i have a 02 dodge ram with the 5.9L and 3.9 rear end ratio. i dont do any towing and would like to put a highway gear in the rear end to help with the mpg does anyone have any sugestions thanks

 

You could go to 3.55 gearing but IMO it'd be a waste of money. You may gain 1-2 mpg on the interstate topps, but you'll lose at least that much in town. Not worth the expense in re-gearing to what are really less performing gears for the small highway increase they'll provide.

 

It would take way too many miles to just break even. Not worth the kilobuck or so the conversion would cost.

 

i have to replace the rear end anyways cause the rear end humms
so if i have to spend the money. sould i put 3.55 gears or stick with whats in there right now 3.9 gears

 

Wish I had pulling gears instead of the 3.55's

 

I still wouldn't put 3.55s even if I had to buy gears anyway. The only situation where they will not be worse than 3.92s is on dead flat, open highway over about 70 mph. Anything you gain there, you'll give back (and then some) every time you accelerate from a dead stop.

 

3.55's are the wrong way to go... what size wheel/tire are you running? how much highway driving do you do? how fast do you travel? what you may gain with a 3.55 on the highway you will lose in city stop and go driving. 3.92's or 4.10's are ideal gears in general for all around driving...with that said i drive around on 4.56's because i wanted to have fun driving....

 

I absolutely hate my 3:55 gearing. It's a complete dog with them. I am thinking about the 4:10's if anything. Going to the 3:55's is a bad idea............JMO

Aaron

 

4.10s ain't a bad idea with a 5.9 engine, but with the 545rfe transmission that essentially has 2 overdrives, I'd go straight to 4.56s with the 4.7, 5.7 engines...

 

dang man..

this sure is a new spin on gearing..

buy new tires.. taller ones.. overall gear ratio will move downward (numerically) when you put taller tires on it... You'll have to get your speedometer corrected to see the difference when you do the math after filling up- but you'll effectively do the same thing as lowering gears that much.. I'd guess around an inch and a half to two inches overall tire height would drop your gearing to somewhere in the vicinity of running equivalent to 3.30:1 to 3.50:1 rear gears, but that's just a guess.

on the other hand- bone yards are full of 3.55:1 axles.. you could get one cheap. If you're four wheel drive, you gotta do both front and back or you're in for quite a ride the first time you engage 4WD..