Improving overdrive in my 2007.5

[AHarris]

After finally getting to drive this truck (see sig), I have to say I love this beast! Plus, I've driven cars that are harder to shift than this G56--it's smooth and precise! The only complaint is the RPMs seem a little high for my liking at 70 mph--she's turning 2100! The reason I didn't get one with the auto is I got such a low price on this particular truck through AAFES Car Sales that I practually stole it at $31K and some change!



Right now it has 3. 73s with the G56. Drives great but seems to need a

7th gear! Seems I have a few options to improve this:



- Bigger wheels/tires (est cost around $1,500 total)

- Swap the 3. 73 ratios out for 3. 42 (cost ????) (how badly would this affect towing?)

- Install a gear vendors unit (cost ????)

- Just live with it (will it hurt the Cummins to spin it at 2400 running 80-85 down the interstate?)



Would appreciate recommendations from you smart guys out there. Looking for the most cost effective approach.

 

[RVTRKN]

Hi Yooper39, its been a while, I remember the thread you started when you where looking into the new 6. 7. All I can say is tow with it first before you change the gearing. I have both NV5600 and the G56 they both run at 2100 RPM at 70 and you do sometimes catch yourself trying to shift into 7th. However when you tow, those numbers are awesome at that speed. It seems to be the correct RPM when towing flat and slight grades and when you encounter a steep grade, down shift to 5th and keep your RPM at 2300-2500 for cool EGT and you wont want to change the setup. I thought about the Gear Vender unit myself until I towed my 5ver all over the Pacific NW, I wont waste my money now, I believe the setup is perfect for heavy duty operation.



BTW welcome home and thank you for your service to our Country.



Steve...

 

[RVTRKN]

And BTW that is a very nice looking truck.

 

[Giachino]

Off topic, so my appologies... . but had to say the following since you're in Germany



1. get the smarty (when available) with speed limiter removed... . and drive that bad boy on the autobahn



2. Did you make it to Oktoberfest? I'm hopping you're a beer drinker as you're a lot closer than most of us... . this year was my first year... . plan on going every year i can make it... . Awesome



3. Thanks for serving our country



4. Nice truck

 

[RHestand]

After finally getting to drive this truck (see sig), I have to say I love this beast! Plus, I've driven cars that are harder to shift than this G56--it's smooth and precise! The only complaint is the RPMs seem a little high for my liking at 70 mph--she's turning 2100! The reason I didn't get one with the auto is I got such a low price on this particular truck through AAFES Car Sales that I practually stole it at $31K and some change!



Right now it has 3. 73s with the G56. Drives great but seems to need a

7th gear! Seems I have a few options to improve this:



- Bigger wheels/tires (est cost around $1,500 total)

- Swap the 3. 73 ratios out for 3. 42 (cost ????) (how badly would this affect towing?)

- Install a gear vendors unit (cost ????)

- Just live with it (will it hurt the Cummins to spin it at 2400 running 80-85 down the interstate?)



Would appreciate recommendations from you smart guys out there. Looking for the most cost effective approach.

I went with bigger tires and wheels. New BFG 315 Hummer 2 take-offs.

I was able to pick up a set locally that I bought on E-bay ($650).

I measured the roll-out, the 315s are about a 10% increase.

The higher gearing not only helped cruise RPM, I also liked it for my second gear standing starts. (Stock, second gear too low, third gear too high. )

IMO the larger tires also look better.

I was hoping to increase my MPG, but it stayed pretty much the same.

The H-2 wheels have to have their center holes enlarged and there are threads on this sight as to how to do this.

It worked for me.

Ray

 

[mattymac]

The bigger tires increase load, usually alot of stop and go will hurt mileage with bigger tires.





RVT, there has to be some diffrence in RPM between the nv and the getrag since their OD ratio is diffrent and you have the same gearing? Or is it just not that much of a diffrence?

 

[AHarris]

Thanks

Hi Yooper39, its been a while, I remember the thread you started when you where looking into the new 6. 7. All I can say is tow with it first before you change the gearing. I have both NV5600 and the G56 they both run at 2100 RPM at 70 and you do sometimes catch yourself trying to shift into 7th. However when you tow, those numbers are awesome at that speed. It seems to be the correct RPM when towing flat and slight grades and when you encounter a steep grade, down shift to 5th and keep your RPM at 2300-2500 for cool EGT and you wont want to change the setup. I thought about the Gear Vender unit myself until I towed my 5ver all over the Pacific NW, I wont waste my money now, I believe the setup is perfect for heavy duty operation.



