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Old 09-23-2012, 10:08 PM   #1
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Speedo way off, just bought it, used car, what could be the issue?

I had just bought a used 2011 v6 auto mustang about a week ago at a nissan dealership. When I go on the highway I notice that the speedo showed I was going 100 when my gps said I was going 80, and when the speedo says I am going like 85 my gps says I am going 60.

So I had brought it to the local Ford dealership, thinking it is probably better to bring it there than the nissan dealership where I bought it. Anyway, the tech said he couldn't find anything wrong. Nothing went wrong with the tests he did, and the computer says it would be going 80 when the speedo says it was going 80, but he did say he noticed other cars still passing him. They didnt have a gps so they didnt know for sure if the speed was off, and unfortunately I didnt own a gps at the time.

The only thing they told me is that maybe someone had changed the gears, and they didnt know for sure if that was it. He said they would have to send it to another department and take apart the car or something to really find out if there was a change. He said since he couldnt "duplicate" my issue (cuz they had no gps) come back if I notice the issue after I prove it using a gps.

Anyway... I am not totally sure what to do...Should I just shrug all this off and use my gps for my speed, I mean I like my car and it drives fine to me,
I mean if the possible gear change or w/e is no big deal and doesnt affect my car other than the speed, I am fine with that.

Or should I really get to the bottom of this and find out if someone had changed the gears, and then if true, complain to the nissan dealership that no one told me this ? I mean the girl who sold me the car didn't seem very knowledgeable about it, and she even compared it to a luxury car and I almost laughed. anyway.

Any input would be greatly appreciated. Thank you guys very much.
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Old 09-23-2012, 10:11 PM   #2
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Re: Speedo way off, just bought it, used car, what could be the issue?

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Originally Posted by mikeownz View Post
I had just bought a used 2011 v6 auto mustang about a week ago at a nissan dealership. When I go on the highway I notice that the speedo showed I was going 100 when my gps said I was going 80, and when the speedo says I am going like 85 my gps says I am going 60.

So I had brought it to the local Ford dealership, thinking it is probably better to bring it there than the nissan dealership where I bought it. Anyway, the tech said he couldn't find anything wrong. Nothing went wrong with the tests he did, and the computer says it would be going 80 when the speedo says it was going 80, but he did say he noticed other cars still passing him. They didnt have a gps so they didnt know for sure if the speed was off, and unfortunately I didnt own a gps at the time.

The only thing they told me is that maybe someone had changed the gears, and they didnt know for sure if that was it. He said they would have to send it to another department and take apart the car or something to really find out if there was a change. He said since he couldnt "duplicate" my issue (cuz they had no gps) come back if I notice the issue after I prove it using a gps.

Anyway... I am not totally sure what to do...Should I just shrug all this off and use my gps for my speed, I mean I like my car and it drives fine to me,
I mean if the possible gear change or w/e is no big deal and doesnt affect my car other than the speed, I am fine with that.

Or should I really get to the bottom of this and find out if someone had changed the gears, and then if true, complain to the nissan dealership that no one told me this ? I mean the girl who sold me the car didn't seem very knowledgeable about it, and she even compared it to a luxury car and I almost laughed. anyway.

Any input would be greatly appreciated. Thank you guys very much.

It's not much, but your tire sizes could be different than stock.
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Old 09-23-2012, 10:15 PM   #3
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Get them to sort it out. That would drive me nuts! I believe there's a way to figure out the size of your final gear without taking it apart? I'm just not sure of the method. It's worth Googling.
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Old 09-23-2012, 10:19 PM   #4
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just spin the rear tire exactly one turn and count the driveshaft rotations. 3 3/4 ds rotations = 3.73
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Old 09-23-2012, 10:28 PM   #5
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Re: Speedo way off, just bought it, used car, what could be the issue?

it's a v6 auto.
it's got 2.73
at least i know mine does.
it's an auto with 2.73 gears
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Old 09-23-2012, 10:33 PM   #6
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Find what it has stock and go from there. Being an auto and v6, it'll have 2.73 in most cases. For the fuel economy. The tire size doesn't affect too much. Just 1-4mph depending in size. My michelins being a brand new tire and one size above my stock and bald radial t/a threw my speedo off by 1.5 mph. That is no big deal looking at the speedo though.

