4.10's to 3.55's diff's with a auto tranny

[fcluddington]

With fuel hovering at $4.25 per gallon I am looking at getting a set of 3.55 axles instead of the oem 4.10's I have been getting a constant 16 per gallon for years. I do pull a 38ft trailer 5-10 times per year. The complete axles are going to cost about $800 bucks. Am I looking at fuel savings the correct way or am I just gonna put to much strain on the Auto. Pros and Cons? 2001 2500 4.10 diff's with LSD automatic trannsmission 169,000 miles on truck and no current mods other than KN filter. thanks

[diesel4life]

If you plan on keeping your truck for another 10 years it may pay off unless you do a TON of driving it may not take as long...I think it would take a long time to recover 800 dollars in savings in fuel. The 3.55 gears work well for me with my auto there are a few times a year I wish i had the 4.10s. Maybe you could put an ad out on a few forums to see if somebody would be willing to swap you for gears?

[Rogan]

I believe (as an average) that most autos have 3.55s anyway. My 1-ton has 4.10s, but it was originally a 5spd (prev. owner converted it to an auto )I drive about 70% city per tank, and about 80% towing per tank, and average around 11.8-12.5 in my dually.You'll drop about 200-250rpm rpm at 60-65mph when going from the 4.10 to the 3.54s, but it may put your truck into it's sweet-spot.

[flagmanruss]

I suggest you skip the K & N oiled filter... oiled filters are not well regarded in tubodiesels. There are lots of dry elements including the huge BHAF (Big Honkin Air Filter) to choose from. I think the 3.55 stock axle ratio is much better unless one plans on much bigger tires. I HAVE 4.10s & consider it a bad choice... but I can't afford to change the axles so I'm stuck with it. There ought to be lots of trucks & wrecks with the 3.55s since that was the stock ratio.

[fcluddington]

For now I probably just stick with the KN seems how I have 2 filters and it's how I bought the truck. My tire size is 285 r16's. I drive about 50 miles a day. I was hoping with the 3.55's and Edge of getting into 21-24 mpg range. maybe that is not realistic. Truck is sitting right now while I drive my Honda go kart. Once winter hits I will be driving truck 100% of the time.

[Rogan]

For now I probably just stick with the KN seems how I have 2 filters and it's how I bought the truck. My tire size is 285 r16's. I drive about 50 miles a day. I was hoping with the 3.55's and Edge of getting into 21-24 mpg range. maybe that is not realistic. Truck is sitting right now while I drive my Honda go kart. Once winter hits I will be driving truck 100% of the time.

Right off the bat, I'd stick with the 4.10s. ESPECIALLY since you're running the 285s. Dropping to a 3.55 RP, you're gonna see a drop in fuel economy, especially in city driving.

If you're close 21-24mph range, count your blessings; especially with those tires. My '97 3500 with 4.10s, 235s, and auto will struggle to get 13mpg, and it's my only means of mobility. My old 2001 2500 with 235s, 3.55, 6 speed, Edge Juice, got best of 18, once.

I think M73M is an exception to the rule of the 24V society, when it comes to awesome mpgs (and hair. )

[JAG1]

Gosh for your own sake.... on the K&N filter....... you should open the intake tube between the turbo and the filter, run your fingertips inside and see if you have any dust at all. This where K&N got a bad rap cause guys were finding dust getting thru their filter.You don't need that cause turbo bearings are spinning over 100,000 times a second. Something like that. Can't remember everything:cookoo:

[flagmanruss]

Only rarely can I break 16 mpg... best of 18... all running light & trying for mpgs, with my 4.10 gears & 285R16 OEM Michelin... still on original tires the truck came with! Any time the wife drives the truck anywhere, I lose 1 mpg for the whole tank full. I would consider you 16 to be typical good mpg. Anytime I hit highway speeds, I'm over 2000 rpm with these tires (21-2200rpm) & the mpg falls off. The guys who have 3.55 axles can get 20 or slightly more. Even a 3.73 axle would be better.Now going to 17s or bigger tires would have the same effect... 17s are a common switch to allow for 3rd gen brakes to be retrofitted. I don't recall but I think a leveling kit is required to run 17s. When it's time for new tires, I will consider it.

[Rogan]

Only rarely can I break 16 mpg... best of 18... all running light & trying for mpgs, with my 4.10 gears & 285R16 OEM Michelin... still on original tires the truck came with! Any time the wife drives the truck anywhere, I lose 1 mpg for the whole tank full. I would consider you 16 to be typical good mpg. Anytime I hit highway speeds, I'm over 2000 rpm with these tires (21-2200rpm) & the mpg falls off.

The guys who have 3.55 axles can get 20 or slightly more. Even a 3.73 axle would be better.

Now going to 17s or bigger tires would have the same effect... 17s are a common switch to allow for 3rd gen brakes to be retrofitted. I don't recall but I think a leveling kit is required to run 17s. When it's time for new tires, I will consider it.

285s are not OEM. You have 265s, Russ

[flagmanruss]

Oooops! My Bad! That's what happens when I try to operate from memory. Yes, the 265s came on the truck as part of the several option packages it was loaded with. The standard size was smaller.So your 285s are already cutting into the 4.10 gears. Russ

[fcluddington]

Yes for my particular driving I am starting to have doubts about getting great fuel economy. Maybe I look into the running of propane. I am just bummed about the high ___ diesel prices currently. I think they are inflated in my area because of Harvest time.

[Ilikeoldfords]

I have thought about going to the 3.73's on my truck someday. I do a fair amount of highway travel and would like to go 70mph once in a while. With my 4.10's I have to keep her around 65 to break 18 mpg's. I have the 6 speed though. Does anyone have the 3.73's on the nv5600? What rpm's are you turning if you do? Just curious...