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Gear Axle Ratio change 3.55 to 3.92

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Old 08-31-2007, 07:44 PM
HemiDen HemiDen is offline
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Default Gear Axle Ratio change 3.55 to 3.92

It turns out our dealer was wrong about the SLT 4x4 5.7L Hemi Durango we purchased having 8,750 lbs towing capacity. What has been learned by the dealer since is the towing capacity numbers shown in the brochure that we were assured were correct are incorrect. TheDurango comes stock with 3.55 gears whichequals to 7,250 lbs towing with the 5.7, where the $40 sticker option for the 3.92 axle ratio was needed to get the 8,750 lbs towing capacity the dealer said the truckDurango was capable of.

I am awaiting to hear back from the dealer in how this problem will be resolved since as we stated to them from the beginning that we needed the Durango to pull 7,299 lbs, but in the meantime I am wondering what problems would there be if the dealer chose to change the 3.55 gears to the 3.92's? Is it just changing the gears in the rear end, or is there more issues that can arise that effects the rest of the powertrain or anything else that would have to be adjusted?

Thanks for any input...
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Old 08-31-2007, 08:45 PM
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Default RE: Gear Axle Ratio change 3.55 to 3.92

They would have to swap the front and rear gears otherwise if you ever used 4wd the front would be pulling the rear around and we don't want that, other than that a quick reprogram of the comp to calibrate the speedo and your good to go. Definitely a job worrth the $40 before it is driven off of the lot. Did you get anything in writing stating it has the 3.92's???
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Old 08-31-2007, 10:26 PM
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Default RE: Gear Axle Ratio change 3.55 to 3.92

I'll know next week which method the dealer goes with to remedy the problem. The salesman already did a regional search to see what 3.92 equipped Durangos are out there and there are a handful, but none with the SLT "E" package and the options we have on our Durango, so that would lead to the optionofswapping out the 3.55's for the 3.92's, which I would prefer they do as we love the way this Durango is with all of it's options, especially since you mention it's should be a straight forward process, including the recalibration of the speedo. I hope this is a heads up as well to anyone buying a Durango looking to use the brochure's advertised 8,750 lbs tow for the 4x4 5.7L. I have full confidence it will be resolved just fine, this is an excellent dealership who I have purchased from many times, and in this case they have acknowledged there was an understanding the truck towed the full 8,750 as we discussed in length before the purchase how the Durango would be needed to pull our travel trailer. Yes, I wish the dealer knew that the little $40.00 3.92 gear ratio option was needed, but we'll work through it.I'll post the outcome whwn it's done.
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Old 09-01-2007, 08:38 PM
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Default RE: Gear Axle Ratio change 3.55 to 3.92

Well good luck with this, I hope the dealer doesn't try and take a dump on you over it, but I guess if they are looking at other D's they must be happy to help.
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Old 09-01-2007, 09:57 PM
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Default RE: Gear Axle Ratio change 3.55 to 3.92

Mean:

Recall that the Gen 2 D's 4x4s are all full time, so both gearsets would need to be changed ASAP as you said or the T case would blow in short order.

Don
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Old 09-02-2007, 06:24 PM
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Default RE: Gear Axle Ratio change 3.55 to 3.92

I did not know it was a FT4wd setup, I guess you learn something new every day.
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Old 09-06-2007, 01:13 PM
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Default RE: Gear Axle Ratio change 3.55 to 3.92

Also, for more FYI,

Hemiden,

Changing from 3:55 to 3:92 gear ratio will lower your MPG rating also as your engine will be spinning at higher RPM's to maintain a set speed. By how much, I do not know, but you will definitely see a loss in MPG.

If you need to only pull 7299 or roughly 7300 lbs, You may want to opt for a 3:73 ratio. This is a good middle range ratio that is good for towing and highway driving to keep your MPG from doing down the drain.
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Old 09-06-2007, 01:31 PM
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Default RE: Gear Axle Ratio change 3.55 to 3.92

Check out http://www.4lo.com/calc/geartable.htmIt has a chart that shows the raio thats best for fuel economy and power using your tire size. GOOD SITE.
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Old 09-06-2007, 09:05 PM
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Default RE: Gear Axle Ratio change 3.55 to 3.92

Kensai:

A change to a lower gear does not always equate to lower fuel economy. While it is true that a lower gear at a give speed equals higher rpms, local and around town driving can actually see an increase in mileage because you don't have to use as much throttle to get the vehicle moving.
I would agree that hwy would suffer as you will spend the most time in the upper rpm ranges.

Also, the Gen 2 D's have a reverse cut front gearset, and as such the only source I am aware of so far for gearsets that will work is though DC. They only offer the 3.55 and 3.92.
Going from a 3.55 to anything less than a 3.92 or even better 4.10 (when and if they are made in reverse cut) is the way to go. Changing your ratios less than .5 will not make enough difference to justify the labor which is the same no matter what ratio you choose.

Don
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Old 09-11-2007, 07:04 PM
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Default RE: Gear Axle Ratio change 3.55 to 3.92

Does anyone know what it would cost to have the swap done. My parents have an 05 with the same problem. The dealer lied and they just figured it out last weekend.
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Old 09-11-2007, 07:04 PM
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2003, 355, 392, 410, 4x4, axle, capacity, change, cost, dodge, durango, gear, gears, ram, ratio, tow

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