So I currently have a 2014 v6 with a gear ratio of 2.73 I wanna put in a 3.73 but I wanna make sure I won’t have to change anything else. I’m already making other mods like intake, fuel injectors, driveshaft, and radiator. But I wanna make sure the 3.73 will run fine with the transmission, and engine without a tune.

 

You will need a tune for the Speedometer to be correct.

 

yep the speedometer will be off by the same amount as the gear change, if not corrected with a tuner . . . 3.73/2.73= 1.36; meaning the driveshaft will be turning 36% faster at the same vehicle speed, so the speedometer would read 36% high if not corrected

one other concern if the driveshaft itself -- if you plan on removing the speed limiter, and driving the car at high speeds like over 120 or so, then there have been some problems with exploding driveshafts in the V6, you might want to look in to that

why do you want to change the gears; what are you hoping to get out of it? 2.73 to 3.73 is a huge change; depending on why you are considering it, you might want to consider something in between like 3.31 or maybe 3.55

 

As Bert mentioned, you're looking at a big change, which would mean much higher revs at highway speeds. You'll get some low-end performance for sure, but there's a price to pay at higher speeds. A lot depends on your typical driving.

Not saying don't do it, just making sure you know the costs other than the money-related ones.

 

The Speed info comes from the ABS via tire Rotation. U dont Need to change anything with a tune etc.

 

^ wrong information . . . or is it misinformation? or disinformation? either way, it would be grounds for being cancelled if this was Twitter or Facebook, LOL

 

I will tell you haw wrong you are, when I first got the tunes for my 2013 and gave then the number of the ECU I was under the impression the ECU also knew the gear ratio. My car has the the Performance Package so it has 3.31 gears. They gave me the tunes for the car and they were written for 2.73 gears and not the 3.31. So now you know there is no Speed input from the ABS system to the Speedometer.

 

And what do you think where the speed Info comes…? From Heaven…? The Cluster who Show you your Speed, Takes the speedinfo from the Can Bus. The ABS Module put this Info into the Can Bus. The ABS Takes this Info from the ABS Sensors. The wiring diagrams below shows it. All you Can do, to manipulate the speedinfo, is to change the rev/mile Ratio of your Tires in the ABS module. Than your Cluster will shows you something different. But the rear Axle Ratio has nothing to do with the shown speed in the gauge/cluster.
what you mean is, if the speedinfo is tanken from the transmission like older Mustangs or older Cars, than you are right, because the Info is taken in front of the rear Axle / Driveshaft (before) that needs a retune. But on the 2010-2014 Mustang the speedinfo comes from the ABS Sensors and they are behind the driveshaft and rear axle trans.
I know that the ECM/PCM has programmed the rear axle ratio, and i know that you Can retune that with a maybe sct x4 tuner. But the reason for that are not a wrong shown speed from the gauge/Cluster if you change the rear axle Ratio.

 

wow, that's really weird . . . everyone has been doing it wrong all this time; adjusting rear gear ratios in tuners and seeing the change on the speedometer . . . . I guess that was all hallucination; who knew?

 

no, you doing right if u change / adjust it with a tune, but that has nothing to do with the shown speed.
U Can read the diagrams…? For Example: your tire rotate maybe with 50 km/h the abs Module put this Info into the Can Bus. Now if u change the rear axle Ratio from 2:73 to 4:10 you have a higher Engine rpm with a lower car speed. Just an example: 2:73 / 50km/h 3rd gear 2500 rpm, against 4:10 / 50 km/h 3rd gear 3500 rpm. The Engine rpm are unimportant for shown speed. The ABS measure just the rotating speed of the tires in Booth example. So 50 km/h = 50 km/h measured by Abs and put into the Can Bus. Only difference is the Engine rpm, but that is unimportant for the shown Speed. I Never say that u Not retuned the software, there are other important thinks that must known the rear axle ratio, but for the shown speed, it’s unimportant.

 

was the speedometer wrong when the rear gear ratio was wrong in the tune; and was the speedometer corrected when the gear ratio was corrected?

