2012 Differential.

[Barbieri]

I currently own a 98. 5 2500 with the Diesel engine. I am researching the 2012, 2500 with the 6 speed auto and am stumped as to what differential I should get. I tow a 31ft Airstream at 9000lbs. I only tow about every other year. Places like Alaska, BC, Canada, California and Eastern Canada. Where I live in south Texas is just hilly and consequently the 4. 0 to me is not necessary. The question is with the 3. 73 or 3. 42 differential. I am inclined to the 3. 73 but am also considering the 3. 42. I have at times with the 98. 5 auto trans had to downshift to first. Like in Utah and Monarch Pass. I have researched back issues and didn't find any articles that answered my question. I would appreciate any and all help.

 

[HBarlow]

The question has been discussed numerous times here in TDR including a currently running thread. Have you tried reading previous posts?

You stated you have already made up your mind to ignore the information developed by Dodge engineers and published in Dodge truck brochures so what is it you are looking for?

 

[Barbieri]

I did not mention IGNORE. Please read it again and if you can direct me to the forum that is discussing this query please tell me where to fined it. I looked and found nothing. I don't visit this web site often. I just asked a question. I am looking for the currently running thread and what is the title of it. Have a nice day.

 

[Wertles]

You can't really compare your older truck rear differential to the newer differentials. This auto is a 6 speed with 2 overdrives. Even with a 4. 10 rear end, you will be pulling way less RPM's than you think. There are many threads with the exact rpm's turned with the different gear sets. No one is reporting any significant fuel savings with lower gears. My . 02, get the 4. 10 even if it is a daily driver. Less lugging of the engine for any load, the maximum towing capacity for your given truck, and who knows, maybe in a year or 2, you could have something much heavier to tow and you will not have to start a thread "How much does it cost to change to 4. 10?" Remember, you are the one who will be driving your truck, everything else on this site is just a suggestion.

 

[WMoroni]

I like my 3. 73s in my current truck just fine. Plenty of power to tow anything the truck is rated for and then some. I had 4. 10s in my last truck but it was a cab and chasis so its kind of like apples to oranges, unimpressive to say the least. I drove a truck with the 3. 42s and was also underwhelmed with it, just felt like it had a lack of get up and go.

 

[Barbieri]

Thanks. I was also thinking about the 3. 73. When you say underwhelmed what are saying? As I understand it the lower the ratio the better the fuel economy. With my 98. 5 going up Monarch Pass towing my trailer [9000 lbs] I had to drop down into 2nd and then 1st. At Wolf Creek Pass I went up in 1st and it light up my dashboard. I came through that OK because I was using lubricants that could handle it. Here in south Texas I have no problem with mountains and I generally won't be towing. In Eastern Canada there are very few if any mountains. I am trying to balance my needs with my purchase. Thanks.

 

[Barbieri]

Thank you very much. Your right. I don't do the type of towing that requires the 4. 0. I read that at high speed like over 70 the 4. 0 produces "NOISE" . Where as a lower diff doesn't. I know that my 98. 5 when it hits 70 just purrs like a kitten. When I bought it I was new to diesels. Didn't even consider the diff. This time around I know better or maybe too much. Now I am making a more educated purchase. Again thanks and if you can think of anything let me know. Have a nice day.

 

[NIsaacs]

Read the thread titled "3:73-4:10" on this 4th. gen. forum. It discusses your questions. Keep in mind the new 6 spd. auto has two overdrives so don't compare it to your current truck. Especially read Rusty's post explaining the ratio differences.



Nick

 

[rscurtis]

Keep in mind also that your '98 had 16" wheels, as opposed to the 17" wheels used on the newer trucks. 3. 54 with 16" wheels is the same effective ratio as 3. 73 with 17" wheels. As others have mentioned, the latest auto has a deeper overdrive ratio than any of the previous transmissions.

 

[rrnut-2]

I have the 3:42's, you will not see a difference in fuel mileage. I wish I had gotten the 3:73's instead, and I do like my 6 speed manual.

 

[rashwor]

I don't really belong here, but please don't beat me up for it. And I know this is apple to oranges, but here is my $0. 02. I have a '05 with 3. 73s with the NV5600 manual transmission. I tow 14k and it does just fine. If I had it to do again, I would do 3. 73s.

 

[Vaughn MacKenzie]

I don't know why Dodge even lets you select 3. 42 gears for automatic trucks, that's almost pointless unless you're getting a 2wd short box highway cruiser that's never intended to tow. I thought the 3. 42 was mainly intended as a solution for the manual trucks.

