4.10 change to 3.73 is bad deal

[CUMMINZ]

I tow a 17k 5er. Several months ago we changed from 4.10 to 3.73 expecting an extended RV trip out west this summer. I have always loved the 4.10s. With my 19.5 tires they also slow down the gearing. In the last two months we have towed 4,500 miles. From NC to Destin, Dallas, Denver, Laramie and Salt Lake. While in Destin area I had new towing transmission from Suncoast. I have found my Smarty runs best with controllable EGTs on 130HP.

This is my experience: Due to gearing and heavy rig, when running on interstates I struggle keeping EGTs under 1250 @ 70mph in 6th. gear. At 70mph the engine turns around 1500-1600prms. with many 2-6 degree inclines I find myself shifting into 5th and run there a lot. It is real obvious I will be moving back to 4.10s when I get home.

 

[Dieselnerd]

I always get 4:10's in my trucks. My fifth wheel is only around 15K but I like having some reserve towing power. I don't mind the slightly lower mileage when I'm empty. I bought this truck to be a towing machine and I want the ability to buy a larger fifth wheel if I want without being concerned about being able to tow it.

 

[RVTRKN]

Your better off with 4:10's, why did you change in the first place? I have always regretted ordering my 3500 with 3:73's. I have thought about going to 4:10's but the cost to the low mileage doesn't warrant it. I only have about 65k miles on my 07 3500.

 

[GAmes]

Although I have a 3.5 differential my final gearing is probably close to yours with 4:10s. With 215/85-16 tires and the AD version of the G56 I'm turning 2000 rpm at 60 mph. It might cost less to downsize your tires.

 

[kthaxton]

Did you swap gears hoping for a mileage gain? If so......that is a very long pay off time.

 

[m35a2]

When you shift into 5th, does your egt drop? (I expect that it would.)
What rpm in 5th vs. 6th?

You might find there's not much difference in mileage between 5th and 6th. If that's the case I'd probably just tow in 5th if it was me.

The new trucks have 342 gears as an option, by all reports they work pretty well.

 

[Cummins12V98]

On flat ground I could tow in 6th with 3.42's and 29K combined. I found overall it was best to keep in 5th at 1,750rpm @ 60 same as my current truck in 6th with 4.10's.

 

[CUMMINZ]

We stumbled upon yesterday travelling from Salt Lake to West Yellowstone, on my Smarty I changed the tune setting for the turbo from #3 to #4 which increased boost to max. My overhead milage increased by 4mpg and EGTs greatly decreased. There were still plenty grades the rig got down on its knees into 3rd. gear. 12V98 I would love to ride with you with the 3.42s and 29k up these grades.

 

[RVTRKN]

Even though the 3:42 works for higher HP and torque of the latest CTD, it won't be the same with an 07.5. I drove the 2014 2500 with the 3:42 and hated it. Although empty on Hwy was great mpg, loaded it struggled, in the city stop and go running to low of rpm.

 

[Cummins12V98]

"12V98 I would love to ride with you with the 3.42s and 29k up these grades."

No can do! Traded truck and rV on current 15 with 4.10's.

 

[Cummins12V98]

Even though the 3:42 works for higher HP and torque of the latest CTD, it won't be the same with an 07.5. I drove the 2014 2500 with the 3:42 and hated it. Although empty on Hwy was great mpg, loaded it struggled, in the city stop and go running to low of rpm.

I am betting you did not have the TH engaged. With the TH off on my 11 HO 68RFE it would be slow to accelerate. I always ran with TH and EB on as I do with 15 and AISIN.

 

[CUMMINZ]

Even though the 3:42 works for higher HP and torque of the latest CTD, it won't be the same with an 07.5. I drove the 2014 2500 with the 3:42 and hated it. Although empty on Hwy was great mpg, loaded it struggled, in the city stop and go running to low of rpm.

RVT, I can not tell a difference between the 3.73 and 4.10 in MPG.

 

[CUMMINZ]

Even though the 3:42 works for higher HP and torque of the latest CTD, it won't be the same with an 07.5. I drove the 2014 2500 with the 3:42 and hated it. Although empty on Hwy was great mpg, loaded it struggled, in the city stop and go running to low of rpm.

I ran my Smarty on 130 HP setting from Salt Lake to Yellowstone. My 07.5 with that setting is running 480HP and 910 TQ. It pulls well.

 

[RVTRKN]

I am betting you did not have the TH engaged. With the TH off on my 11 HO 68RFE it would be slow to accelerate. I always ran with TH and EB on as I do with 15 and AISIN.

No, I didn't turn on TH, that was my first option and I tried it for a couple of hundred miles, and the shift points did indeed change for the better. However it clunked a lot in stop and go traffic, the kind that is 40mph to 10mph to 40mph and on and on and on. I settled on paddle shifting it.

RVT, I can not tell a difference between the 3.73 and 4.10 in MPG.

Glad to hear that, I suspect my poor mpg when @ 23K GCW towing, is the 3:73.