In your case, we are talking 10-20 off. That could be computer or something. I would literally sit the mechanic down in my car and say, "watch this." But that's just me.
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Old 09-23-2012, 10:35 PM   #7
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he said the mechanic said its probably a gear swap. i say check the gear ratio then have it tuned for it.
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Old 09-23-2012, 10:47 PM   #8
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The cop who pulled me over said to go get my speedometer recalibrated since my wheels aren't stuck. Ha!
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Old 09-24-2012, 12:21 AM   #9
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Quote:
Originally Posted by Tatsumake
The cop who pulled me over said to go get my speedometer recalibrated since my wheels aren't stuck. Ha!
Each inch in wheel size change is 2.7% difference. If you are doing 10mph on 17s, and switch to 18s, it will Say 10, but really be 10.27. I use instrumentation for speed, since I put OEM 2013 GT rims on her, stock was 17. So always a 3% increase in speed, and I have to special calculate mpg.

I would go to Nissan. They screwed you on that one, that isn't right.
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Old 09-24-2012, 12:31 AM   #10
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Re: Speedo way off, just bought it, used car, what could be the issue?

Can you find out from the dealer where you bought your car who owned it before you? Maybe that person can give you an idea on what gears you have.
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Old 09-24-2012, 01:25 AM   #11
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Could you use your GPS and and set your cruise control at say 65 according to the gps and make note of the rpm at that speed which should be 6th gear and see if anyone on this forum with different gears than 2.73s is at that same rpm as you at 65 in 6th gear. That should tell you what gears you have and then I believe its just a matter of recalibrating to those gears.
(Note that auto and manual have different ratios I believe so only someone with an auto can tell you if they run the same rpm at 65, this is also assuming your GPS is correct which I have a hard time believing it wouldn't be)
As a rough guess if at 65 you are under 2000 rpm I would say ur speedo is wrong (my manual car w/2.73 is at about 1500-1600 at 65) if you re above 2000rpm I would say you have different gears than 2.73
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Old 09-24-2012, 08:56 AM   #12
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Re: Speedo way off, just bought it, used car, what could be the issue?

I would definitely go back and have the dealer sort out the problem. I mean, 20 mph off is sort of a big deal and would bug me like none other. You knowwww, try the digital speedometer just to see if it's technical or something small is wrong with the gauges. Worth a shot! Check this thread out if you don't know how to do it...

http://www.mustangevolution.com/forum/f356/t312096/
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Old 09-24-2012, 09:10 AM   #13
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Re: Speedo way off, just bought it, used car, what could be the issue?

Ya it sounds like the car has been geared and wasnt calibrated with a tuner. They can fix that easy. That said I would also make sure the factory tune is in the car. I had a friend buy a car that was tuned and did not come with the tuner and it cost him $$$ to have it reflashed. Voided warranty too.
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Old 09-24-2012, 09:19 AM   #14
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Take it back, by law the speedo needs to be within 10%. Yours is not.

To find out your rear gear ratio takes less than 5mins.
Raise the rear
Mark the DS and a wheel with chalk
Make one rotation of the tire and count how many times the mark on the DS comes by.
2.75 times = 2.73
3.33 times = 3.31/3.27
3.5 times = 3.55
3.75 times = 3.73
4.0 times = 4.10

With a friend helping it takes even less time.
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Old 09-24-2012, 09:33 AM   #15
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Re: Speedo way off, just bought it, used car, what could be the issue?

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Originally Posted by deadsp0t View Post
Take it back, by law the speedo needs to be within 10%. Yours is not.

To find out your rear gear ratio takes less than 5mins.
Raise the rear
Mark the DS and a wheel with chalk
Make one rotation of the tire and count how many times the mark on the DS comes by.
2.75 times = 2.73
3.33 times = 3.31/3.27
3.5 times = 3.55
3.75 times = 3.73
4.0 times = 4.10

With a friend helping it takes even less time.
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Old 09-24-2012, 10:04 AM   #16
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Re: Speedo way off, just bought it, used car, what could be the issue?

measure your tire or put in the size it could be that, stock rims? perhaps Nissan put on the wrong size tires when they sold it to you.
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Old 09-24-2012, 10:38 AM   #17
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It's for sure 3.73 gears mine was 20 mph off you have to buy a tuner I drove around like that for a month. I didn't want to put it on cuz I blew my motor. when your going like 80 you will hit the governor it's annoying as hell
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Old 09-24-2012, 11:27 AM   #18
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Re: Speedo way off, just bought it, used car, what could be the issue?

If it is an auto that is no bueno for the tranny as well. Computer controls everything. Shifting, RPM shift pressure etc. If it isnt calibrated it can do damage to the trans.
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Old 09-24-2012, 08:03 PM   #19
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*STATUS UPDATE*

*STATUS UPDATE*
Ok so I called the Nissan dealership I bought the car from. Lady told me to just bring it to the Ford Dealership, even after I explained to her that if someone had changed the gears, the warranty would not cover that. Talked to the manager and he said same thing...bring it to the Ford Dealership...I atleast convinced him to get into contact with the previous owner to see if he had made any changes...we'll see how that goes...

