6.4 Hemi Gear Swap

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mtofell

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This is just a fleeting thought at this point but I'm curious what is even available. In searching the forum all I can find is info on 1500 trucks.

I have a 2500 gas with the 3.73s and I know the 4.10s were an option. Are there 4.30s and/or 4.56s (or something else?) available for my truck? It's a 4X4 so I'll need both front and rear.
 

brandonjansen

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4.10's or 4.56's yes. 4.30's are for the rear diff but next to impossible to find for the front diff.

You'll need ring and pinion kits and pinion install kits at a minimum. Likely pinion bears as well as they are generally destroyed trying to remove them from the stock pinion.

What exactly is your reasoning for wanting lower gears? Planning to be running 37's?
 

spiG

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Somebody on here has already done the swap but can't remember who. I'm sure they will chime in soon.
 

Ratket

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Karl45- I believe is his name, he had a dealer install 456- and twilliams had a shop he knows install his 456. Karl"s are covered under his warranty since he had the dealer do it, but it cost him almost 3X what twilliams cost to do his. This is a mod I really want to do. I think it is the perfect gear match for these trucks with a 35" tire. or even if u stay stock size and tow regularly.
 
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brandonjansen

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Somebody on here has already done the swap but can't remember who. I'm sure they will chime in soon.

..... I have.... Mine's a 2012 3500 Cummins however the front differential is the same between the two (9.25 AAM) and the rear differential is very similar. 10.5" AAM on the Hemi 2500's VS an 11.5" AAM in my Cummins. The design is the same between the two.
 
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mtofell

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What exactly is your reasoning for wanting lower gears? Planning to be running 37's?

No change in tire size.... just looking at towing heavy. I wish I'd have held out for the 4.10s but they are/were hard to find so I just took what I could get. The change to 4.10 gives another 3000# in towing capacity. If swapping to 4.10 is easiest/cheapest I'd likely go that route. I was just thinking as long as I were doing it I might as well see if going up a couple steps made sense. Also, gas is on my company so MPGs really don't matter to me.... within some reason.

Realistically, I'm not looking at towing super heavy and I'll most likely just stick with what I have. I'm somewhat kicking myself for not just getting a diesel but that's just life. I'm not minding having the extra 6K in my pocket now that I would have spent. Overall, I love the Hemi and am pleased with the way it tows. I'm just a weekend RVer and 95% of my miles are spent with no trailer so it's not a huge deal.

If I could jump up to the 4.10s for less than a couple thousand dollars and keep my warranty all intact (so, work done at the dealer I suppose) I'd probably go for it. Otherwise, it's not like I'm in terrible shape with the truck I have.
 

Ratket

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How quick is that cummins to smoke those 37"s through that 456 gear set?
 

Ratket

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456"s at a shop is like 1600$ I think..well worth it, u should get better mileage on the why as mds will activate easier.
 
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brandonjansen

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No change in tire size.... just looking at towing heavy. I wish I'd have held out for the 4.10s but they are/were hard to find so I just took what I could get. The change to 4.10 gives another 3000# in towing capacity. If swapping to 4.10 is easiest/cheapest I'd likely go that route. I was just thinking as long as I were doing it I might as well see if going up a couple steps made sense. Also, gas is on my company so MPGs really don't matter to me.... within some reason.

Realistically, I'm not looking at towing super heavy and I'll most likely just stick with what I have. I'm somewhat kicking myself for not just getting a diesel but that's just life. I'm not minding having the extra 6K in my pocket now that I would have spent. Overall, I love the Hemi and am pleased with the way it tows. I'm just a weekend RVer and 95% of my miles are spent with no trailer so it's not a huge deal.

If I could jump up to the 4.10s for less than a couple thousand dollars and keep my warranty all intact (so, work done at the dealer I suppose) I'd probably go for it. Otherwise, it's not like I'm in terrible shape with the truck I have.

If you're sticking with stock tires I wouldn't go any lower than 4.10's. That will already be pretty low for those tires. If you ever plan on going to 35's or something then 4.56's may be a good option.

The price to have 4.10's or 4.56's installed will pretty much be the same. The parts will be very similarly priced; it's the labor that's the expensive part. I paid just shy of $3000 for my 4.56's installed including all parts, labor, sythetic oil (which was a lot in my truck with the Mag-Hytec rear diff cover), and tax. I had a few quotes from US shops to do it as well and they were in the $2300 range I believe. So I'd say that's roughly what you're looking at if you have a shop do it. For a dealership to do it I'd imagine you're look at a lot more if they even know how to do it. Honestly I wouldn't ever have a dealership touch a differential on my truck. They're something that needs to be setup right the first time or you will chew up the gears. Having an experienced driveline shop complete the work will be worth it.

You shouldn't have any issues with warranty doing that. For one, the dealership will never even know you changed them. Two, they would have to prove the gears are the cause of the problem if something ever did happen which simply won't be the case. 4.10's will make it easier on your driveline, not harder.

For the record, even if you do change your gears your truck doesn't legally have a higher towing capacity. Any authority will still go off what the door sticker says which is what the truck is rated at with 3.73's. Sure it will tow much better and common sense would tell you that it should be able to legally tow more. But unfortunately insurance companies and a lot of authority lacks common sense. That's only applicable if you ever do get into trouble (accident) or pulled in for an inspection while towing or something.

