I posted here quite a while back and you folks were a big help then. My question is general I guess, but since my truck fits here, I'll ask here. For starters, my truck is a 1997 F350, 4 door, longbed, 4x4 with 198,000 miles. This truck gets worked hard but driven easy if that makes sense. Upgrades:Tymer air intake; 3" mandrel bent downpipe increased to 4", cat removed, open muffler; BD transmission @ 176,000 miles. I can always use more power, and am aware of several things to increase that. My problem is the highway speed rpm. With the factory 4:10 gearing, I'm cruzing 65 @ 2200 rpm with O/D on; 55 @ 2300 rpm O/D off, (trailer pulling). Hasn't really been too much of an issue here in CA, as I live in a rural area without much highway. But I'm looking at moving to Nevada, where the speed limit is 75mph trailer or no. While I'm not looking to pull my trailers at 75, they are heavy enough to drive with the O/D off. Will putting in a higher gear ratio in my rear ends make enough difference to allow me to drop my top end rpms? I know it will require more HP, but thats easy enough. With my current gears, even traveling empty at the speed limit will make my 15mpgs even worse. Ideas?

 

You can tow the the OD on. I would tow 10-12k with OD on.

 

Seems like when I tow with the O/D on, the tranny constantly downshifts at the slightest hill a shoots the rpm through the roof, which is my biggest concern.

 

How heavy do you tow ?

 

I have a 96 F-350 crew cab long bed 2x4 that had 4.10 gears in it. At 70mph it would hug about 2200. I swapped in 3.55 gears and it dropped it to around 1900. Also have the same truck in 4x4 that had the 3.55 gears and with 37s i was running about 1700 rpm at 70mph and when i went to 4.10s it jumped it up to about 1900. So from my experience, which ain't much in these, is it'll change it about 300 rpms between 3.55 and 4.10s

 

My biggest trailer is 10K loaded. But it'll drop out of th O/D with a slight grade with an empty trailer. Take the o/d off and it'll pull 10K over the Siskyou mountains in Northern Ca at 55 without the cruise even popping off.
For the guy who changed gears...worth it?

 

Do you plan on adding power? If so how much?

Just a thought: If you swapped to 3.55's and added a chip I would bet it would drop your rpms and keep you at the same-ish power.

Also, where are you in Cali?

 

Located just East of Marysville in the Sierra foothills. Lived in Redding 20- something years. I do plan some power upgrades, not huge, but am open for suggestions for this problem. I know in the past, sometimes a boost in power helps with economy.

 

I'm happy with it. Got the truck back in its power ban. I didn't notice any decrease in fuel millage, or at least none to speak of. But I also did away with the programer that was on my truck all about the same time. But when it was on there I could tell it had a little better get up and go to it.

 

My boss owns property down in Marysville. Nice area.

There's a few good reads on chips/injectors/etc... Search around a little bit and you'll find more knowledge than you know what to do with .

 

I went from 3.55 to 4.10 and it was a night an day differance. If you have any grades to pull 10k up you won't like the 3.55.

If you want to do a gear swap I'd go 3.73 and get the best of both worlds

 

I've got 4:10's in my rig and had the same issue , high rpms on te highway. The cost of a gear swap seamed a little much for me so I got bigger tires. @ 75mph in at 2300 rpms, and I can still pull a house off the foundation

 

If I leave the gears alone and go the HP route will that stop the downshifting out of o/d so often? Im not talking about with a big load, but with more medium weights, ie: load of hay in the bed, empty trailer, etc. I've gone to 285's for tires already.

 

FWIW. Some interesting things to ponder....

The OD ratio of the Auto is right around the .86 ratio I thought. With 4:10 gears with the trans in OD your effective ratio to the wheels is......3:55. so if you swapped to 3:55's you would never be able to pull in OD as your effective ratio is now 3:08 and you prolly wouldn't be in the torque curve to pull what your pulling even in 3rd.

I suggest more HP, keep the 4:10's and let it shift into OD.

Diesel Rod

 

I found another member on here that wanted my 3.55's and I swapped with him. I wanted the 4.10's for hauling heavy. You're not going to want to gear up pulling heavy. More power will stop the downshifting as much, but you also need to be sure the trans is up to the task.

Speak of the devil. Dieselrod is the one I swapped with.