BTW welcome home and thank you for your service to our Country.



Steve...

I appreciate the kind words from you and Giachino. I wasn't sure I'd like the blue but when I first laid eyes on it it grew on me--in about 30 seconds! I'm still in Germany until May--my brother is keeping the truck stored for me but I was back for a TDY and did about 300 miles worth of gentle break in driving over the weekend. I almost had to pry myself out of it so I could get on the airplane and head back to Stuttgart.



I think I will take your advice, Steve, and see how it does with the camper for the first year. Plus, a 5er is on our near future in the next couple of years. When towing, I'd keep it under 70 for sure. My only concern with the G56 setup (and I have the AE ratio with the . 74 OD) is that when I'm unloaded I like to run around 80, which spins the Cummins 2400-2500... will that high RPM used regularily for unloaded highway driving affect long term durability of the engine?



Here's a couple more pics of the truck:

 

[AHarris]

Pictures

I went with bigger tires and wheels. New BFG 315 Hummer 2 take-offs.

I was able to pick up a set locally that I bought on E-bay ($650).

I measured the roll-out, the 315s are about a 10% increase.

The higher gearing not only helped cruise RPM, I also liked it for my second gear standing starts. (Stock, second gear too low, third gear too high. )

IMO the larger tires also look better.

I was hoping to increase my MPG, but it stayed pretty much the same.

The H-2 wheels have to have their center holes enlarged and there are threads on this sight as to how to do this.

It worked for me.

Ray

Do you have a photo of this you could upload?

 

[AHarris]

A personal favorite Hefe Weizen!

Off topic, so my appologies... . but had to say the following since you're in Germany



1. get the smarty (when available) with speed limiter removed... . and drive that bad boy on the autobahn



2. Did you make it to Oktoberfest? I'm hopping you're a beer drinker as you're a lot closer than most of us... . this year was my first year... . plan on going every year i can make it... . Awesome



3. Thanks for serving our country



4. Nice truck

See below for answer to #2:

 

[Loren]

RVT, there has to be some diffrence in RPM between the nv and the getrag since their OD ratio is diffrent and you have the same gearing? Or is it just not that much of a diffrence?

mattymac,



The NV5600 top gear (6th) ratio is 0. 73:1. The new G56 transmission top gear (6th) ratio is 0. 74:1. I don't have the figures for the Getrag. RPM in 6th for both transmissions should be within a dozen RPM of each other.



Loren

 

[Loren]

My only concern with the G56 setup (and I have the AE ratio with the . 74 OD) is that when I'm unloaded I like to run around 80, which spins the Cummins 2400-2500... will that high RPM used regularily for unloaded highway driving affect long term durability of the engine?

Yooper39,



It has been a long time since I saw it so I can't remember whether it was on these forums or in the magazine, but someone (I think it was Robert Patton) called Cummins and asked that same question about the 5. 9 liter engine.



The Cummins guy told the caller, "You can run that engine at the redline all day long. " I'm sure that this applies to the new 6. 7 liter too, especially since the actual load is light compared to the trucks it's intended for. (UPS-type trucks, medium dump trucks, etc. )



I think that high RPM operation may reduce your fuel economy somewhat, but I'm sure that it won't hurt the engine.



Loren

 

[Loren]

I have both NV5600 and the G56 they both run at 2100 RPM at 70 and you do sometimes catch yourself trying to shift into 7th.

On my 2000 truck (now totaled) I had the U. S. Gear overdrive behind the NV5600. It was the best of both worlds. In 6th gear - overdrive, I was turning about 1650 rpm at 70 mph, with 3. 54 differential ratios.



I have been told by a U. S. Gear rep. that my overdrive won't fit behind the new G56 transmission, but a former employee says he has heard of its being done. I ordered the truck with 3. 74 differentials with the hope that I can install my overdrive in the new 2008 truck. It will be a while before I have an answer, but I'll try to remember to post my findings. If it works, that will be the ideal setup.