 

[HBarlow]

I don't really belong here, but please don't beat me up for it. And I know this is apple to oranges, but here is my $0. 02. I have a '05 with 3. 73s with the NV5600 manual transmission. I tow 14k and it does just fine. If I had it to do again, I would do 3. 73s.

An '05 had the early G-56 with low gearing and low overdrive ratio. 3. 73 gears were a decent choice for that transmission, not for the 48RE or 68RFE for towing a heavy trailer.

 

[AH64ID]

I currently own a 98. 5 2500 with the Diesel engine. I am researching the 2012, 2500 with the 6 speed auto and am stumped as to what differential I should get. I tow a 31ft Airstream at 9000lbs. I only tow about every other year. Places like Alaska, BC, Canada, California and Eastern Canada. Where I live in south Texas is just hilly and consequently the 4. 0 to me is not necessary. The question is with the 3. 73 or 3. 42 differential. I am inclined to the 3. 73 but am also considering the 3. 42. I have at times with the 98. 5 auto trans had to downshift to first. Like in Utah and Monarch Pass. I have researched back issues and didn't find any articles that answered my question. I would appreciate any and all help.

Honestly I would opt for the 4. 10's. I can't think of a single reason not to if you tow. The double OD ratio's of the 68RFE make 4. 10s run lower rpms at cruise speeds when empty, but offer 20% more torque to the wheels than a 3. 42 gear set and 10% more than a 3. 73 gear set.

Keep in mind also that your '98 had 16" wheels, as opposed to the 17" wheels used on the newer trucks. 3. 54 with 16" wheels is the same effective ratio as 3. 73 with 17" wheels. As others have mentioned, the latest auto has a deeper overdrive ratio than any of the previous transmissions.

The size of wheels has nothing to do with overall ratios. A 265/75/16 is roughly the same size as a 265/70/17, both of which were OEM sizes.

An '05 had the early G-56 with low gearing and low overdrive ratio. 3. 73 gears were a decent choice for that transmission, not for the 48RE or 68RFE for towing a heavy trailer.

As Rashwor put in his post he has an NV5600, which was the available transmission in early 05. It wasn't until mid model year the G56 was released. The NV5600 could be had with either 3. 73's or 4. 10's, whereas the G56 has only been offered with 3. 73's, and 08+ 3. 42's in a pickup. The C&C can get a G56 and 4. 10's, but that was after the higher gears were installed in the trans.



I have a NV5600 and 3. 73's, there are plenty of times I wish I had 4. 10's, about the only time I don't is when I am doing 80 empty or when pulling a grade in 5th at 65 mph. The 3. 73's do great, but sometimes that added mechanical advantage would be wonderful. I would get the lowest gear set offered if I bought a new truck today.

 

[rscurtis]

Keep in mind also that your '98 had 16" wheels, as opposed to the 17" wheels used on the newer trucks. 3. 54 with 16" wheels is the same effective ratio as 3. 73 with 17" wheels. As others have mentioned, the latest auto has a deeper overdrive ratio than any of the previous transmissions.

The second generation trucks did not use 265 cross section tires, they were 245's. Despite the taller aspect ratio, their diameter is smaller than the 70 ratio with 17" wheels. This is one of the reasons the third gen's were not offered with ratio's higher than 3. 73.

 

[HBarlow]

Gen II 3500s used LT235/85R16 LRE tires. I think the Cummins-powered 2500s did use LT265/85(or 75?)/R16 LREs.

 

[AH64ID]

The second generation trucks did not use 265 cross section tires, they were 245's. Despite the taller aspect ratio, their diameter is smaller than the 70 ratio with 17" wheels. This is one of the reasons the third gen's were not offered with ratio's higher than 3. 73.

As with 3rd gens it was an option for 265's or 245's, at least in late 2nd gens.



235/85/16 = 653 rev/mile

235/80/17 = 654 rev/mile



245/75/16 = 683 rev/mile

245/70/17 = 681 rev/mile



265/75/16 = 658 rev/mile

265/70/17 = 658 rev/mile

 

[Jeff Knight]

My 95 had 245 tires on it and my 02 had 265 tires on it from the factory. So they did use 265's on 2nd gens... Jeff

 

[Vaughn MacKenzie]

All 2nd Gens model year 2000-2002 came with 265/75/16s, when Dodge revamped the suspension across the line.

My '98 came with 245/75/16s, I took those off and put a set of 3rd Gen 265/70/17s on it. It only changed the speedometer accuracy by making it 3% slower. Holding the two sizes side by side there is little height difference, at least when you're comparing Michelins.

Vaughn

 

[HBarlow]

Vaughn,

No, not exactly. The Ram 2500s had LT265/85/R16 but the 3500s had LT235/85/R16s. GMs had LT245/75/R16s/