 

u know what a Original Electrik diagram is…? It can’t lie. So I don’t know what’s wrong with your speedo, all I can say is, look at the diagrams.

 

Nice pretty Diagram, the MT82 Transmission does have an Output Shaft Speed Sensor, it is where the signal for the Speedometer comes from. Shown Speed comes from the OSS on the transmission as well for the audio system, back up camera speed and anything else that is speed related or adjusted by speed. The ABS Module 151-2 is not even connected to anything in the instrument panel except by a connection for the ABS light if it goes bad. So where do I think the Info for the Speed comes from, Item C193 on page 11 of the 2011 Mustang Service and Workshop Manual. The Speedometer does not care what the wheels are doing, it gets told by the Transmission. Case in Point, read said Thread.

Yes sir Bert, all fixed when the 3.31 was inputted and the 2.73 removed

I do know what an Electric Diagram is, in fact I can even spell Electric. You are right though, it cannot lie but the person reading it sure can misunderstand what he is reading.
From what I am reading in the email I got from a friend that actually works as a brake engineer at Ford the ABS sensors read RPM and not speed. That is why when you have your foot on the brakes and your wheels are modulating with the ABS system your speedometer is not unless your rear wheels are locking up. That is also why you still have a speedometer if you disable your ABS system which my question to him originally what was affected if the ABS system was disabled because my Advance Trac kept activating and I was going to pull the plug on it to get home.
So do you want to keep telling me the ABS runs the Speedometer on my Mustang now.
Just so you know the ABS doesn't run the Speedometer in my F150 either, it gets its signal on it from the Lead Frame and the OSS in the transmission. This is why the 2011-14 F150s were recalled since the Lead Frame was picking up metal in the Magnets and causing a no Speed Shown and the transmission would downshift like it was stopped at a light..

 

One more thing, since you think the ABS system tells the Speedometer what the speed is, Car has 255/40 19 on the front, tires are 27.1 inches and you have 295/40 19 on the rear which are 28.3 inches, How in the Hell does your ABS system know which sensor is correct???? There is no way to put 2 tire sizes into the car for Speedometer Calibration and it is not adding it to the ABS system.
Edit. It used to be when you take your V6 into Ford for Speedometer calibration, it is changed at Ford in the V6 by Tire Size (stock Sizes only) and one of the 2 gear ratios available, the 2.73 or the 3.31, GT can have any of the available Gear ratios in the Manual Trans cars and the Stock Tire size. Automatic cars were only able to change tire size and had to use the 3.15 gear ratio since that is all the GT autos came with. They might be able to do more now 7 years later with the Ford IDS system since I know we can with ForScan on the F150.

 

yes, and like he said, I even know how to spell electric

but the person reading it can misunderstand or read more in to the words than what they actually mean . . . to see where the speedometer gets its signal, you need to look at the speedometer logic; not just assume that since there is a sensor called "wheel speed sensor" that is where the speedometer is getting its information

 

When the lead frame in my transmission went bad, the car would downshift to 1st gear without warning when traveling at highway speeds because the transmission speed sensor would tell the computer the car had stopped (the speedometer also dropped to 0). The ABS sensors are NOT used as a speedometer input. They are used during braking, and as part of the traction/stability control system.

 

@SpectreH

SpectreH, I just had a reman transmission put in my 2014 Mustang and had this happen to me where the speedo went to zero on the freeway and the car downshifted to 1st. How did you fix the problem? My car isn’t showing any codes and the mechanic doesn’t know what happened. My tuner put the transmission tune back to stock. I’m afraid of it happening again and causing an accident.

 

You need to plug it in to Ford IDS and look for a P0700 Transmission Fault, P0706: Transmission Range Sensor Circuit Range/Performance or a P0720 code Output Speed Sensor Fault. The ones they use at Autozone do not pick up all codes, transmission codes and ABS codes can be or are in a different computer.

 

For me, it was the lead frame inside the transmission. Ordinarily I would have done the work myself, but was in a hurry and let the dealer replace it. Car ran great after that.