I ran my Smarty on 130 HP setting from Salt Lake to Yellowstone. My 07.5 with that setting is running 480HP and 910 TQ. It pulls well.

I just did an experiment running my EFILive on #5 (high performance setting) and noticed 20% better mpg empty @ 10K GVW, however it goes into regen with more frequency, that negates the better mpg.

 

[CUMMINZ]

No, I didn't turn on TH, that was my first option and I tried it for a couple of hundred miles, and the shift points did indeed change for the better. However it clunked a lot in stop and go traffic, the kind that is 40mph to 10mph to 40mph and on and on and on. I settled on paddle shifting it.




Glad to hear that, I suspect my poor mpg when @ 23K GCW towing, is the 3:73.



I just did an experiment running my EFILive on #5 (high performance setting) and noticed 20% better mpg empty @ 10K GVW, however it goes into regen with more frequency, that negates the better mpg.

IMO about the gen 3-4 RAMs, Now after I have toad with 3.73s and 4.10s and with 450+HP... With RVs in excess of 15k the RAM needs 4.10s with the 68rfe. I think slight fuel mileage will be on the side of 68rfe. Best towing rpms are no lower than 1800rpms. There are truly very few highways that sustained grades are less than 2%. If you ever tow with RAM with 400HP or more you will wonder why RAM has not moved into those ranges. Even the newer trannys are having issues. RAM needs a bullet proof 8 speed transmission badly.

 

[RVTRKN]

IMO about the gen 3-4 RAMs, Now after I have toad with 3.73s and 4.10s and with 450+HP... With RVs in excess of 15k the RAM needs 4.10s with the 68rfe. I think slight fuel mileage will be on the side of 68rfe. Best towing rpms are no lower than 1800rpms. There are truly very few highways that sustained grades are less than 2%. If you ever tow with RAM with 400HP or more you will wonder why RAM has not moved into those ranges. Even the newer trannys are having issues. RAM needs a bullet proof 8 speed transmission badly.

I can agree with all this, but I'll add a forgotten fact, since the newer Rams with the 3:42 rear differential changed the perception of normal. The 5.9 and early 6.7 are basically the same engine. The higher HP/TQ with the 6.7 was designed to overcome the DPF/EGR and related EPA crap. That way the Dodge CTD would not have a perception of power loss, and run the same RPM's. The forgotten fact is that the efficient RPM's for mileage and power was 1800-2000 RPM.

The 2014 2500 CTD W/3:42 I drove, always wanted to shift to the highest gear as soon as possible, and would cause it to ping and shake at 1000 RPM at 50 MPH when i wanted to accelerate while in 6th gear. That's the main reason I paddle shifted it, not until I got up to 65MPH on the freeway.

 

[Cummins12V98]

"The 2014 2500 CTD W/3:42 I drove, always wanted to shift to the highest gear as soon as possible, and would cause it to ping and shake at 1000 RPM at 50 MPH when i wanted to accelerate while in 6th gear. That's the main reason I paddle shifted it, not until I got up to 65MPH on the freeway."

Selecting TH would have eliminated that problem. With my 11 HO I always engaged TH and EB same with current 15.

 

[RVTRKN]

"The 2014 2500 CTD W/3:42 I drove, always wanted to shift to the highest gear as soon as possible, and would cause it to ping and shake at 1000 RPM at 50 MPH when i wanted to accelerate while in 6th gear. That's the main reason I paddle shifted it, not until I got up to 65MPH on the freeway."

Selecting TH would have eliminated that problem. With my 11 HO I always engaged TH and EB same with current 15.

As I noted in past threads and in this Thread, I couldn't get past the clunking while in T/H mode. Maybe if I was at 20K GCW, it would have been better. But I felt it was very hard on the trans and U-joints running @ 10K GVW. If I were to buy a new 3500 DRW it would only be equipped with 4:10's, and I would not buy a SRW 2500/3500 68rfe/Aisin due to the 3:42 rear diff only standard. I'd have a hard time justifying the cost of an already high price CTD, then pay extra on top of that to convert the front/rear diff to 4:10 ratio, not to mention the loss of your warranty.

 

[CUMMINZ]

I can agree with all this, but I'll add a forgotten fact, since the newer Rams with the 3:42 rear differential changed the perception of normal. The 5.9 and early 6.7 are basically the same engine. The higher HP/TQ with the 6.7 was designed to overcome the DPF/EGR and related EPA crap. That way the Dodge CTD would not have a perception of power loss, and run the same RPM's. The forgotten fact is that the efficient RPM's for mileage and power was 1800-2000 RPM.

The 2014 2500 CTD W/3:42 I drove, always wanted to shift to the highest gear as soon as possible, and would cause it to ping and shake at 1000 RPM at 50 MPH when i wanted to accelerate while in 6th gear. That's the main reason I paddle shifted it, not until I got up to 65MPH on the freeway.

I do agree.