3.54 gears vs 3.73

[cervan]

hey everybody, i just bought a 97 f450 dually superduty powerstroke with a dana80 and 4r100 tranny.

Recently im finding that my truck is getting HORRIBLE gas milage since i sit at right about 2800 rpm's to cruise at 70 on the freeway. I dont tow much at all, this is mainly a work truck the most it may ever see is under 3000 pounds on the bed, and maybie 1000 on the hitch. Also im putting a flatbed on the back of the truck to try and get some good MPG out of it.

So my main question is, is 3.54 too tall of a gear that would actually reduce my MPG since i would have to lug the motor more to just pull around the truck? Or would 3.73's be better?

I could also put in 4.10's but i dont think ill ever need a towing capacity that 4.10's would offer, and i may get better gas milage without it. if i go with the 3.73's im going to get the thin gearset for my larger dana80 carrier.

Any input is appriciated.

[late_99_PSD]

I assume since you have a 450 dually that you tow with it. In that case I would want atleast 3.73 gears, if not 4.10's.

What is horrible fuel milage. If its that bad you may want to look elsewhere to find a possible problem.

[cervan]

Originally Posted by late_99_PSD

I assume since you have a 450 dually that you tow with it. In that case I would want atleast 3.73 gears, if not 4.10's.

What is horrible fuel milage. If its that bad you may want to look elsewhere to find a possible problem.

i dont know off hand, but about every 15 miles it eats up 1/8 of the tank ( i dont know the capacity of the tank) but it blows through it pretty quickly. Suprisingly enough i dont see any black/white smoke and the engine oil is pretty clean from what im used to (large 550 cats and detroits). Truck used to have a long start delay, took atleast 15 seconds of cranking before it would fire up, but then it suddenly went away. So im guessing it may be the CPS.

I have a few exhaust leaks that im working on right now, the dreaded up-pipes. i also have feeling that the HPOP isnt producing enough pressure, and the CPS is on the fritz. any other ideas?

To be honest i dont tow a whole lot i got the truck because it was for an absolute steal. I haul more weight on the bed itself than what i tow with it.

[late_99_PSD]

Then I would go with 3.73's. To me they are the ultimate all around gear. Tall enough to still have power, but low enough to get decent fuel economy and have Rpms on the highway.

[cervan]

Originally Posted by late_99_PSD

Then I would go with 3.73's. To me they are the ultimate all around gear. Tall enough to still have power, but low enough to get decent fuel economy and have Rpms on the highway.

cool deal man i appriciate the help. Do you know of a place to get a good used gearset or maybie a cheap new set? ill probibally need bearings as well.

Also, would i happen to have the 35 or 37 spline? or is that something i would have to go out and look for.

[late_99_PSD]

Buying a used gearset is iffy. You have to get the backlash and pinion depth 100% exactly set to what it was in its original housing. If not the gears will wear out very prematurely. You may be better off just saving yourself the hassle and get a new set and a rebuild kit. As far as the best place to get parts I have no Idea. You may want to look at a Mustang/ camaro/ off roading/ 4x4 forum to see what they have to say, as these people are usually going through gearsets left and right

[cervan]

Originally Posted by late_99_PSD

Buying a used gearset is iffy. You have to get the backlash and pinion depth 100% exactly set to what it was in its original housing. If not the gears will wear out very prematurely. You may be better off just saving yourself the hassle and get a new set and a rebuild kit. As far as the best place to get parts I have no Idea. You may want to look at a Mustang/ camaro/ off roading/ 4x4 forum to see what they have to say, as these people are usually going through gearsets left and right

allright thanks again!

[late_99_PSD]

No problem