I will be installing an air locker in my rear dif. real soon. Right now I am running with 3.55's and getting 19.6 mpg. I have considered changing to 373's while I am in there. My question is , how many of you are running 3.73's, and what kind of fuel milage are you getting. Keep in mind, I have no engine mods, yet. I don't want, nor need, 4.11's as I know my milage will drop quite a bit,and I don't do much towing. I drive 42 miles one way to work, so I have to conserve my fuel milage.

 

Go to 3.73 if you are going to stay with stock tires leave it alone.Merv

 

Prolly should stay with your current gear set.. Your fuel milage will suffer if you change to 3.73's or 4.10's...Those 3.54's you have are really a good gear set for fuel milage......Pete

 

I am currently running 285/75's, and getting ready to upgrade to the 315's. The stock tires were 265's. I don't mind a 1-2 mpg drop, it's the 4-5 I don't want. That is why I don't want the 4.10's.

 

I'd stick with the stock 3.55 even with 315s. Lower gears will NOT give you better mileage. When you switch to larger tires, the tires have more rolling resistance which drops mileage. The fact that they are mathematically taller only drops mileage when you don't account for it on paper.

If you lose grunt with the tall tires and tall gears, install some mild bombs.

IMHO, there's never a reason for 3.73 or 4.10s on a CTD that doesn't tow VERY heavy. The new trucks have 3.73 only because the new wheels are taller. The overall gearing is the same (2K rpm @72mph)

Justin

 

I agree - stay 3.54. Unless you are getting into some regular heavy towing you are not going to benefit swapping to lower gears. Anyway you slice it going to larger tires is going to give some degree of mileage drop. If you are concerned about a performance loss, I agree with these guys, a mild bomb or two and you will forget you even have larger tires - not to mention the big smile it will put on your face when you stomp on it!

 

Agree with all above!

My 3.55 works great hauling at 9,000 lbs and have not heard any complaints from those doing light to medium towing with same rear end. Also gives best milage.

RJ

 

Thanks guys. I know my old cheby gasser had the lower gears. It had pretty good power, but the mpg's sucked. I think I will follow the advice, and stay with the 355's. Thanks guys.

 

Hohn ,
What wt. trailer do you concider heavy enough to warant 4.11 gears?

 

I can tell you that I just changed over to 4:10's because I had a problem towing my 17k trailer. I did loose about 3mpg when I did this swap. However, I just installed RV275 injectors and brought it up 4mpg. I am now getting better mileage with 4:10s then I did with my 3:55's. I only wish I had installed them when I had the 3:55's I can only imagine the mileage I would have got. I am currently getting ~21mpg without towing.

 

Rolling resistance increase yes, but it also lowers the cruising RPMs, i changed to 315's w/ my 3.54's and picked up 1.5 mpg because it put my cruising rpms more inline with my overall speeds.

Don't change your gears, 3.73's will only yeild about 100 rpm difference, not worth the investment. As to needing the higher ratio for towing heavy, it helps some, i ran 4.10's for awhile with my loads but overall i liked the rpms and shifts points of the 3.54's with the 35's and pulling my GN i had no knowticable power loss problems with the larger tires and tall gears towing very heavy actually i liked grabbing direct and being able to pull a 8%-10% grade pass at 65-70 with a lighty trailer and still hit fourth and pull 50-55 with a heavy 20000+ trailer.

 

bluepp,,,, anything over 10,000 lbs would be considered heavy.....Pete

 

Where would be the best place to get a different gear set for my 2000 2500? I am pulling a 12k 5th and when I am pulling at 65mph my RPM is around 1700 and I would like to more that up a bit. Also, what type of rear end would I have (without looking it up) (Dana70 or Dana80).

Thanks

 

Look in the glove box, there should be a label on the inside of the door with that info. I PMed you the link to where I was gonna get mine, but have decided to stay with the 555's.

 

)How hard is it to change the ratio. I can rebuild an engine or tranny but I have never worked with a rear end (not that there is anything wrong with that )

BTW Thanks for the link