I am looking at changing the gears in my 2001 f-150 supercrew. Currently I have a 9.75" rearend with 3.55 limited slip gears. I am towing a trailer around 8000 pounds. It does okay on the flat and the freeway, but going up canyons it struggles a bit. I can only go about 40 MPH at about 3000 RPM, because I have to take off the overdrive and only run in third gear. I am thinking of changing the gears to a 4.10 gear ratio. I was wondering if anyone has done this, or if anyone knows what this will do to the overall performance of the truck. Any information would be greatly appreciated.

 

you'll have to have some recalibration done to the module so the abs will still work

 

Hello Fordguy,

First, here is some approximate rpm info. With the stock 3.55 diff at 3000rpm 1st gear=30mph, 2nd=50mph, 3rd=75mph, OD=110mphOnlyDownhill. If you are indeed towing a trailer that weighs 8000lbs you are maxed out and probably in 2nd with the pedal to the metal on those hills. If you want to tow that trailer a lot and not trash your rig I would definitely get 4.56 diff gears. I tow my horses once a month 300-700 miles each way and the 4.56's are great. My little rig is maxed out at 12,400lbs total truck, trailer & horses and if I do put the pedal to the metal the little sucker revs up into the 3500-4000 range where the power is. I tow at 55mph with the cruise on and in OD at 2000rpms. When it hits a hill it downshifts to 3rd and climbs right back to 55 at 2800rpms. I avg 10mpg towing all over CA AZ NV UT. I drive empty only around town and get 12mpg hot rodding it. 0-60 between lights is a blast. More approximate rpm info. With 4.56 diff at 3000rpm 1st=22mph, 2nd=40mph, 3rd=60mph, OD=85mph.

 

4.10s at least...or 4.56 as fasterhorses mentions if you tow a realy heavy load a lot.

The only re-calibration required is for your speedometer so it reads correctly. Since you have a 2001 this can be done with a programmer.
There's nothing that needs to be done for the ABS system or anything else.

Here are my RPM with 4.10s and street-sized tires:
https://www.ford-trucks.com/forums/5...with-pics.html
If I had 4.56 in there, the RPM would be slightly higher (about 10% or so) at any given speed.

 

Thanks to all those who replied to my post. Just a quick update for those who are curious. I just finished swapping out the 3.55 stock gears with 4.56 diff gears. All I can say is HOLLY COW is this thing quick off the line now. Bottom end torque I have seen a very substantial increase. I am turning 33" AT's and I used to get about 14-15 MPG and now with the 4.56 gears in there I am actually getting around 16-17 MPG. I can actually go up hills now without shifting out of OD. What a difference. I hooked up my trailer just for fun, at the bottom end I can't hardly even tell it's back there. Amazing. I highly recommend anyone who pulls much, or just for the summer camping season, it is well worth the money to swap gears for lower range ones. Only one problem doing this though. You have to be careful off the line cause you can break the back end loose very easily, especially on snow and ice.

 

Glad to hear that you like them.

I think many people under-estimate the torque-multiplying effect of shorter gears on these heavy trucks.

Did you re-calibrate your speedo?

 

Pronstar, I did have to recalibrate the speedo, however I did not have to go and get the computer recalibrated. They make a speedo gear to do this, it was about $8.

 

Right on.
I think you can also do it via a programmer on the newer trucks.

Older trucks like mine are only done via the VSS gear, there is no provision to do it electronically.

My buddy is getting 4.56 put into his 2WD F150 on street tires (305/45-22).
He has a Powerworks blower and will have serious traction problems..more so than he has already

 

Cool stuff pronstar. I was thinking about chipping my truck also, what do you think about that ? is there a better chip over another? And do you have to have a powerchip programmed after you buy them, or can you buy them preprogrammed?

 

I'd check the chips/programmers thread. Lots of opinions in there.

I'm not very current on the latest performance chips an which are better/best.
I had to run a complete custom dyno-tune on my setup.

 

Well all i know lots of people opt for the superchips chips like pronstar check the chips/programmers thread even lots of people go with the Edge program and is mighty impressed with how the truck performes after they hook it up all personal preference i dont think any chip is better than another all have ups and downs

 

I have a similar truck but mine is a 2002. Have you had chance to pull with it yet? I ask because I am considering this but I am concerned about the revs in the 70 mph range. I currently can not tow in OD because it hunts. If I can pull OD with the lower gears I think I will be fine otherwise I think my revs will be too high in third gear.

 

These gassers make their power with higher revs, that's the whole reason for going to 4.56's, get the revs up so you can pull a heavy load. If you want power with low revs you gotta go diesel. I have towed in the mountains and against desert head winds for hours at 3000rpms, OD off, cruise at 55mph no problem. Purrs like a sewing machine and I get 9mpg. On the easy stuff in OD at 55mph I get 11mpg.

 

That is where my revs are now freeway driving (no OD). I am not afraid of the revs. I was just looking for a little better performance down low without sacrificing too much at highway speeds. My theory is with the lower gears I will be able to pull OD on the flat expressways and still be in the same neighorhood I am in now.

And for some reason, my towing mpg seems to be worse than others with similar trucks. 7 mpg, it gets tiring only going around 150 miles before you need to start looking for gas stations.

 

Mich800 I am turning 33" tires on my rig. I went with the 4.56 gears because of that fact. If you are turning smaller tires (stock) you might be able to get away with 4.10's. You probably have 3.55's in there right now.?. I pulled my trailer already to see the difference, even though it is winter. It weighs about 8000 pounds, slightly less now because there's no water in it. It pulled like a champ. Off the line is great higher speeds are also great. I am pulling in OD around 70 MPH, for the first time. My RPM's sit around 2700 to 3000 depending on how far in the throttle I am. Fasterhorse is right though, gas engines make their power at higher RPM's, to get low RPM'S and more torque go diesel. If you want pulling torque when towing and daily driver driveability, maybe change your gears with 4.10's and then put a 4 position atlas transfer case in. It will give you the ability to run 2 high or 2 low as well as your standard 4 high and 4 low. They run around $2000 though. That's why I just went with lower gears and I will just deal with the rpm's sitting up there. Hope this helps.