So anyway...I would try that "easy" test of spinning the wheel and seeing how many times the driveshaft turns, but I dont have jack stands soo... I guess I shouldnt risk doing that with just my jack that came with the car right?.... I will probably atleast bring it back to the Ford Dealership and have them do it i guess. Lol they told me they would have to take apart the back of my car or something to figure it out....i guess they didnt know that trick

Also my wheels are the same ones that came with the car, with aluminum coat and all.

Also tried that digital speedometer on car, and it is still very inaccurate, but does match right on with my speedo needle.

So I guess lets say I bring it to the Ford Dealership and they confirm it is a gear change...all I have to do is buy a tuner right and I can fix this? Its that simple? And some of you are saying I pretty much should do this otherwise my tranny may be affected since I drive an auto? So I guess its that or buy back the original 2.73 gears and tell them to install them...which would probably be silly.

Also I dont know if this will help, but I remember now that the mechanic said he looked at rear gear housing and found fresh silica...this may indicate gear swap?

Lol I just don't get if someone had changed the gears why didnt he also tune it then?


Sorry guys for being a noob. I dont know much about cars and expected to buy a car that worked perfectly right off the bat. But I am trying to learn here. Thank you all for your input, it is greatly appreciated!!!
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Old 09-24-2012, 09:02 PM   #20
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Absoutely do not do it with the car jack. In fact. Don't do anything. It is the dealers problem now. The dealer will be able to change the gearing to the right calibration with there software so you wont need a tuner... Unless you want one of course. If they say they need to bring the car back to the original gear for some reason maybe for warranty or whatever you should absolutely not have to lay out a dime. This is the dealers fault that sold you the car and they should foot the bill or give you back your money. A fresh bead of silicone (used to seal the rear differential cover would be a good indication of at least a fluid change or a gear change, problem that was fixed etc... perhaps even a leak.


Personally if they did a gear change prior to you owning the car and you are ok with the gas milage and it doesnt whine or anything bad I would just have them calibrate it and look at it as an upgrade and be happy.

You're welcome. We were all noobs once.
Good luck. keep us posted.
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Old 09-24-2012, 09:30 PM   #21
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He probably returned the computer to stock before selling it.
If that's the case, the dealer can tell that the computer has been flashed ( if its an 11 or up model) and will deny warrant work depending on how much of a d the dealer is
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Old 09-24-2012, 10:26 PM   #22
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I'm more than willing to bet the previous owner had different gears installed. Probably 3.73s from the sound of it. If that's the situation, I'd stay on the Nissan dealership's case about selling you a car that may not even be covered under warranty anymore.
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Old 09-24-2012, 10:42 PM   #23
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Quote:
Originally Posted by UltArc

Each inch in wheel size change is 2.7% difference. If you are doing 10mph on 17s, and switch to 18s, it will Say 10, but really be 10.27. I use instrumentation for speed, since I put OEM 2013 GT rims on her, stock was 17. So always a 3% increase in speed, and I have to special calculate mpg.

I would go to Nissan. They screwed you on that one, that isn't right.
Yeah take it back to the Nissan dealer and complain to the used car manager! They should've checked that before selling it!

---------- Post added at 11:39 PM ---------- Previous post was at 11:38 PM ----------

Quote:
Originally Posted by pwrby4d

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---------- Post added at 11:42 PM ---------- Previous post was at 11:39 PM ----------

Quote:
Originally Posted by pwrby4d
Absoutely do not do it with the car jack. In fact. Don't do anything. It is the dealers problem now. The dealer will be able to change the gearing to the right calibration with there software so you wont need a tuner... Unless you want one of course. If they say they need to bring the car back to the original gear for some reason maybe for warranty or whatever you should absolutely not have to lay out a dime. This is the dealers fault that sold you the car and they should foot the bill or give you back your money. A fresh bead of silicone (used to seal the rear differential cover would be a good indication of at least a fluid change or a gear change, problem that was fixed etc... perhaps even a leak.

Personally if they did a gear change prior to you owning the car and you are ok with the gas milage and it doesnt whine or anything bad I would just have them calibrate it and look at it as an upgrade and be happy.

You're welcome. We were all noobs once.
Good luck. keep us posted.
Quote:
Originally Posted by Florida3.7L
I'm more than willing to bet the previous owner had different gears installed. Probably 3.73s from the sound of it. If that's the situation, I'd stay on the Nissan dealership's case about selling you a car that may not even be covered under warranty anymore.
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