# Thinking About Swaping Gears In F-150



## Duanesz (Jul 10, 2009)

I have a 03 f-150 that I am towing my 06 25rss with. I now has factory 3.55 rear gears in it. When I tow now in drive its about 2200rpm at 60mph and is a dog. If i run about 70mph the rpm is about 2700rpm and the power level feels better as far a keeping momentum up going up small hills and getting around people on the highway. The guy that I talked to about the gear swap was trying to get me away from 4.10 saying its a pretty steep gear. I have stock size tires 265/75/17s on it now and dont plan on going any bigger. I dont drive the truck on a everyday basis I really only drive it in winter when it snows and towing my camper in the summer. I would like to upgrade my truck to a crew cab in the future but not for 2-3 years most likely. Does anyone know what my rpms will be in drive at 65/70 miles an hour with the two diffrent gear setups. I dont think its worth it cost wise just to goto 3.73 its not that much of a difference. Anyways let the discussion begin.

Thanks
Duane


----------



## battalionchief3 (Jun 27, 2006)

With the info you provided, get the 4:10. With those size tires ( I assume they are not the stock size ) being over sized your drop your gears automatically, taller tires means your spedo is off some and the gears are like 3:40. Not a daily driver is a plus for sure. A 3:73 would not really be worth it, it would help but for the money the 4:10 would be better. I would bet you would be around 2600ish in the rpm range with those new gears.


----------



## Duanesz (Jul 10, 2009)

Yes its the stock size with the fx4 off road package


----------



## puffer (Aug 28, 2008)

Might as well go 4.10. The 5.4 is a dog sad to say.It may hurt your gas mileage but oh well.


----------



## battalionchief3 (Jun 27, 2006)

Duanesz said:


> Yes its the stock size with the fx4 off road package


Copy that...


----------



## fshr4life (Feb 7, 2009)

If your rpms are 2600 at 60mph with your stock rear end, then you would drop to around 2475 with the 3.73 and to around 2250 rpm with the 4.10. That assumes that you're in the same gear running at the same speed on the highway and you don't make any other changes to the truck. It also assumes that your engine can generate the necessary torque at the lower RPMs (you'd have to look at the torque/rpm curve to verify), so it's just a rough estimate, but it gives you an idea of what changes you'd see rpm-wise.

JD


----------



## battalionchief3 (Jun 27, 2006)

fshr4life said:


> If your rpms are 2600 at 60mph with your stock rear end, then you would drop to around 2475 with the 3.73 and to around 2250 rpm with the 4.10. That assumes that you're in the same gear running at the same speed on the highway and you don't make any other changes to the truck. It also assumes that your engine can generate the necessary torque at the lower RPMs (you'd have to look at the torque/rpm curve to verify), so it's just a rough estimate, but it gives you an idea of what changes you'd see rpm-wise.
> 
> JD


Thats backwards. The R's would go up, not down with taller gears.


----------



## puffer (Aug 28, 2008)

battalionchief3 said:


> If your rpms are 2600 at 60mph with your stock rear end, then you would drop to around 2475 with the 3.73 and to around 2250 rpm with the 4.10. That assumes that you're in the same gear running at the same speed on the highway and you don't make any other changes to the truck. It also assumes that your engine can generate the necessary torque at the lower RPMs (you'd have to look at the torque/rpm curve to verify), so it's just a rough estimate, but it gives you an idea of what changes you'd see rpm-wise.
> 
> JD


Thats backwards. The R's would go up, not down with taller gears.
[/quote]

Thats what i was thinking..


----------



## KosinTrouble (Jul 18, 2005)

If it is not an everyday vehicle then go with the 4.10, you wont regret it.

Kos


----------



## Bakerman (May 1, 2007)

You might want to double check that axle ratio you already have...the marketing of the fx4 is 'off road' which should include 3.73 gears, for the low end torque of driving through mud and up hills? Of course different years vary and maybe can be overridden. My 01 expy with 3.55 gears and 17" tires - in overdrive spun 1700 rpm at 60mpg. I had to shut OD off to run at 2000+ rpm for towing. Even then I swapped out for 16" tires to gain a few rpm (waste of money). If you're towing "in drive" at 2200 rpms, you might have 4.10s already...that setup matches my 2500 GMC, which has 4.10s.

Steve.


----------



## fshr4life (Feb 7, 2009)

battalionchief3 said:


> Thats backwards. The R's would go up, not down with taller gears.


Wow! I must have needed some more coffee this morning! You're right, of course, battalionchief. The rpms would go up with a higher torque ratio for the final drive. So, at 60 mph, you would be seeing around 2700 rpms with the 3.73 and 3000 rpms with the 4:10. The previously-listed assumptions still apply.

