Overdrive or Taller Gears for Fuel Savings

[CCaldwell]

3.42 ratio

Have made contact with Bob Dunn at American Axle and he stated the gear sets would be avail. on 1 Nov. This date has come and gone so I made contact with BLUMENTHAL in O. K. C. to check on progress on 3 Nov. with no response so far. I feel AA is wasting their time with a 3. 42 axle and a 3. 36 would be more beneficial. One explanation of why the sixth gear is geared so low on the G56 is due to the origin of the transmission. It is designed to be used in the Mercedes Benz trucks in Germany and the speed limit is limited to 100 KMH (60 MPH) on the highways for trucks. At this speed the motor is in its sweet spot and any overgearing would be needless. The mileage readings I'm getting are 12. 9 on highway at 75 MPH (2450r. p. m. ) and in town/ country roads 13. 8- 14. 1 with a top speed at 60 MPH. OBVIOUSLY the truck is geared too slow for the U. S. roadway. Its amazing the fine folks at DODGE did not think this through when they opted for these ratios in the transmission and rears.

 

[Bernie]

No, it hasn't improved. Do a hand calculation and compare. Dodge made some change that when you reset starts the "average" from the last millage instead of from zero (which is correct). Dodge did this to keep big numbers seen if you reset while pulling or coasting a hill not to upset customers.



It is BS. The Chevy and Ford get better millage, so Dodge changed their fairly accurate MPG gauge to a lie-o-meter to show better millage. Total BS.



I started a post on this with a question a while back. look at my posts and you'll see it.



This and the lie-o-oil pressure gauge (it is calculated, not actual) have me thinking, while the Cummins is great, the Dodge portion of the equation is suspect. What does it say about a company's ethics and practices when it lies to owners every day through gauges they paid for!



When the Toyota Tundra "grows up" in 2008 with a 3/4 and 1 ton diesel version we will have to see if the Cummins is enough to keep people coming back to Dodge (and Ford and Chevy for that matter) to be lied to. My last Toyota was built in the USA. My Dodge was built in Mexico.

 

[DPKetchum]

I sure wish my NV5600 had a lower 1st and reverse like a G56. The first and reverse in a NV5600 does not move big loads or even no loads(reverse) slow worth a darn.

 

[CCaldwell]

gears 05-3.73 vs 07- 4.11s

Have recently driven a new 3500 HD chassis cab with the diesel, 6 speed man. , and of course the 4. 10 rears. Compared the R. P. M. s to the current 05 with the 6 man. and 3. 73 rears and this is what I found:

At 2000 R. P. Ms both trucks ran 50 M. P. H. in 5th gear.

At 1600 R. P. Ms both trucks ran 50 M. P. H. in 6th gear.

( Dealer rep in cab- couldn't gouge on it, also in town)

Both trucks have the same 17 inch tires. This leads me to conclude that the new 6 speed has different gears in the transmission or D. C. messed up and inadvertently put 4. 11s into my 05 and labeled them 3. 73s as listed on the dealer build sheet. Maybe the new truck has 3. 73s and was mislabeled to clear out old 3. 73 existing inventory? The tires on the 05 have only 19k miles on them so I don't think that amount of tire wear could account for this R. P. M. quandry. Any ideas ANYONE?

Can't wait for the new 4500/5500 trucks to come out. Maybe they will have a different rear axle- anything but the A/A (We offer you only one ratio so be happy with it) gears. STILL WAITING ON 3. 42s

 

[cojhl2]

The tires on the 05 have only 19k miles on them so I don't think that amount of tire wear could account for this R. P. M. quandry.

Tire wear has no effect on the relationship between Tachometer and Speedometer.

 

[Cattletrkr]

I got an e-mail back from AAM today:



Your interest in AAM product is much appreciated. AAM will have a 3. 42 ratio available for your vehicle in early 2007. All AAM differential components are available through qualified distributors.



You can contact me in early 2007 for update regarding 3. 42 availability. In addition, you can contact our distributors for product. Let me know where you live and I will provide a distributor/s near you.



So, I will wait and try them when they become available. It won't be as great a drop as an overdrive, but it should cost a lot less. I can also keep my old gears. Should I hate it, I can change back.

