2nd Gen Non-Engine/Transmission Realibrating speedo

[jmarx82]

My truck speedo is 5 mph off. I took it to the dealer and they said there was nothing they could do with it has far has recalibrating it. I was wondering if anyone knows how to recalibrate the speedo?

 

[ILIANBG]

Doesn't Smarty do that?
Ilian

 

[jeepit]

I think Smarty can do it

 

[JLandry]

jmarx82,



Unless there's something wrong with your truck, adjusting the speedometer is a simple 10 minute job for a knowledgeable dealer using a Chrysler DRBIII Scan Tool. Find another dealer!



Adjustment can also be accomplished yourself using some brands of aftermarket power programmers like the HyperTech's MaxEnergy or their dedicated Speedometer Calibrator.



If you decide to have a dealer do it using a Chrysler DRBIII, tell them to look for the "Set Pinion Factor" under the "ABS - Miscellaneous" menu.



Whatever way you do it, you'll need to know the tire revolutions per mile to assure the highest speedometer accuracy, although the DRBIII will prompt the operator for the axle type and OEM tire size / brand.



To find the revolutions per mile, check the tire manufacturer's web site, or you can calculate it roughly yourself as follows:



Step 1. Measure the circumference of a tire and multiply that by 3. 1416 (Pi).



Step 2. Take 63,360 (inches per mile) and divide it by the number you got in step 1.



A potentially more accurate way is:



Step 1. Mark the bottom of tire sidewall and road surface with chalk.



Step 2. Drive the truck forward so the tire rotates EXACTLY one revolution, then mark the road surface again.



Step 3. Measure the distance between the two marks.



Step 4. Take 63,360 (inches per mile) and divide it by the number you got in step 3.



Good luck,



John L.

 

[JLandry]

jmarx82,



You might also find these web sites helpful:



Tire Size Calculator 1



Tire Size Calculator 2



Regards,



John L.

 

[HBarlow]

jmarx82,

Unless there's something wrong with your truck, adjusting the speedometer is a simple 10 minute job for a knowledgeable dealer using a Chrysler DRBIII Scan Tool. Find another dealer!

Adjustment can also be accomplished yourself using some brands of aftermarket power programmers like the HyperTech's MaxEnergy or their dedicated Speedometer Calibrator.

If you decide to have a dealer do it using a Chrysler DRBIII, tell them to look for the "Set Pinion Factor" under the "ABS - Miscellaneous" menu.

Whatever way you do it, you'll need to know the tire revolutions per mile to assure the highest speedometer accuracy, although the DRBIII will prompt the operator for the axle type and OEM tire size / brand.

To find the revolutions per mile, check the tire manufacturer's web site, or you can calculate it roughly yourself as follows:

Step 1. Measure the circumference of a tire and multiply that by 3. 1416 (Pi).

Step 2. Take 63,360 (inches per mile) and divide it by the number you got in step 1.

A potentially more accurate way is:

Step 1. Mark the bottom of tire sidewall and road surface with chalk.

Step 2. Drive the truck forward so the tire rotates EXACTLY one revolution, then mark the road surface again.

Step 3. Measure the distance between the two marks.

Step 4. Take 63,360 (inches per mile) and divide it by the number you got in step 3.

Good luck,

John L.

John,

That's an excellent post. It should be very helpful for anyone with a need to recalibrate his speedometer.

 

[SSolderitch]

Smarty only asks for tire diameter. It may be better to use rolling radius x 2. Depends what precission you want... radar gun & mpg's, etc.

 

[drag racer]

I have the Hypertech unit, and it only allows for a tire diameter input to the nearest 1/4" increment. I have found this close enough as verified by GPS, I am within 0. 2 mph at 65 mph...

 

[jmarx82]

Thanks for the replys. I personally know the tech at the dealer and he told me he forgot how to do it because he hasn't done it very much, and he hasn't worked on a second gen in a long time. I know its just an excuse, but what are you going to do.

 

[KrisKringle]

Does that mean that if I change the rear gears to 3. 54, I can program the ECM for the new ratio? In addition, my speedo is reading 10 kmh too slow. Can the Snap on scanner also do the programming job? Thanks. Jonathan

 

[JLandry]

Does that mean that if I change the rear gears to 3. 54, I can program the ECM for the new ratio? In addition, my speedo is reading 10 kmh too slow. Can the Snap on scanner also do the programming job? Thanks. Jonathan

Jonathan,



There's no need to recalibrate the speedometer after changing the axle gearing. The speed singnal is taken off the rotation of the rear axle, which doesn't change when the differential gears are changed.



Having said that, if the speedometer is inaccurate now, it'll be the same afterwards.



I can't say if a SnapOn brand device can adjust it.



Jyst an FYI, the speedometer signal is processed by the ABS controller, not the ECM or PCM.



Best regards,



John L.