LOL ok sounds kinda odd. I have a 92 f-350, with e4od, and 4.10 rear. I have a parts truck from 87 that has a 3.55 rear, which would be better for me RPM wise.

Is there anything I can do with the rear speed sensor? The truck has rear ABS, but it wont kick in, so im not worried there, im more worried about shifting. My trans is fairly new and works pretty good now, so i dont wanna kill it.

 

4.10 at 1800 RPM in OD with 31" tires = 57 MPH
3.55 at 1800 RPM in OD with 31" tires = 65.8 MPH
235/85-16 tires are close to 31" tall depending on who made them and if they are AT or MT or highway tread.

The 2.71 low gear ratio in the A4OD is about = to second in my 4 speed.
If you tow heavy or haul heavy or are in mountains or plow snow I think the 3.55 may be to fast.
If you just driving the truck mostly on highway then the 3.55 would be great.

With my 4 speed and a 4.02 low gear and 3.55's I want a lower gear to start out in for what I use my truck for. But I also want a higher gear for the highway when I am just commuting or running for parts for work.

With 3.55's you would be able to run 55 MPH in second gear at 3300 RPM, this would be even faster if you have tires bigger than 235/85-16 on the truck.

 

when the ring gear and pinion is changed, it does not affect the speed sensor-speedometer at all if your speed sensor is on the rear end, you should be running 2700rpm's or above at 70 mph with truely 4.10's ON THE SPEEDO-TACH, forget tire size and all that. when the speedo says 70, the rpms will be like 2700 or above, i know that a standard tranny in o.d. runs 2100 at 70 with 3.55's and the same truck-rear end with an e4od will run 2400.. i have never driven a e40d with 4.10's. they are a very uncommon combo.

 

The truck is a chassis cab and a former state highway dept truck. I am dead on 2700 at 70mph. Thats what hurts i use it for daily driving 20 miles on he interstate, and those 4.10 kill me. Towing is ok because i never leave OD, on the interstate. and i can only get to about 55 mph in 3rd gear at say 2500rpm.

Truck gets about 10-11 mpg, and i think the 3.55 would be better suited for me.

 

I have a zf5 in mine and I run 3.55's with 305/16's and the truck will run down the interstate 70mph at 2000 rpm.I get anywhere from 17-20 mpg depending on how hard I push her empty,,when loaded pulling an 8,000 lb travel trailer its all I can do to get 55mph on the interstate unless its completley flat ground then I have no problem,,I would like to go to 4.10's also but I as well drive my truck daily 105 miles a day to and from work and I will suffer with the lack of pulling power from my 3.55's so when I stop at the fuel station every friday I never have to put over 50.00 in to fill both tanks.I think its pretty nice when you can run 610 miles in a 9,600 lb truck and only spend 50 bucks.If you do your math you will see the scale that dave gave you was correct,he really knows his stuff about these fords.

 

i don't have to do any math because i know. you can put 44" swampers on your truck and the speedo-tach will say 70 mph at 2700 granted you will be running about 120 mph in real life, but that's beside the point. and shadowcaster, i like the 3.55's for towing also because these trucks have more torque at lower rpm's and will tow much better. when you say you can barely hit 55, this sounds like you are trying to run it as hard as it will go in 4th gear. i could be wrong on this, but if you are trying to get all you can out of it in 4th, try putting it in 5th and easing up on the throttle. it may take a little while to get there,but you will probably get another 10 m.p.h. out of it easy. just from my experience, i want to switch my truck to 3.55's because i think it would pull a trailer a lot easier. i have another identicle truck, but with 3.55's and i can tow the same trailer 65 with 4.10's or 75+ with 3.55's in 5th gear on both trucks. 4.10's just run out of rpm's while towing.(contrary to what most people think) and mostly because they mash the pedal too far to the floor. think what you want, but i have been there done that in 2 identicle trucks accept for the ring gear and pinion.

 

that is in 5th with just over half throttle,,im not out to run 75 80 mph with a load, 55-60 suits me just fine.I was just trying to give him an idea in the fuel dept.I can run up to 70-75 in 5th on flat ground loaded but as soon as I hit the slightest incline she falls on her face with the 3.55's,but also as you stated my low end pull is real good and i like that very much.

 

[QUOTE=89ford73] when you say you can barely hit 55, this sounds like you are trying to run it as hard as it will go in 4th gear. ]
ok, i was worng about this. its just a very common misconception that 4.10's pull so much better than 3.55's 4.10's is only for people who use granny low all the time and don't have 4x4. backing up trailers and dragging them through mudholes, snowplows, stuff like that. or if you want to try to turn your ford into a racehorse and want the tire smoking ratio of 1st gear. when towing, and you think you need a 4.10 gear ratio, just drop a gear, it's very close to the same ratio, then when things get better for ya, go back to o.d. 3.55's is the way to go. if i was you, csramsey, i would use the same rear end housing on the truck and swap the ring gear and pinion only, it would not disturb the speedometer at all. unless you don't care about the speedo, then just swap it all. but it won't smoke the tires out of the hole no more."maybe a little"

 

[QUOTE=89ford73] [QUOTE=89ford73] when you say you can barely hit 55, this sounds like you are trying to run it as hard as it will go in 4th gear.