Info. on 3.42 axle

[BOUNDERBOB]

June 1, 2010 Looking to buy 2010--2500-6. 7-4x4 -auto. -Big Horn, crew cab, short bed, and am considering 3. 42 axle ratio for(hopefully) good mpg. I have a 29ft. 5th wheel which I tow a short distance a few times a yr.

This truck will be my main transportation.

Please advise re: 3. 42 axle. Many thanks--------Robert

 

[DEM123]

June 1, 2010 Looking to buy 2010--2500-6. 7-4x4 -auto. -Big Horn, crew cab, short bed, and am considering 3. 42 axle ratio for(hopefully) good mpg. I have a 29ft. 5th wheel which I tow a short distance a few times a yr.

This truck will be my main transportation.

Please advise re: 3. 42 axle. Many thanks--------Robert

what's she weigh?

 

[robertyoke]

read this 3. 73 or 4. 10 ??? - Dodge Cummins Diesel Forum

one guy on there tows doubles @ like 30k gcw with 3. 42

 

[Hummin Cummins]

Towed my 32' single slide which weighs in at just under 10k loaded 900 miles one way with 3. 42's Towed real well, 65 mph kept me right in her sweet spot in 6th gear running about 1800 -1850 rpm. Averaged 12 mpg on that trip, currently getting 18-18. 5 back and forth to work empty with almost 8000 miles on her. Very pleased so far with this truck.

 

[Barry]

Hey Guys,



There is a whole lot of difference between the ratios of a bolt action trannie and the automatics... ... ... ... .



Do a final, final drive ratio on both options and then decide.

 

[BOUNDERBOB]

5th wheel weighs 9700 lbs. --- thank you for quick response

 

[67guzzler]

Hey Guys,

There is a whole lot of difference between the ratios of a bolt action trannie and the automatics... ... ... ... .

Do a final, final drive ratio on both options and then decide.

Barry is right -- I'd go 3. 73 with the auto and 3. 42 with the G56 manual.

The auto has a way overdrive in 6th (0. 63). I think the 3. 73 would work nicer on the highway when towing with the automatic.

Note: The default with the automatic, without dealer intervention is the 3. 73. The 3. 42 is a no charge option and the 4. 10 a $50 option. But the point is, 3. 73 is what most of the automatics have and it strikes the best balance.

I saw this chart below in another thread a while back:

G56 Manual w/0. 74 final drive ratio in 6th gear, 265/70-17 tires, 654 revs per mile @ 70 mph:
3. 42 axle -- 1931 rpm at 70 mph
3. 73 axle -- 2106 rpm at 70 mph
4. 11 axle -- 2321 rpm at 70 mph (combination not available -- just for comparison)

6-Speed Automatic w/0. 63 final drive ratio in 6th gear, 265/70-17 tires, 654 revs per mile @ 70 mph:
3. 42 axle -- 1644 rpm at 70 mph
3. 73 axle -- 1793 rpm at 70 mph
4. 11 axle -- 1976 rpm at 70 mph

The last column is the RPM's at 70 mph. Note that the 6 speed automatic with the 4. 11 isn't much worse on the highway than the G56 manual with the most economical option, 3. 42 -- Both around 1950 rpm's.

Just a guess but I'd imagine the fuel savings of the 6 speed automatic and the 3. 42 on the highway must be impressive at 1644 rpm's and makes the automatic possibly a better choice for highway cruising without a load.

But the 3. 73 is most likely the best ratio overall for the automatic.

I initially was search for an auto with a 3. 42 rear for economy but ultimately ended up with a 3. 73 rear and am quite happy.

 

[tp0d]

I have an auto with a 3. 73 axle... Wish now I would have got a 4. 10...

I run 70mph at approx 1700rpm, and it kinda seems the engine is lugging. At 80mph I`m at 2krpm, which is closer to the sweet spot. (i`ve read the sweet spot as recommended by cummins is 2100rpm)

I`m relatively happy with the 3. 73 and the auto, and I had posted here earlier I was going to order a truck with an auto+3. 42's. Man i`m glad I didnt do that. I probably would be running 1500rpm or less at 70mph.

get the 373s

-j

 

[HBarlow]

Dodge engineers rate the trucks with six speed automatic and 4. 10 differential(s) to tow several thousand pounds greater gross combined weight than with a 3. 73 or 3. 42.

