2012 Differential.

[RustyJC]

Just for reference:

RPMs at 60 MPH in 68RFE 6th gear (dually tire sizes assumed):

4. 10 = 1612

3. 73 = 1466

3. 42 = 1344

If you want to know the engine RPM at any other speed for a given gear ratio, the formula is (RPM @ 60 MPH) x (new speed / 60 MPH). For instance, if you want the engine RPMs at 85 MPH in 6th with 4. 10s, it computes to:

1612 RPM @ 60 MPH x (85 MPH / 60 MPH)

1612 RPM @ 60 MPH x (1. 4166)

2283 RPM @ 85 MPH

Rusty

 

[EGroeneveld]

I'd personally opt for the 3. 73 gears since your in a high speed limit state and don't tow really that heavy. That said either the 3. 73 or 4. 10 gears is not going to be that big of a differnce for you.



Also the 4. 10 gears are pretty rare, I had to factory order my truck to get them.



Just my personal opinion. That said I do have the 4. 10 gears and haul a 5K truck camper and tow an enclosed trailer full of quads and a RZR. I'm happy with the 4. 10 gears and towing. Also ran (kind of empty) up to WA a lot in the 70 mph limits usual set cruise at 75 or so and it does just fine, truck is quieter then my wife's 2007 Camry inside.

 

[mpaulson]

Go to the web site link below and get the gear ratio chart and download it and save it. You can change the tire sizes and or gear ratios and the rest of the chart changes and it is accurate. just find your transmission and change the gear ratios to suit your self and look at the chart. I just did the 3. 73 gear swap to the 4. 56 and I cruise at 110km/hr at 2150 RPM. This is perfect for towing in six gear. When I start out from a stop you'd swear that I was in low range and I run through the gear quite quickly. I also notice that on my edge monitor that at this speed empty I used to run at about 35% load duty and now I float between 15% and 22%. That tells you something about this rpm, the engine is right in it's sweet spot, if i loose some speed, I hit the tourque curve at the high point, if I speed up, I hit the hp high point in it's curve.

www.klenger.net/dodge/general-reference/gear-speed-calculator. xls"]http://www.klenger.net/dodge/general-reference/gear-speed-calculator. xls

 

[Cummins12V98]

Go to the web site link below and get the gear ratio chart and download it and save it. You can change the tire sizes and or gear ratios and the rest of the chart changes and it is accurate. just find your transmission and change the gear ratios to suit your self and look at the chart. I just did the 3. 73 gear swap to the 4. 56 and I cruise at 110km/hr at 2150 RPM. This is perfect for towing in six gear. When I start out from a stop you'd swear that I was in low range and I run through the gear quite quickly. I also notice that on my edge monitor that at this speed empty I used to run at about 35% load duty and now I float between 15% and 22%. That tells you something about this rpm, the engine is right in it's sweet spot, if i loose some speed, I hit the tourque curve at the high point, if I speed up, I hit the hp high point in it's curve.

www.klenger.net/dodge/general-reference/gear-speed-calculator. xls"]http://www.klenger.net/dodge/general-reference/gear-speed-calculator. xls

Is your speedo correct with the gear change? That is the biggest reason I have not went to the 4:10's. Having only one year warranty on the gears does not bother me.

Harvey I agree the 4:10's would make the start effortless in comparison to what I have. I just don't hammer it from a stop, never have towed that way. I just roll into it as it starts moving.

Really would like to know for a fact about the speedo with the gear change.

 

[Cummins12V98]

Go to the web site link below and get the gear ratio chart and download it and save it. You can change the tire sizes and or gear ratios and the rest of the chart changes and it is accurate. just find your transmission and change the gear ratios to suit your self and look at the chart. I just did the 3. 73 gear swap to the 4. 56 and I cruise at 110km/hr at 2150 RPM. This is perfect for towing in six gear. When I start out from a stop you'd swear that I was in low range and I run through the gear quite quickly. I also notice that on my edge monitor that at this speed empty I used to run at about 35% load duty and now I float between 15% and 22%. That tells you something about this rpm, the engine is right in it's sweet spot, if i loose some speed, I hit the tourque curve at the high point, if I speed up, I hit the hp high point in it's curve.

www.klenger.net/dodge/general-reference/gear-speed-calculator. xls"]http://www.klenger.net/dodge/general-reference/gear-speed-calculator. xls

What did it cost for your gear change? Dave Smith wanted $1,800 for both axles, seemed like a great price to me.

 

[HBarlow]

Is your speedo correct with the gear change? That is the biggest reason I have not went to the 4:10's. Having only one year warranty on the gears does not bother me.

Harvey I agree the 4:10's would make the start effortless in comparison to what I have. I just don't hammer it from a stop, never have towed that way. I just roll into it as it starts moving.

Really would like to know for a fact about the speedo with the gear change.

I never "hammer" my truck from a start either but the difference is you have to use far more throttle input and allow more torque convertor slippage to get the load rolling than a 4. 10 geared truck does.

I don't know where the road speed input signal is obtained. If it comes from an ABS wheel sensor changing gears would require a correction. If the speed input is taken somewhere else it may not. Surely one of the dealer mechanics knows.