I know the mods don't like this, but .....















... ... BUMP.

 

[GeoffParker]

Bout Damn Time!

I know the mods don't like this, but .....



... ... BUMP.

Glad to hear AAM is going to have the shorter geared rear end for our beloved G56 trucks... ... yeah I have the GV Over under unit... ... But I'll be buying more trucks and will use the AAM on those.



I will be interested in the cost..... Any idea what the RPM's will be in 6th cruising at 70mph?..... I know there is a way to calculate it but I'm too busy to look for it.

 

[GColeman]

I was seriously thinking about purchasing one of these units as well... until I realized their limitations. US Gear allows the use of exhaust brakes, but requires a 2-second wait before engaging... it seems like you would loose a lot of momentum waiting 2 seconds for a shift. The Gear Vendor unit is not compatible with exhaust brakes. If a company develops a product that can be shifted quickly and allow the use of the exhaust brake, I'd be interested...

I had a US Gear on my 97 CTD with NV 4500 and 4:11 gearing. The best mod. I ever made. 2wd, 4wd, spit gears... . it allows it all.



Regarding the 2 second delay to shift: What that means is you pull the switch while accellerating, it takes about 2 seconds for the elec. motor to build pressure on the spring, the unit does not shift until you take release pressure off of the drivetrain (as in pushing in the clutch) at that point the shift is almost instant and when you release your clutch, you are in OD. It's just a matter of anticipating your up or down shifts. It is really very quick and smooth once you get the hang of it.

 

[Ereynolds72]

So has there been any update on the availability of the 3. 42 gears? I'm in the market for a new truck and would love to have a 6spd but I can't handle those highway rpms.



Klenger put this spreadsheet out a while ago. It's a good tool to play with tire sizes and gear ratios. Thanks Klenger.



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

 

[Bernie]

AAM Came Through

I got an e-mail last week from the guy that I e-mail at AAM last year (they remembered!). Here is what they sent:





To convert GM to 3. 42 ratio:



Rear



11. 5” Gear Set – 40045439 (New) - (Fits both GM and Chrysler 11. 5 Rears)



Front



9. 25” Gear Set – 26060068







To convert Chrysler (Dodge Ram) to 3. 42 ratio:



Rear



11. 5” Gear Set – 40045439 (New) - (Fits both GM and Chrysler 11. 5 Rears)







Front – A Diff Case and Diff Kit change is necessary for 2003 to 2006 models – use the following parts…



9. 25” Gear Set (New) – 40045288 – (used in 2007 and up)



9. 25” Diff Case (New) – 40028204 – (used in 2007 and up)



9. 25” Diff Kit (New) – 74042462 - (used in 2007 and up)











Bill Laughman



American Axle & Manufacturing



Sales Account Manager



-- email address removed --



Tel: 313. 758. 4598



Fax: 313. 758. 3826

 

[WOT]

Well the front axle sure sounds like it will be pricey to convert!

I wonder if this means you will see it as on option on new trucks - an axle swap with a new ram owner who wants better tow gears sure sounds cheaper.

 

[birddog]

there has been a lot of discussion by various people about 3. 42's. They are available and it sounds like a few are ready to try it. Sounds like it will cost about 600 bucks. I will probably change mine in the future if this seems to be working. However if the 3. 42's cause a lack of power, in which they shouldn't by my rpm calculations it wouldn't be worht the little fuel savings

 

[steved]

The gears and spacer run $800 (front and rear)... I already asked on another board.



The front axle requires a ring gear spacer to make it work... as soon as they told me that, I decided to stick with my 4. 10s. I have seen one too many issues when a ring gear spacer was used.



steved

 

[TowPro]

I just did a trip through NE of PA up to lake george towing my 10K camper.
One section of road runs 45mph for around 20 miles of level ground. I drove 10 miles in 5th gear, showing around 12mpg on the overhead. I drove the next 10 miles in 6th gear, showing 15mpg on the overhead.

5th to 6th is about 600rpm different. by setting the cruse control at 45, the wind load don't change, only the truck RPM changes.

I sure can't wait to hear the results of the 3:73 to 3:42 switch in real numbers.