OR 4WD ? And what gears you have now ?


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I looked here https://www.dodge.com/webselfservice/BuildSheetServlet?vin=

and entered my VIN number and the data sheet says I only have a 3.42 Axle ratio !!!

 

[BOWERSFJ]

Well to start, 4WD means both axles ... Gonna cost a bunch of money ... Don’t know much about aftermarket gears ... Lotta good ones ... But you for sure could put OE 4.10 gears in there for a huge improvement


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[RLJ10X]

37s, with 3.42s...... ugh!

You might want to do 4.56s.

Is the front carrier on the 2500 welded like the 1500s?

 

[crash68]

entered my VIN number and the data sheet says I only have a 3.42 Axle ratio !!!

3.42 was the only gearing on the 2500 with the Cummins engine.

37s, with 3.42s...... ugh!

You might want to do 4.56s.

Is the front carrier on the 2500 welded like the 1500s?

Being his truck is a CTD, you don't need to go nearly as low with the differential gearing. If you go to low you'll run out of rpms in the motor for driving down the road, the Cummins has gobs of torque to turn the wheels. He's probably good with 4.10 with the 37s on the truck, it will be slightly under the factory gearing with stock tires.
The bigger issue will be building up the RFE68 transmission to handle the HP/torque as he looking to tune

The front carrier is not welded on the 2500s like the 1500s, it also has a solid front axle.

 

[Armando Sgroi]

3.42 was the only gearing on the 2500 with the Cummins engine.



Being his truck is a CTD, you don't need to go nearly as low with the differential gearing. If you go to low you'll run out of rpms in the motor for driving down the road, the Cummins has gobs of torque to turn the wheels. He's probably good with 4.10 with the 37s on the truck, it will be slightly under the factory gearing with stock tires.
The bigger issue will be building up the RFE68 transmission to handle the HP/torque as he looking to tune

The front carrier is not welded on the 2500s like the 1500s, it also has a solid front axle.

Thanks - yes also plan on building up the transmission - looking at all the options from Sonnax


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[Elkman]

Check the Ram tow rating for your truck with its engine and the 3.42 gears and if it is greater than 4000 kilos then I would forget about it. More important is the transmission fluid cooler for the truck and aftermarket ones are not at all expensive.

 

[crash68]

Check the Ram tow rating for your truck with its engine and the 3.42 gears and if it is greater than 4000 kilos then I would forget about it.

I sure hope the Cummins(it's the only Ram truck engine that uses 3.42) can tow 4000kg, considering it's 1500 counter part EcoDiesel can. A CTD can tow double what he's looking to tow

 

[Armando Sgroi]

I sure hope the Cummins(it's the only Ram truck engine that uses 3.42) can tow 4000kg, considering it's 1500 counter part EcoDiesel can. A CTD can tow double what he's looking to tow

Yes GCM is about 8500kg but with the heavy truck and 37s just looking to protect the 68RFE - sounds like a 4.1 or 4.3 gear ratio makes sense combined with transmission strengthening before we apply a tune

Cheers


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[RLJ10X]

Cummins.

my bad.

you’re right. I’m wrong.

 

[RamminMopar]

There's also 4.30. gears

 

[62Blazer]

3.42 was the only gearing on the 2500 with the Cummins engine.



Being his truck is a CTD, you don't need to go nearly as low with the differential gearing. If you go to low you'll run out of rpms in the motor for driving down the road, the Cummins has gobs of torque to turn the wheels. He's probably good with 4.10 with the 37s on the truck, it will be slightly under the factory gearing with stock tires.
The bigger issue will be building up the RFE68 transmission to handle the HP/torque as he looking to tune

The front carrier is not welded on the 2500s like the 1500s, it also has a solid front axle.

I was originally thinking 6.4 gas in regards to 3.73 or 4.10. I agree with the above as 4.10's will put you back close to stock RPM's with the 37's.