i ran the vin on a possible purchase of a 94 single cab 5 speed 4x4 2500 to find out the gear ratio. the dodge dealer (who popped up the vin) said the front was 3:55 and so by some doing some math he fugured the rear had to be 3;54. can that be right? rear is 3:54? obvious newby question: what gearing is the optimal all around fuel mileage gearing? thanks for your time.

 

I think people will use 3.55 and 3.54 interchangeably... I think the actual ratio is 3.54. The only other (I think) ratio available for our trucks is 4.10. 3.54 is obviously better for fuel mileage. I have 4.10s in the 2500, but my dually h as 3.54s and I would take the 3.54s over the 4.10s any day.

 

ya that is probably right..... i've seen before where trucks have 4.10 rear and 4.11 front.... but they interchange...


3.54 is typically best for fuel mileage

 

Tire pressure will make a bigger difference than the .01 ratio difference will

 

Those ratio differences is so the rear will always push the front a little - puts tension on the driveline - gears, u-joints, etc - keeps everything tight, prevents breakage as traction switches front-to-rear-to-front

 

thank you, question well answered. 3:55 and 3:54 are the same sort-of. thats what i wanted them to be.

 

3.54's or 3.55s both have 39 ring gear teeth, and 11 pinion teeth. 39/11 is 3.5454545. Round it properly to 3 digits, its 3.55. Just cut the numbers off after 3, its 3.54.

 

I'm pretty sure this is a myth/urban legend. As mentioned before, difference in tire pressure will matter more than .01 ratio.

The actual gear ratio for a "3.54"is 3.545454545454 etc and it repeats. So whether or not it's a 3.54 or 3.55 depends on how you round it off. Technically, 3.55 is proper. (see "round-to-even method here: http://en.wikipedia.org/wiki/Rounding)

Usually, the difference in whether a diff will be 4.10 or 4.11 is relative to the room in the case for a given pinion size. For example, if you have a Ford 9", you'll have a 37:9 toothcount. With a Dana, you'll have a 4.10 with a toothcount of 41:10

If you do research on gear ratio availability, you'll find that with almost ALL differentials, you can EITHER get a 4.10 OR a 4.11--not both. Front vs rear axle is not distinguished.

So if you're buying differential gears, don't waste time looking for that fictitious gearset that's .01 off to go with your other axle. Gear them identically as is properly done and don't worry about it anymore.

JH

 

Just saw this press release from American Axle ... Has anyone made this conversion yet? Looks New!

AMERICAN AXLE & MANUFACTURING INTRODUCES NEW EXCLUSIVE 3.42 POWERDENSE® GEAR SET DESIGNED TO IMPROVE FUEL ECONOMY
AAPEX Show Booth #1458

Detroit, Michigan, October TBD, 2007 – American Axle & Manufacturing (AAM), which is traded as AXL on the NYSE, today announced a new exclusive aftermarket 3.42 PowerDense® gear set for 2003 to 2007 Dodge Ram Heavy Duty 2500/3500 turbo diesel pickups. The gear set and its technology will be showcased at the Automotive Aftermarket Products Expo (AAPEX), October 31 through November 2.

AAM Aftermarket now offers Dodge Ram diesel pickup owners the 3.42 ratio gear set as an alternative to the numerically higher ratio gear sets that are currently available. The lower ratio set reduces engine rpm, which helps improve fuel economy under normal driving conditions which exclude hauling, climbing grades, or pulling a trailer.
The 3.42 ring and pinion is designed to fit inside the original equipment AAM 9.25-inch front and 11.5-inch rear axles without modifications to the transmission or the truck’s on-board computer. In pre-2007 pickups the front axle requires a new redesigned differential case along with new side and differential pinion gears. All 2007 models have the advantage of coming with a factory installed redesigned differential case, side and pinion gears making the installation process easier.
AAM PowerDense® Ring and Pinion Gear Sets

AAM utilizes state-of-the-art face hobbing to generate the gear tooth form in a two-cut process. This represents AAM’s latest effort to enhance NVH, durability, quality and reliability of its ring-and-pinion gear sets. The key advantage of a two-cut gear set occurs when the components are being hobbed or generated. Hobbing creates more surface area and equal tooth depth. This produces lower alternating bending stress levels while creating a more even distribution of loading across all of the teeth. The results are reduced levels of NVH and increased durability.

Another key advantage of the two-cut process is the use of continuous indexing. In the manufacturing process the gear teeth are generated simultaneously with uniform tooth spacing and no imperfections.

Additionally, the two-cut manufacturing process permits tighter backlash specifications between the gear and the pinion. Backlash is defined as the amount of free play between two gears in their operating positions. The results are reduced heat, NVH, driveline clunk and increased gear set durability.

Finally, two-cut manufacturing is an environmentally friendly process. Since the components are dry cut, the presence of a coolant medium at the point of engagement of a tool and a component is eliminated. Without coolant, no mists or smoke are produced.

Tough Stuff

AAM PowerDense® gear sets are made from high quality Society of Automotive Engineering (SAE) steel purchased only from approved AAM and OEM steel suppliers. Special high core hardenability steel is utilized to enhance the design and manufacturing process of the gear sets.

Made Even Tougher

The specified steel also lends itself to precision shot peening which extends the life of AAM PowerDense® gear sets. In this process spherical shot is targeted at the root of the gear teeth and bombards the surface, resulting in compressive stresses to combat fatigue loading. The compressive stress increases AAM ring-and-pinion durability and reliability.

AAM parts are also forged, lapped and heat treated to meet OE manufacturers’ stringent standards. Coordinate Measuring Machines (CMM) are then used to inspect the parts for accuracy.

AAM – Tough to Beat

AAM engineering teams have advanced the design and manufacturing processes of driveline systems, chassis systems and metal formed products since 1994. AAM designs, tests and validates its ring and pinion sets to vehicle manufacturers’ exact specifications. AAM’s on-going programs in NVH, thermal management, vehicle-system efficiency, dynamics and vehicle handling and other disciplines assure customers that the parts they are getting incorporate the latest product, process and systems technology.
For more information on AAM gear sets and other products and services, visit the Internet at www.aam.com or dial 1-800-299-AXLE.

 

Dana has 3.31's for th d80 already, which would be more applicable in this section. Wonder if Dodge is gonna start offering the 3.42's now.