MY SPEEDOMETER READS 10 MPH TOO FAST????

[jpa99acr]

I own a 99 ACR. Every since I bought it in 2002, it seemed the car was going awfully slow for the speedometer, but I thought hey, it's a Viper, maybe this is how they feel. Well about 6 months ago I hooked up a GPS to it (Magellan 700), which shows the speed on it. As soon as I get past 60 MPH, the needle starts to go up faster than the speed readout on the GPS. Once I hit 70 MPH on the GPS, it shows 80 on the speedometer.

I KNOW that the GPS is accurate because I have used it in my other 4 cars, 2 of which are late model. On every other car it is precisely accurate and matches my speedo.

What gives? Sux because I probably have about 6,000 MORE miles on the odometer than actually exist! (car has 39k miles)

 

[C O D Y]

Stock rear end gears?

 

[jpa99acr]

that was the first question i was asked at ringgold dodge, when i bought the car the person who sold it to me said it was stock, but he was the 2nd owner. nothing had been changed that i could tell. naturally the warranty is out or I'd pay $50 and have them take the rear end apart.

 

[jpa99acr]

kind of off topic, but if someone changes to say 3:55 (instead of stock), they have to accept the additional "fake" miles on their odometer? Wow that's ***.

 

[AJT]

No, you get a speedometer calibration box that makes the adjustment. In the old days you got another nylon wheel that went into the trans at the end of speedometer cable that made the adjustment for you

 

[AJT]

I'm no expert but a speed shop could probably put it on a dyno & tell you what gear is in it & install the box for you.

 

[C O D Y]

Have the dealership check the computer. I think the miles are also kept on the computer.

 

[AJT]

Check here:

http://www.roeracing.com/ProductCart/pc/viewPrd.asp?idcategory=29&idproduct=186

Also check Jon at www.parstrack.com

 

[Whoaa GTS]

or you could set up the GPS and record your speed and RPM in a particular gear. Saw a spreadsheet somewhere on here of redline in each gear with a 3.07, 333, 3.55, and 3.73 rearend.

 

[JiPi]

Well, mine reads about 5 MPH less than what my GPS shows.
96RT, stock gears.

 

[99 R/T 10]

You can check your car in the driveway to be sure. Put the rear of the car in the air(jackstands) and with the trans in neutral, rotate the rear wheel one revolution while counting the revolutions the drive shaft makes. If it is a little more than three times, you have stock gears. If it goes about 3.5 times you have 3.45 or 3.55s. My bet is that you have 3.45's given the fact your speedo reads about 12% more than you're actually driving.

 

[rcdice]

If the car has shorter gears, shouldn't the speedo be off at ALL speeds? Not just above 60 mph.

 

[Whoaa GTS]

Yep, and the margin of error would increase with speed as well

 

[Yellow32]

These guys do a great job recalibrating speedos:

http://www.nhspeedometer.com

-J

 

[Fast Viper Dan]

Your speedo's are all to slow , mine say's 140 at willow springs.