How quick is that cummins to smoke those 37"s through that 456 gear set?

Ridiculously quick. lol. Sometimes too quick as it breaks loose when I'm not actually wanting it too. I guess 1100 ft-lbs will do that ;)

456"s at a shop is like 1600$ I think..well worth it, u should get better mileage on the why as mds will activate easier.

Very likely that he'll get slightly worse mileage with the lower gears. The higher RPM you end up turning outweighs the other benefits. I lost about 0.5 mpg going from 3.73's to 4.56's. Totally worth it though as the truck is SO much better to drive.
 
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mtofell

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Thanks everyone.... lots of great info. I'll have to see how it all works out when I get a bigger RV. I likely won't even be over what the 3.73s are rated at but generally hate maxing out anything. I can't imagine the change to 4.10s is really big enough to justify the cost but who knows. It's kind of a ****** that about 90% or more of these trucks came with the gear ratio that no one seems to want given the choice.
 

KarL45

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As it seems many are considering re gearing, has anyone done any research into say, a 4.88 gearing? While 4.56 is a definite improvement over the 3.73 for towing, I think that a 4.88 may be optimum ratio especially if towing heavy and in the higher elevations. Initially I was a little unsure about the longevity of the 4.56 for towing heavy as the ring to pinion tooth contact is greatly reduced. Having almost 10k of towing with them, there seems to be no noticeable wear or slack. So far, so good. Will be able to fully attest to that after next years travels as planning on another 10k miles at least. One thing I would ask from some of you that are connected to a dealership and have diagnostic knowledge, is the pcm program different between the Ram with the 3.73 gearing and one with the 4.10 gearing. I am suspecting so but not sure.
 

brandonjansen

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As it seems many are considering re gearing, has anyone done any research into say, a 4.88 gearing? While 4.56 is a definite improvement over the 3.73 for towing, I think that a 4.88 may be optimum ratio especially if towing heavy and in the higher elevations. Initially I was a little unsure about the longevity of the 4.56 for towing heavy as the ring to pinion tooth contact is greatly reduced. Having almost 10k of towing with them, there seems to be no noticeable wear or slack. So far, so good. Will be able to fully attest to that after next years travels as planning on another 10k miles at least. One thing I would ask from some of you that are connected to a dealership and have diagnostic knowledge, is the pcm program different between the Ram with the 3.73 gearing and one with the 4.10 gearing. I am suspecting so but not sure.

I would never go to 4.88's unless you're planning to tow huge weight with large tires almost all the time. Simply because the truck will become almost useless when not towing. Honestly my 4.56's with 37's are already slightly overkill on my truck. When driving unloaded on the highway 4.10's would have been a better option. If I was driving more on the highway I'd be tempted to swap 4.10's into it now.

Programming isn't any different for the different gear ratio. The ECM could care less about what gears are in the truck.
 

KarL45

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Yes, the 4.88's or even the 4.56 gears aren't for everyone. Not sure of your average elevation in Canada but imagine in the 2 to 3k area. Here in the Rockies, at 6k and easily above, the 4.56 isn't any too high. Also, like you said, what you plan to tow for weight is also a factor. I pull between 13 and 14K so for me, knowing what I know now, would have went with the 4.88's. With the oem 18" wheel, I run only 2300 rpm at 80 mph. Still a very low rpm to speed ratio with the 6.4 power band.
 
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loveracing1988

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I would never go to 4.88's unless you're planning to tow huge weight with large tires almost all the time. Simply because the truck will become almost useless when not towing. Honestly my 4.56's with 37's are already slightly overkill on my truck. When driving unloaded on the highway 4.10's would have been a better option. If I was driving more on the highway I'd be tempted to swap 4.10's into it now.

Programming isn't any different for the different gear ratio. The ECM could care less about what gears are in the truck.
You have a Cummins correct? If so I can see why you think that high of a gear is overkill but in the 6.4 it should be perfect for 35's or 37's. With my 35's and 3.73's I am only running about 1350 to 1400 rpms at 65 mph and 1500 rpms at 70, generally gold for fuel mileage but it ends up lugging the motor so mds never kicks on and any Hill and it has to downshift.
 

brandonjansen

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Ya that is correct. Sorry, wasn't thinking about the Cummins/Hemi RPM range difference when I was typing up that last post. Definitely a different ball game when you have more RPM to work with.
 

riverss

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stock tire is 33" tall. which gear set would be better (4.10 or 4.56) IYO for pulling a 12 K R/V i have 373's now 6.4L 2500 and OK here in Texas but i think lower would be better at higher elevations especially in the mountains this truck is used exclusively for towing the R/V. I have not seen a torque graph so i do not know the optimum RPM range for this motor
 
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mtofell

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With my current 373s I just couldn't see spending the money to only go to 410s. Especially if your truck is mainly used for towing I'd say go for the 456s for sure. I use my truck 95%+ as a daily driver and still think the 456 is what I'll swap to eventually.
 

SilverSurfer15

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EDIT: I just re-read your earlier post... where you answered my question.
 
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RAM_Designs

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Very likely that he'll get slightly worse mileage with the lower gears. The higher RPM you end up turning outweighs the other benefits. I lost about 0.5 mpg going from 3.73's to 4.56's. Totally worth it though as the truck is SO much better to drive.

What size tires are you running?
 
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