I have read a number of posts about gear changes ... 3.55 to 4.10 or 4.56 and how the 3.55 is a "real dog" gearset. I don't argue about the 3.55 being a dog.

I want to make the change but the affect on MPG is my concern. I run probably 60-70% city type (under 50mph) driving. I tow once or twice a year at the moment but haul truckloads of contstruction and landscape materials quite often.

My goal for my buildup has always been tow/haul related but with a decent highway setup.

Often stated in threads about gear changes is the "it may even help your mpg for city/highway" comment based upon the increase in rpm range associated with the lower gears.

My point is --- almost always I read "IT MAY" but rarely have I seen "IT DID". No offense to those who suppose a change should occur but:

How many actual gear changers on here noticed a better (or no change) mpg by swapping out their 3.55's? Doesn't matter if you went to 3.92, 4.10 or 4.56. What are the "REAL" mpg affects of your gear change?

 

honestly, the MPG doesn't even matter. the change is going to run you hundreds of dollars, the minor change in mpg you will see (expect about 1-2 mpg in the city) won't hardly do anything to make your money back. if you drove 1500 miles a month and had a 2wd it would still take you 3-4 years to make your money back!

on the other hand, going to 4.10s from 3.55 if you are hauling and towing all the time, and mostly city driving, you will love the new gears.

 

I have looked into gears as well not for a mpg increase but for a little better acceleration just because I am a freakin speed demon. I have the 3.92's right now. I have heard that switching to 4.10's won't do much but I have heard that 4.56's can actually hurt your mileage on highway. Mileage is bad enough for me as is so idk. Sorry for the thread jack but I don't like starting up new threads all the time.

 

Why is everyone under the impression that 4.56's will hurt highway mileage? They dont. The hemi makes the best mpg around 2200 rpms give or take, cruising at 70mph without the gears I was sitting right at 2000rpms, with the gears I was sitting right at 2200rpms. Personally with the 4.56's installed I saw gains on BOTH the city and highway mileage.

Now I would not do this mod for just mileage as it has been stated above, it doesn't pay you back very fast at all. However they allow the truck to get up to speed faster, they make the engine work less. I do not tow so I cant tell you if they will make a difference there, but passing power is definitely there.

 

Thanks for the info, I am really going to look into these now. I love to occasionally top out my truck and those would make it much more fun and be quicker getting there. Less chance for the cops to catch me accelerating.

 

Truckin151 is hittin close to the head of the nail!!!

I wouldn't change for gas mileage in attempt to get money back. But why would I make a change that makes a poor situation worse?

I have a 4.7L w/manual transmission. I would like better towing performance when I do tow or haul large loads. BUT ... if going to 4.10 gears is going to cause worse mileage in most situations, then I need to re-evaluate things.

Currently, I can/have towed 5K-6K loads around Louisiana, throught Texas (North) and Oklahoma central. I keep the tranny in 4th and turn about 2400 to make 60-65. The real killer is the hilly stuff where I have to dump down to 3rd which is a big rpm jump. 4.10 would give me a better rpm range to work with in 4th. This is all gas mileage killer ...

I know that for strictly performance the 4.10 would be the upgrade to make AND if things are as Truckin151 has experienced, I view it as money well spent.

I really want to hear from those who actually have made a change and what did you note about your mpg.

 

Comment about my earlier post ...

I should say "I really want the opinion/experience" of those who actually made the change and what did you note about your mpg.

Don't want to come off as a snob @#$

 

I went to 4.10 gears and I don't regret it one bit. At first I noticed a slight MPG loss but after a couple of weeks it was back to normal. Its well worth the extra power comming out of the hole IMHO.

 

I went from 3.21s to 4.10s. On the highway, I noticed about a 400rpm difference. Mileage has not really changed....I am still around 17mpg average.

I do have better punch off the line, and I never worried about mileage anyway!

It is a good upgrade.

 

I had 3.92's and went to 4.56's, which is about the same as 3.55 to 4.10. I haven't noticed really much change in my mileage. I was getting around 12 mpg (combined city/hwy, about the same ratio as you, 60/40) with the 3.92's, and I'm pretty much getting the same mileage with the 4.56's. But like Truckin said, the power difference is noticable. Acceleration is better, and I've noticed that the trans doesn't search for gears as much as it used to, especially cruising at 40-50 mph.