JD


----------



## bbwb (Apr 4, 2008)

Definitely go with the 4:10's. The rpm difference and changes in gas mileage are negligible.

bbwb


----------



## Duanesz (Jul 10, 2009)

I am not the original owner but I do have the window sticker and it says 3.55 ratio. I am leaning towards the 4.10. I want to get some numbers in as far a speed and rpm what they will be exactly. I have to drive my truck again and take a note pad with me and see what rpm is now at 60-65-70 in drive is.

Duane


----------



## Duanesz (Jul 10, 2009)

Oh ya one more thing how do I get the speedo changed to work with the 4.10s? I know the factory gear went up to 3.73 so will I have to do this in the computer or do I have to change a gear in the speedo sensor.

Duane


----------



## RLP14 (Jun 18, 2009)

Duane,

I'm pulling a 28BHS with a '03 E150 van, 5.4L. I had the gears changed from a 3.55 to 4.10s and don't regret the change one bit. Gas mileage actually improved 1-1.5 mpg in mostly city and rural driving. I never had a chance to measure what the mileage was towing with the 3.55s because I only pulled the trailer home from the dealer (less than 5 miles) plus one "test run" before having the ratio changed. The van cruises easily at 60-65 mph with the overdrive off when pulling the trailer. You can tell the engine is turning faster than before but it doesn't sound like it's winding too tight. There's no tach in my van so I can't really tell what RPM it's really doing while pulling.

On the issue of speedometer recalibration:.....If 4.10s were an available option at the time your truck was built then a Ford dealer can flash the computer to recognize the change. If, like my van, 4.10s were not an option, then you will need to invest in a tuner or electronic calibrator and make the necessary changes. I'm still doing "fast math" while driving (i.e. multiplying indicated speed by .84 to get actual speed). I hope to get that corrected soon.

Let me know if I can be of any help with this project!


----------



## RLP14 (Jun 18, 2009)

Duane,

One quick clarification. The mileage improvement I mentioned was for non-towing. The towing mileage still isn't great but I don't know if it's better or worse since the gear change.


----------



## Duanesz (Jul 10, 2009)

In my last 700mi trip I got between 8.1-8.6mpg towing


----------



## RLP14 (Jun 18, 2009)

Although I have never towed more than 100 miles one-way, I can't say that I've done any better on mileage with the 4.10s than 8-9 mpg.
I don't think you'll see much change in the towing mpg with the 4.10 gears but you will definitely be happy with the difference in the pulling power.


----------



## MJRey (Jan 21, 2005)

If you're going to make a change you might as well go with the 4:10 since the cost is the same no matter what ratio you pick and you'll be much happier with the 4:10.

Now I've heard a wide variety of costs for swapping gears but none of them were cheap and you'll have to do the front and rear differentials. I'm guessing the total cost could be fairly high for an older truck that you might only keep for 2 more years. It might make a lot more sense to take the money your thinking of spending on the new gears and put that towards a new truck. There are still some good deals out there especially on used trucks and you could probably end up with a better setup for a decent price. If you were going to be keeping the current truck longer it might make sense but 2 to 3 years will make it hard to justify unless you can get the work done cheap.


----------



## Scooter (May 9, 2005)

Ok , I'll be the downer here, 
Even with the gear change it's still gonna be a dog. Don't get me wrong I'm a ford guy , but the '03 and '04 150's are awful (I've owned and towed with both) 
The later model fords have improved significantly.

Don't know if the 150 is paid for - but if not , my vote would be save the $$ on the gear change and put a down payment on a F-250 or similar. The $$ you are planning to throw into new gears would make a great down payment. That along with trade in and low financing (some offering 0%) --- it;s a great time to be stepping into a new truck. (right now the deals are even better buying new , than shopping for a good used)

- don't mind me , it's fun spending other peoples money


----------



## battalionchief3 (Jun 27, 2006)

Lots of companys make speedo calibrators. They can flash your computer and you can get extra horsepower too, go to the dealer if its an option and some make a in line kit that has adjustment screws on it to adjust the spedo. Kinda a trial and error thing.


----------



## Duanesz (Jul 10, 2009)

The truck is paid for I dont see a new truck in my future for a while. I am getting a pretty good deal through a guy who does power train stuff for one of the big 2. Before I was quoted $1800 to do front and rear that was a little to much but now the quote is more reasonable.

Duane


----------



## Collinsfam_WY (Nov 9, 2006)

Duanesz said:


> I have a 03 f-150 that I am towing my 06 25rss with. I now has factory 3.55 rear gears in it. When I tow now in drive its about 2200rpm at 60mph and is a dog. If i run about 70mph the rpm is about 2700rpm and the power level feels better as far a keeping momentum up going up small hills and getting around people on the highway. The guy that I talked to about the gear swap was trying to get me away from 4.10 saying its a pretty steep gear. I have stock size tires 265/75/17s on it now and dont plan on going any bigger. I dont drive the truck on a everyday basis I really only drive it in winter when it snows and towing my camper in the summer. I would like to upgrade my truck to a crew cab in the future but not for 2-3 years most likely. Does anyone know what my rpms will be in drive at 65/70 miles an hour with the two diffrent gear setups. I dont think its worth it cost wise just to goto 3.73 its not that much of a difference. Anyways let the discussion begin.
> 
> Thanks
> Duane


