Does a gear change modifiy speedometer reading?

[treed]

I've got a 3.73 rear end in my car, does this change the speedometer reading? If so, anyone know by what factor?

Thanks

 

[Bill Pemberton Woodhouse]

Yes,but you may have had a speedometer recalibration kit installed if you bought it that way. Some folks didn't do it though, so if you find out you need one, I would contact Collectors Choice ( they are a sponsor on the site ).

 

[Shelby3]

I recently changed from a 3:73 to stock gears. The calibration kit for the 3:73's is still hooked up. My speedo reads 50 mph now when the car is at 60 mph actual.

 

[Bill Pemberton Woodhouse]

Well,heck, sell him your used kit if he needs one.

 

[Ulysses]

A speedo reading of 65 MPH in 4th gear with stock tires will actually be traveling at approximately 53.5 MPH with 3.73.

What ever speed you are reading, multiply by .8231 to get the actual speed.

 

[STUGOTS]

A speedo reading of 65 MPH in 4th gear with stock tires will actually be traveling at approximately 53.5 MPH with 3.73.

What ever speed you are reading, multiply by .8231 to get the actual speed.

I can see the excuse to the cop now...


cop: "do you have any idea how fast I clocked you at?"

me: well if you hold on just 1 second officer (whips out a calcluatpr) and let me multiply by .8231 I should be able to tell ya.

Cop: "seems we got us a smart a$$ in a viper (smash) you also have a tail light out have a nice night"

 

[treed]

Where/how do you hook up a calibration kit? How much?

.8231 x actual speed seems about right. The car feels a little slow when chugging along in traffic...

 

[Ulysses]

You can get them from several Viper vendors. Roe Racing has one for $129.95. 4 wire hookup. It intercepts the signal before it gets to the speedo.

 

[ViperRichRT10]

You certainly want to recalibrate your speedo. Otherwise, you will be racking up miles on your car faster than you really are! Not good!

 

[rcdice]

You certainly want to recalibrate your speedo. Otherwise, you will be racking up miles on your car faster than you really are! Not good!

Hmmmm... brings up a good point. While I would never suggest such a thing, what if the intercepter made the speedo read, say, 50% of actual. Car would only log 1/2 the miles?

Also, does the fact that a car has had a recalc device wired in effect mileage verification with the DMV? ie. when you sell.

 

[treed]

I was under the impression that with some cars the gear that ran the speedo was different from the gear that runs the odometer... Not positive, but in some cases recalibration of the speedo does not require recalibration of the odometer... very good question, however.

 

[Ulysses]

The speedo signal is not geared. It originates from an electrical sensor, fed to the PCM and then forwarded to the speedo. A single signal is used for both the gauge MPH and the odo. The mileage is also kept in the PCM, just in case.

 

[ROCKET62]

I also have the 3:73 gears. Where would the speedo calibration box be located as on occasion - usually after a thorough wash, my speedo will bounce - leading me to believe that there may be a short somewhere?

 

[ViperRichRT10]

It is located on the drivers side, under the hood, just above the cats, in the electrical box protected by the black metal cover. I hope that make sense???

 

[rcdice]

The speedo signal is not geared. It originates from an electrical sensor, fed to the PCM and then forwarded to the speedo. A single signal is used for both the gauge MPH and the odo. The mileage is also kept in the PCM, just in case.

With a gear change, a speedo recalc unit is needed to give the correct odo reading. Does this mean that overtime the odo mileage reading and the PCM mileage reading could differ? I don't fully understand how all this data is gathered and recorded on a "modern" car so I'm asking.

 

[2002_Viper_GTS_ACR]

I have a speedo calibration box, I used for about 2 months, before I figured out 3.55's were over kill.


IF anyone wants to buy it, I'll sell it for $100 bucks, I pay shipping.


Jon

 

[Ulysses]

With a gear change, a speedo recalc unit is needed to give the correct odo reading. Does this mean that overtime the odo mileage reading and the PCM mileage reading could differ? I don't fully understand how all this data is gathered and recorded on a "modern" car so I'm asking.

Most recalibration boxes intercept the signal after the speed sensor and before the PCM. This leads to the speedo and the PCM receiving the same signal. From what I understand, there is always a little difference between the odo reading and the PCM mileage reading anyway. What someone would be looking for in a fraud type situation is a huge difference.

 

[Shelby3]

With a gear change, a speedo recalc unit is needed to give the correct odo reading. Does this mean that overtime the odo mileage reading and the PCM mileage reading could differ? I don't fully understand how all this data is gathered and recorded on a "modern" car so I'm asking.

Most recalibration boxes intercept the signal after the speed sensor and before the PCM. This leads to the speedo and the PCM receiving the same signal. From what I understand, there is always a little difference between the odo reading and the PCM mileage reading anyway. What someone would be looking for in a fraud type situation is a huge difference.

What happens when you change the PCM? Does the mileage stored start from zero?

 

[Ulysses]

What happens when you change the PCM? Does the mileage stored start from zero?

I asked the same question of the Viper tech.

His response:
"It's programmable with a DRB III."

So it doesn't sound completely fool proof.