 

[RustyJC]

Actually, if it's coming from a tone wheel on one of the wheels or (more likely) the rear axle ring gear carrier tone ring, no speedometer correction is required. The number of wheel (or ring gear/axle) revolutions per mile doesn't change with a change in axle ratios - only the number of driveshaft revolutions per wheel/axle revolution changes. Speedometer recalibrations were required when the speed signal came from the transmission output shaft.

On my 2002 (with the Dana 80), the speed signal came from the rear axle ring gear tone ring. With the AAF in the 3rd and 4th generations, I haven't had any reason to find out where the speed signal is coming from.

Rusty

 

[Cummins12V98]

Actually, if it's coming from a tone wheel on one of the wheels or (more likely) the rear axle ring gear carrier tone ring, no speedometer correction is required. The number of wheel (or ring gear/axle) revolutions per mile doesn't change with a change in axle ratios - only the number of driveshaft revolutions per wheel/axle revolution changes. Speedometer recalibrations were required when the speed signal came from the transmission output shaft.

On my 2002 (with the Dana 80), the speed signal came from the rear axle ring gear tone ring. With the AAF in the 3rd and 4th generations, I haven't had any reason to find out where the speed signal is coming from.

Rusty

I hope you are correct. I figured the Service Manager knew his stuff, they do a lot of custom things there. Maybe next spring when I head back to the NW I will do the gear swap. Bad part is when I get there I will be tempted to drive a 13 Longhorn with all the bells and whistles!

 

[HBarlow]

Had to think about that for a minute. You're right. Wheel rotation speed would not change with gear change, only with tire/wheel change which we often see discussed here.

 

[mpaulson]

On the 3rd and 4th gen trucks the speed reading is from the tone ring that is attached to the ring gear in the rear diff. So a gear change does not change the speed reading, no calibration required. I had to tell my dealership this also! Not very confidence inspiring! If they are willing to do the gear swap for $1,800 for both axles, that is a good deal. My rear got changed when the dealer ship had to replace the whole rear axle assembly because they screwed up the wheel bearings when they did a diff rebuild and it messed up the spindle. It was at that point that I opted for the 4. 56 gear change since I had a choice that wouldn't cost any thing. I then a month later paid $1,300. 00 to have the front axle gearing changed to 4. 56, so $1,800. 00 for both sounds cheap. Make darn sure that they actually know what they are doing and you trust them. I just had my 4th axle rebuild in a year and a bit due only to poor workmanship!!!#@$%! First time last year was becasue of carrier gears chipping up. On that rebuild, they didn't clean out the houseing good enougth of the gear debree and this spring I had to have it rebuilt because of bearing race damage on the pinion. Poor workmanship!! On this rebuild (2nd) they did not have the wheel bearing nut retainer ring set up properly and it let loose on a trip while fully loaded in the mountains and it snapped the left axle shaft and melted the hub cap right off. Poor workmanship! This lead to the third rebuild which was a complete new axle assemble from NAPC with the gear change to the 4. 56, which had a whine at 80KM/HR right out of the shop and then developed a 60KM/HR whine a month later, hence the forth rebuild last week to fix the whining that wasn't only from me!

 

[Cummins12V98]

On the 3rd and 4th gen trucks the speed reading is from the tone ring that is attached to the ring gear in the rear diff. So a gear change does not change the speed reading, no calibration required. I had to tell my dealership this also! Not very confidence inspiring! If they are willing to do the gear swap for $1,800 for both axles, that is a good deal. My rear got changed when the dealer ship had to replace the whole rear axle assembly because they screwed up the wheel bearings when they did a diff rebuild and it messed up the spindle. It was at that point that I opted for the 4. 56 gear change since I had a choice that wouldn't cost any thing. I then a month later paid $1,300. 00 to have the front axle gearing changed to 4. 56, so $1,800. 00 for both sounds cheap. Make darn sure that they actually know what they are doing and you trust them. I just had my 4th axle rebuild in a year and a bit due only to poor workmanship!!!#@$%! First time last year was becasue of carrier gears chipping up. On that rebuild, they didn't clean out the houseing good enougth of the gear debree and this spring I had to have it rebuilt because of bearing race damage on the pinion. Poor workmanship!! On this rebuild (2nd) they did not have the wheel bearing nut retainer ring set up properly and it let loose on a trip while fully loaded in the mountains and it snapped the left axle shaft and melted the hub cap right off. Poor workmanship! This lead to the third rebuild which was a complete new axle assemble from NAPC with the gear change to the 4. 56, which had a whine at 80KM/HR right out of the shop and then developed a 60KM/HR whine a month later, hence the forth rebuild last week to fix the whining that wasn't only from me!

Wow, sounds like you went thru the ringer.

I would not typically trust the dealer for such a job but I have seen some really custom things come out of their shop. Dave Smith in Kellog, Idaho. I have had Randy's Ring and Pinion do gear swaps before and they know what they are doing. They wanted $3,500 to do the swap. Both prices were with OE parts. By the time I get back up that way next year the 13's will be out, I love my truck but I keep thinking about all the 13's have to offer. The salesman said they would give me a deal to swap gears if I bought the truck, they were true to their word.