Duane - I had an '02 F150 with the 5.4 and 3.55 gears. You have the 2V motor like I did. Yes it is a dog. It was a dog towing our 23RS which is smaller and a bit lighter than your 25RSS. A gear swap will help alot. If you plan on keeping the truck more than 2 years, I would say go for the swap and unquestionably get 4.10 gears. Also - run the stock sized tire like you are now - no larger. That motor with the 4spd trans can use all the gear it can get. I priced out getting a gear swap from a guy who runs a hot rod shop around here and he would do it for $250 but that is with me bringing him the rear end and installing it back into the truck myself. I think alot of dealers charge around 1k to do it.

I dunno but if it were me, I sure would look into getting an '09 with the newer 5.4 and the 6spd trans. That trans really wakes up that combo. Even a used '04-'08 with the 3V motor will be better. Look at the trans code and see if you can get the 4R100 trans instead of the 4R70W which mine (and I would be yours has) came with. The 4R100 will typically be on trucks with the max payload package.

If that is out of the picture for 2 years or longer, you could consider the gear swap or put the cash aside into a new truck downpayment fund, pay into that fund regularly and just "dog it" until you get a new truck. That is what we did. It wasn't fun and we were a bit limited on where we would tow but shoot - it was so worth it.

-CC


----------



## Duanesz (Jul 10, 2009)

I would not say the engine is a dog. The power is just not it the right power band with the 3.55 gear. When the engine rpm get up above 2600rpm it starts to go. I just think this combo is lugging the engine to much. I sure the newer trucks like the 09 f-150 with 320hp and the 6-speed trans are nice but not $40000 worth of nice not. I can remember not to long ago I could have got a diesel crew cab for what their getting for a half ton gas p/u. I work for the auto industry but the prices of these trucks are getting out of hand. Even up dating to a used 150 for me will be around $10000. I could get about 9-10k for my truck then a used 05 will run in the 18-20k this is a crew cab of course.

Duane


----------



## Collinsfam_WY (Nov 9, 2006)

Duane - I agree that is is largely an rpm problem created by the 3.55's and the trans itself. A good while back, I posted a dyno graph of the 2V 5.4 motor that showed both the hp and torque curves. That graph illustrated some suprising info about the 2V 5.4 - it's torque curves are more like a big blocks' than a small block. It is just my opinion but the 5.4 2V motor, at least the one I had in my particular truck, is a dog. I also accept the possibility that mine might have been a bit of a lemon, power wise, as well. I didn't really have any other experiences with 5.4 modulars other than that one I owned so I don't have anything to compare it to. Also - keep in mind that I live at an altitude of 3,300ft. with an air quality that typically measures over 5,000. That hurts any NA motor. Also - I like power though so my perceptions are prolly a bit skewed by a bit of hotrodding I used to do. Hot runs down the 1340 FTW.

Like I said, I would be looking into a gear swap for 4.10's or take that money and put it towards a new(er) truck. Sounds like you are going to hang onto yours for a good while but an '05 SuperCrew can be had for many thousands less than 18-20k around here. I know how it is when you have no truck payment then you consider getting into one. I just did that in December with the Employee Pricing deals but the payment will eat at me until it is done. I don't like 'em.

-CC


----------



## Chief Joseph (Jul 24, 2009)

I have swapped 2 of my trucks from 3.55's to 4.10's. On both of mine, there was no need to flash the computer. It automatically accounts for the new gears. My first was my dodge ram 1500. I went to a local 4x4 shop and it cost me 1200 for both axles. On my Dakota it only cost me 600 since it was only one axle. Trust me, the difference in pulling power is very noticeable. My dakota was a dog and now it pulls like a powerhouse. If you're gonna keep the truck a while, you will notice alot more pulling power.


----------



## AZthunderations (Aug 21, 2008)

Any good shop doing the work will be able to reprogram the computer to correct for the gear change. It can be done by downloading info directly from FORD or other sites. There is a charge for this service. The other way to do it is to purchase a programmer and use it to change computer settings. The good thing about the programmer is that you can also change engine settings to help tow and then reset for economy when not towing. Check into a programmer, some companies will upload a program into your computer to try. It will only last for a certain time and then revert back to stock settings. Kind of a test drive.


----------



## Duanesz (Jul 10, 2009)

I have a scan gage II your are supposed to be able to correct for tire size But I dont know if it will go that much to accommodate the swap from 3.55 to 4.10


----------



## AZthunderations (Aug 21, 2008)

Using the Ford site to download info will only let you use stock configurations of gears and tires. Most programmers will let you change settings for aftermarket gears, tires, intakes, etc. That's how the guys with the lifted trucks running the huge tires and 4.56 and other gears correct the computer.


----------