The Dodge engineers have tested them and know best.

Fuel mileage will vary very little between the differential gear choices. Towing performance will vary much more.

 

[67guzzler]

Sure -- But that's the last nth degree of need for towing at the expense of all other uses. IF you need those last few thousand pounds most of the time, then yes, 4. 10 is the way to go. That's why the checkbox on the order sheet is there. Otherwise, the 3. 73 is the best all around rear with the 6 speed auto.

 

[AH64ID]

Assuming the same transmission the 3. 42 will have less tq to the ground at any given speed than the 3. 73 or 4. 10 equivalent. Will it be enough to notice? Maybe, maybe not.

The 6. 7 VGT does a nice job of making more tq down low than the 5. 9, so compared to a 5. 9 its probably a wash. I know my buddies 2010 3. 42's tow's similar in 6th as my 2005 5. 9 (NV5600).

Quick math using 1500 rpms, not counting tire size (numbers equal tq being put to the tires)

3. 42's
6th 1400
5th 1823
4th 2424

3. 73's
6th 1527
5th 1988
4th 2424

Across the board you will have 8. 3% less tq at the same rpm with 3. 42's over 3. 73's.

 

[AKorner]

Sorry to revive such an old post, but do you guys know if these #'s apply to the 2011. 5 HO 2500? Also the ratio availablility? My reason for asking is that when I was looking for trucks I tried like crazy to find a 3. 73 or 4. 10 truck w/the auto. I noticed on the sticker that some mentioned they had 3. 42 and others 3. 73 or 4. 10, I just assumed that if it said nothing that it came with the basic 3. 42 setup, and that is pretty typical of a car sold in SoCal- the dealers are all about mileage and entertainment systems. But if the above is true then a sticker with no listed gear ratio for an automatic would be 3. 73 by default?

 

[HBarlow]

I believe the 3. 73 is the standard differential. Another ratio would be an option.

 

[AKorner]

Ok, this is great! The dealer was assuming 3. 42 as well. Cant find the code, but there is a paper label on the top right of the axle that says AS173... Was worried I may have to change them out if they proved inadequate.

 

[HBarlow]

A competent dealer sales manager should be able to look in their spec sheets or ordering computer. Even the sales brochure should tell them what the standard gear set is.

Please don't buy a truck if you don't know that fundamental information. It's not my concern which gear ratio you prefer, but make certain you get what you want. Don't listen to an ignorant or lying salesman who doesn't know and will tell you anything to close the deal.

I would not take a free one with 3. 42 gears. I believe very strongly that the only viable choice for a truck that will ever tow anything is 4. 10 because of the double overdrive automatic transmission.

 

[AKorner]

Yeah, Its actually a long- long story about how I had to find this truck- but basically it boils down to getting everything else I wanted except the gears, then changing them out later if it proved to be unworkable.

The two dealers I went to here were both recommended to me, but one had to look at the Dodge website to try to figure it out, and the other said it was 3. 42 unless otherwise specified.

VERY little selection here unless I wanted a 1500, then the sky's the limit. It was really tough to find an SLT that had what I wanted (2500, 800lbs, 4x4, 4. 10 or 3. 73's, back up camera, LSD, bench seats, bedliner) without going up to the Laramie, and most of those were stickered at 56-59K. Unfortunately my online research didn't uncover the 3. 42 manual / 3. 73 automatic business and I thought I was just gonna have to settle for the gears or order a 2012... then I ended up needing the truck before September.

Found this one up in Sacramento, two dealers here in LA didn't want to do a swap, so I flew up there last week and grabbed it.

Thanks for the info though!

3. 73's should be good for me, I tow 10,000lb Generators about 10% of the time. Otherwise its mostly highway.