hi guys, i have my 4.56 install (20 miles on the clock, waiting for 500 break-in) with factory 265/70-17 and my mpg drop from 10 to 7 7-8mpg city what happend?, 4.56 suppose to help on the city mpg right? , is a 03 ram 2500 4x4 nv4500.
tires are to small?, over-geared?.
next on the list is 315/70-17.
but after spending almost 2k on re-gear is driving me crazy?
i only notice from 3.73 to 4.56 small get up and go.
i guess have to wait till break in is over for notice the mpg and power?
let me know what u thinks guy's

 

I believe we covered this same question in your last thread...

 

yes,nothing wrong from getting other opinions right?, thx anyway.

 

Almost everyone reports increased fuel economy in city driving conditions when going to numerically larger gears and this makes perfect sense. You rev at higher RPMs with less throttle pressure, so the stop and go doesn't require as much gas. Obviously highway MPGs can take a small hit as you are revving at higher RPMs at a given speed, although having in essence two overdrive gears (545rfe) will pretty much equalize the effect on the highway.

It's pretty much against the laws of physics not to get better gas mileage in the city if all factors remain the same. Could very well be that you are on the gas a little more wanting to feel the power of the taller gearing (and trying to justify the expense of re-gearing). A lot of times I see guys "on it" without even realizing it.

If you can't feel a boost in going from 3.73s to 4.56s then something is wrong - possibly your butt dyno needs a recalibration, LOL. In going from 3.92s to 4.56s (smaller change than you) it was obvious day/night difference even before break-in was over and I could really get on it.

That said, re-gearing solely for MPG gains is just down right wrong. It's done for low end grunt, for a number of reasons. Towing/hauling, larger tires and faster launch at the track. City MPG gains are minimal and in no way can justify the expense.

In any case, get your break-in period done and drive accordingly. Get the break-in fluid changed and go with a full synthetic and then see where you are...

 

Thanks Hammer for coming and explaining this in better detail than I could, I was trying to explain this to him yesterday but was having a hard time wording it correctly and also explaining that a lot of people regear to gain power and be faster so they usually gas it a lot to feel the increase causing lower MPGs

 

as far feeling a difference, yes the truck feels i little lighter, as for get on the gas i'm pretty light on it, trying to do the break in nice and easy, i never change gear after 3k rpm, always under 3k rpm, yes i want low end grunt!!, but seems a small gain for a almost 2k spending?, as far mpg my top mpg reader before on the city was 9.5 to 11mpg and now is showing 7 to 8mpg, eventually i'm going with 315/70-17 n see if makes a difference, but is like you said have to wait for break-in, i know that 265/70-17 and 4.56 are over-geared, thats why what to go with 35 so can healp me lower the rpm and still get the low end grunt ,and mpg with 35 will be a bonus.

 

$2k is crazy high, my local shop charges $600 per axle for gears, install kit, fluids and install. I believe 3/4 ton axles adds $100 per axle though. I was at $1700 WITH the Auburn LSD & tax.

But anyhoo, yeah you are running the same size tires (basically 31.5" x 10.5") I run on my Grand Cherokee (daily driver, mid size SUV) so you are without a doubt over-geared right now.

 

was $1890 for all with new bearings and seal, don't need new lsd as the 2500 have like a true-trac, yes the tires are to small thats why i'm going with 35 so my mpg will get back up, getting the break-in is hard!!! as u can't get on it!!!, thx

 

Yep, I don't really know that a worm gear LSD functions any better than a clutch LSD, but just about ANY LSD functions better than the clutch one in the 1500 rear ends. The AAM in the 3/4 tons is a good unit...

 

u think the 35 will help me with the 4.56??
any con and pro with that set-up?