Loren

 

[mattymac]

mattymac,



The NV5600 top gear (6th) ratio is 0. 73:1. The new G56 transmission top gear (6th) ratio is 0. 74:1. I don't have the figures for the Getrag. RPM in 6th for both transmissions should be within a dozen RPM of each other.



Loren

I was thinking the G56 was more like . 78??? I never really paid that much attention to it since im not a big fan of the design compared to the nv5600.



. 73 to . 74 isnt even a noticeabe diffrence on the tach.

 

[Loren]

I was thinking the G56 was more like . 78??? I never really paid that much attention to it since im not a big fan of the design compared to the nv5600.



. 73 to . 74 isnt even a noticeabe diffrence on the tach.

mattymac,



I got that 0. 74 number from the 2008 Dodge Commercial sales brochure. It's full of good information, including the ratios for the G56 and 68RFE transmissions.



I liked my NV5600 transmission, but on the test drive the new G56 shifted much more easily. My NV5600 never went into first gear at a stop very well and sometimes required starting in second when I couldn't get it in at all when the light changed. The new G56 is nice. I'll have a better idea after my new truck comes in.



Loren

 

[gsbrockman]

Would appreciate recommendations from you smart guys out there. Looking for the most cost effective approach.

I don't claim to be smart, but I certainly can't argue with you in the Color Selection Department. :-laf



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Your most economical route is to upgrade to some LT285/70R17 or LT295/70R17 tires. In addition to filling out the wheel wells, you'll probably get a little improvement on final drive ratio. In addition, the dealer can modify your calibrations up to the LT285/70R17 size. Anything larger than an LT295/70R17 (IMO) will start to rob mileage due to added weight and increased rolling resistance.



Don't get all excited thinking the tire swap will increase fuel economy alot. These 408 ci's and emissions crap will still not get great mileage, even if you lower the engine rpm via tires. My truck, w/LT285/70R17 Firestone Destination A/T's, only turns 1,350 rpm @ 55 mph (speedo dealer corrected).



Thanks for your service to our country.



Greg

 

[Motorhead]

NICE truck. I bought a new '07, 5. 9 4X4 G56 with the same 6th gear ratio you have. I did some research and a set of 285/75/17's are the way to go. I computed it that I will be running just under 72mph @ 2,000rpm. Guys on the site that I asked said they didn't hurt their mileage. Most said they picked up 1mpg. I PERSONALLY find that if I can keep the RPM's at or below 2K the truck gets its best mleage. With 4,000 miles on mine, I have gotten 19. 5 on a trip to Los Angles and back.
I just put the SMARTY jr on today and what a difference! I am on the 40hp mode.

HEY... . Thanks also from me and my family for your service to our country!!! Chris

 

[Motorhead]

I was thinking the G56 was more like . 78??? I never really paid that much attention to it since im not a big fan of the design compared to the nv5600.

. 73 to . 74 isnt even a noticeabe diffrence on the tach.

mattymac, The 6th gear ratio was changed somewhere in November to December of '06. My '07,5. 9 has the taller 6th gear. It was built in December of '06. The trans code was AE for the 5. 9's. Of course I wouldn't have learned this if it wasn't for this site!!
I bought my truck out of dealer stock. I had to hunt for the LATE 5. 9 production so I got the right 6th gear. STILL, it is a change from what I had before. My old truck was a '01. 5 with auto and 3. 54 gears. It ran well but I wanted a stick for towing.

 

[SBeretz]

Yooper, you can put Toyo 285/75's on your truck. Those will drop your RPM's about 150-200RPM's and they are a really nice tire. I have the older G56 and needed to get my RPM's down a little, but the others are right, don't go too big as it will sacrifice your towing power, which is why you bought the truck. I would never go any bigger than what I have and may step back down to a 285/70 in my next set of tires. Scotty

 

[RVTRKN]

Yooper39, you can run it at any RPM you want as long as you dont go over 3000 RPM all day long. It is the biggest difference between the Cummins and the compitition. The G56 is not a getraug trans, however there is a great article a couple of TDR issues ago on the difference between the G56 and the NV5600 and has details you might want to know. It was the article that convinced me to go ahead with the manual vrs the 6spd auto, when I ordered my C&C. Don't forget to have the idle control activated, it will be the best $100 you have spent.