3.73 to 4.10 rear axle conversion.

[CROW]

Truck is an 05 dually with a six speed and 3. 73 rear axle. Tow a fifth wheel and a boat behind that sometimes. We're considering a new fifth wheel that would weigh about 2,500 lbs more than the one we have now and am considering the conversion to a 4. 10. Would like to have comments of those who have done this conversion: cost, RPM increase, effect on mileage, etc. , and does it really make a lot of difference with the six speed. Thanks in advance for any responses on this thread or by PM.

 

[AKaiser]

You won't need it, if you've already got the G56 manual transmission. If your reverse gear is left and down (next to 2d) you have a G56. Go to http://www.klenger.net/dodge/general-reference/gear-speed-calculator. xls and compare the gearing in the G56 w/3. 73s to the NV5600 (previous transmission) with 4. 10s. If you can't use the Excel Spreadsheet, try the PDF at http://www.klenger.net/dodge/general-reference/gear-speed-calculator.pdf



For example, at 2000 RPM in 6th, there's one MPH difference. Here's a 2000RPM comparison, going thru the gears, each speed. I used 2000 since that's roughly the lowest RPM where max torque begins in an 05.



---------------RPM 1 2 3 4 5 6

G56x3. 73 2000 8 14 24 37 50 64

NVx4. 10 -2000 8 14 22 33 46 63



Notice that it's pretty close other than 4th and 5th gear.

 

[CROW]

Thanks to AKaiser. I forgot, transmission is a NV-5600.

 

[AKaiser]

Just for my edification, what kind of fuel economy do you get now?

 

[CROW]

I get about 16 solo and about 9 towing my fifth wheel. It goes down even more when towing the boat behind the trailer. This is at highway speeds here in Oklahoma driving 70 to 75 solo and 65 to 70 when towing. Realize there will be a mileage penalty if go to the 4. 10. This last winter I ran into a fella towing oil field equipment who was towing 18,000 with a NV-5600 and a 3. 73.

Thanks for the chart. Not a lot of difference between the G-56 with 3. 73 and the NV-5600 with a 4. 10.

 

[AKaiser]

My G56 gives me about 17 with 33s all around, about 16. 3 on stock tires, on winter fuel. Mostly same as you, but I don't tow, yet.