ScrewnStLou.
I trusted your math - just didn't want you to think I posted after you because I disagreed.

I was suprised by the numbers because I expected an error (3-4 mph?) in the speedometer and an error (50-150 rpm?) in the tachometer. He had to read his gauges carefully at 70 mph. I also expected some variations in the diameters of tires from various manufacturers. His observed reading of 1900 rpm at 70 mph was only 50 rpm off your calculated value based on a standardized tire size! With all four of those variables involved, I expected the final numbers to be a bit farther apart. Pretty darn close!

 

Guys,
I have a 2001 4x4 Screw that came stock with 3.55 gears. I changed the gears to 4.10 (by myself to save money on install). There are advantages and disadvantages to this gear swap:

Advantages:
• Better acceleration.
• Better Stop-and-Go traffic response.
• Better tow capacity.

Disadvantage:
• Highway Gas mileage dropped by the ratio 3.55/4.10.
• On the 2001 Fords, recalibration of the speedo is not yet possible (aftermarket hasn't caught up yet).

Observation:
Engine RPM increased by about 300rpm at crusing speed (70mph).
At 80mph, I turn 2400rpm with my particular setup which isn't bad.

Overall I really like the performance changes and would do it again. City mileage did not change, but highway mileage did lower although I still get about 15mpg at 70mph which isn't too bad. IMHO, I would not go through the trouble of a gear swap if you only go to 3.73 from 3.55. You wouldn't notice that much change.
GDG

 

GoDogGO,
That's pretty cool that you swapped out the ratio to 4.10ls.
Where did you buy the gear's from ? How much $$$ ?
How long did it take you to do the swap ?
I think these truck's really need a gear selection from the factory.
If I were ordering I would opt for the 4.10 also. (if available).
Sorry about all the ?'s
Later...Mike

 

GoDogGo, thanks a bunch for the info, now I really want to do the swap to the 4.10, but with the 4x4 it is gona cost me a bit more. Also have to wait until I have some $$$$$$ to spend...

Also I was reading in the chip forum that there is a 23 tooth gear to reduce the spedo. By the way how much do you think your speed is off % wise?

 

Found that post mentioning the gear reduction for the F-150s

https://www.f150online.com/forums/sh...threadid=58523

I don't know if these work on all F-150s or not, I guess if you go to your Ford dealer and ask them you can find out that way.

 

There are some calculators for gears, tires, and speedo readings on www.therangerstation.com . They are on the bottom of the page.

If money is tight, you might want to plan ahead.

I agree that it wouldn't be worth it to go from 3.55 to 3.73. In some cases, making a gear change will improve mileage. Your odometer is going to say that you didn't travel as far as you really did, so that will throw you off. With a change of tires size, gears and speedo drive gear, you may end up right where you started. That isn't necesarily a bad thing...

 

FALLSCREW
I used Torq-Line gears from US Gears. Very high quality. Avoid the cheep gears or you will pay for them later. As I recall, the rear 9.75" gears was about $240, and the front 8.8 reverse was $199. Shim kits was about $35 each for the front and rear. The rear swap too one full weekend, and the front took one full weekend plus another evening after work.

dcovell,
For the F-150's newer than 1999, the speedometer and odometer are controlled by the PCM, not by a speedo cable. It is possible to recalibrate the 2000's via a chip, but it is not yet possible to relacibrate the 2001's with a chip since the computer set-up changed significantly from 2000. The aftermarket has not yet caught up to the speedo and odometer recalibration for the F-150 2001's. Believe me I tried. I even got one of those recalibration boxes (electric pulse type). It works great, up until the transmission tries to lock-up the TC in OD at highway speeds. The computer won't allow the TC to lock with the box installed and gets "confused". Somehow the PCM is also reading the engine RPM and comparing it to the Output shaft sensor speed (which the box recalibrates). Anyway, the PCM thinks the transmission is slipping since the RPM's didn't change and won't lock the TC. Thats what the aftermarket has to figure out how to correct.
GDG

 

Wow, sounds like you have done your homework. So now if I was to pay a good mechanic to do this form my 4x4 with good gears. How much do you think it would cost me?

I assume you drive a 4x4 as you replaced a gear in the front, is that correct or is there 3 gears to replace on a 4x4?

Also, gota ask this, can you spin your tires easily on a dry flat street on a strait away?

 

Hi dcovell,
WRT the price to install, the local reputable gear shop (Pyle Brothers) quoted about $600 or so just for the install on the 4x4. However, they can get it out in a day if you schedule a time for the morning. So with parts, it is about $1200 or so plus tax of a 4x4 gear swap to have someone do it. That is one of the reasons I did the install myself, to save money, also for the experience. If you decide to do it yourself, it will cost about another $100 for tools (i.e. pinion bearing breaker, two prong gear puller, micrometer, dial guage) unless you already have them.

Yes, only the gears in the front and rear pumpkins need changing, the transfer case is untouched. Rear gears = 9.75", Front gears =8.8" reverse.

On dry asphalt, the wheels spin pretty good from a dead stop. If I powerbrake on dry asphalt, I can spin the tires all the way through second gear sometimes (thats THROUGH second gear, not TO second gear...lol). On dry rough concrete it is harder to spin the tires. I have to powerbrake to about 1800rpm to break the tires loose. Smooth dry concrete is easier than rough concrete and only a little powerbrake is needed.

Hope this helps
GDG

 

Helps a lot, thanks!!!

Sounds like my next upgrade...

Oh and no I will not do it myself, I am good with computers, but working on a car/truck is another thing. I know my limitations.

Oh and what does this do to the warrenty??? I assume it voids the warrenty on the parts you touch. Dosen't bother me much cause I would probley be putting in better componets than it had in there before anyways.

 

You could contact aFord shop to see if they can install it, without voiding the warranty. Just tell them you want it for better low speed towing capacity.