2nd Gen Non-Engine/Transmission How To Correct Speedometer Readings..... ??

[Katmandu]

How does one correct for Speedometer/Odometer changes when changing gears or different diameter tires on a 2nd Gen ??

 

[Dennis Garrett]

Well, this worked perfectly for me at all speeds. I have a 97, I think things changed a little in 98 1/2, so you might not be able to do this. I pulled the dash trim, & set it aside. Took out the screws that hold the clear bezel and removed it. I took my finger nails, and carefully pulled the speedo needle off. Then I got my GPS unit and took off down the highway. When the GPS said I was travelling exactly 60mph, I carefully pressed the needle back on it's little shaft so it read exactly 60mph. Worked fine, it was easy, & it's deadly accurate at all speeds.

 

[nps]

When you change tire sizes the effect of the change is to introduce a percentage error. 10% error at 10mph is 1 mph. But 10% at 60mph is 6 mph. So the faster you go, the bigger the error is. Changing the needle works to correct an inaccurate spedo, but won't compensate for larger tires.



On a 98 12V I believe you have to change the drive gear to a different tooth count. The newer trucks are dialed in via PCM programming.



My solution to bigger tires was to tape a correction chart under my visor.

 

[Glen Pratt]

On the '98 trucks the speedo reading is taken electronically off the the rear abs sensor. If the tire size is not huge you could have the dealer reflash your ECM for your tire change. If your running something big and you have 4 wheel ABS you would be better off puchasing one of these TruSpeed Speed Sensor Recalibrator from Superlift. Here' the link:http://www.superlift.com/accessories/truspeed.asp . They're about a $175. 00. I tried the Abbott Electronc Ratio Adapter Speedo box that was mentioned years ago on my truck. It did correct the speedo but it kept tripping ABS codes as it was not 4 wheel ABS compatible. They let me return it for a full refund. Jannetty Racing sells them for $139. 95 http://www.jannettyracing.com , or you can contact Abbott Enterprises

http://www.atrol.com . I ended up just living with it.

 

[WDixon27]

whos got em?

I believe you have to change the drive gear to a different tooth count.

 

[nps]

Dealer's got em.

 

[Alphacowboy]

Programming the PCM with a DRB takes a total of maybe 3 mins for a tire size change. ITS EASY! Its pre programed up to 265/75R16 tires, but can go higher if you do it manually. You need the Rotations per mile of the tire you want to run, and the number of teeth on your tone ring. (D80 is 120 teeth) From the DRB tool, you go into the menu for the ABS system, and its under misc, if I remember correctly. You can then select "Other" it will ask you what Axle type, obviously its a Dana. It then asks you for the tone ring tooth count, enter that, it then asks you for the RVPM, you enter that. Which by the way, If I remember correctly, our PCM can handle up to a 52" tire, so I think its safe to say that it will handle any tire you want to throw at it. :-laf



The Revolutions Per Mile of your tire can be found on the tire manufactures website.



And a side note, I have had 2 dealers in my area let me do it, I just pulled into the service bay, they gave me the DRB, and let me go to town, and it didnt cost me anything... dont know if your dealer will let you do this or not, but it is worth a shot. Hell, slip the service manager a 20, and I am sure they would let ya do it.

 

[Katmandu]

I pulled the dash trim, & set it aside. Took out the screws that hold the clear bezel and removed it. I took my finger nails, and carefully pulled the speedo needle off. Then I got my GPS unit and took off down the highway. When the GPS said I was travelling exactly 60mph, I carefully pressed the needle back on it's little shaft so it read exactly 60mph. Worked fine, it was easy, & it's deadly accurate at all speeds.

Hope you realize that doesn't correct the Odometer readings.

 

[Katmandu]

On the '98 trucks the speedo reading is taken electronically off the the rear abs sensor.

Wasn't there a change in Mid-98 when Dodge went to the 24V PCM setup ??

Therefore, the speedometer/odometer readings are changed as follows...

- Pre-98. 5 12 Valves would be governed by the plastic gear swap in the transmission tailhousing

Whereas... .

- Post 98. 5 24 Valvers are governed stictly by the PCM

 

[ChrisWilliams]

Modifying the settings in the PCM would correct the speedometer and odometer, right. What about the trip, average mpg and instant mpg readings on the overhead computer?

 

[Dennis Garrett]

Hope you realize that doesn't correct the Odometer readings.

Yes that's true, but the original post was "How to correct speedomenter readings". To correct the odometer, I had to change the drive gear which was easy too, but it's been so long ago, I can't remember how many teeth the original had, and how many the replacement has. Seems like 31 or 32 maybe. What I did was re-gear until I got the odometer as close as I could get it, then move the needle.

 

[Alphacowboy]

Modifying the settings in the PCM would correct the speedometer and odometer, right. What about the trip, average mpg and instant mpg readings on the overhead computer?

its alot closer, but still a bit off, especially if you run a fueling box.



But I would much rather change the PCM settings than mess with a box that you have to splice wires to get your speed right. Also, I was under the understanding that the 98 trucks came with the Newer version of the PCM regardless if it was a 12v or 24, as the entire interior was upgraded, including the gauge cluster and electronics in the cab.

 

[CumminsPower98]

Alphacowboy is correct, '98 12 valve trucks are the same as the later 24 valves except for the engine. I have an early '98 made 10/'97 and it's speedometer gets its signal from the ABS sensor on the diff. I started out with 33x12. 5x16. 5 tires on the thing and installed the Tru-speed box at that time. I now have 265/75R/16 tire and all I had to do was adjust the screw in the box.

 

[JDKammin]

I had a tru-speed in my 99 V-10. I took it out when I sold the truck. My 96 diesel speedo was changed by gear in the transfer case. I will sell the tru-speed for $125 shipped to your door.

 

[Katmandu]

Alphacowboy is correct, '98 12 valve trucks are the same as the later 24 valves except for the engine. I have an early '98 made 10/'97 and it's speedometer gets its signal from the ABS sensor on the diff. I started out with 33x12. 5x16. 5 tires on the thing and installed the Tru-speed box at that time. I now have 265/75R/16 tire and all I had to do was adjust the screw in the box.

Dude! You have an EXCELLENT website! I spent alot of time reading thru it. You have a real knack for setting it up! I'd didn't see anything about your Tru-Speed box though... . Maybe you could add that in there!

You folks really need to check out CumminsPower98's Truck Mods website!

http://www.mark74.com/ram_modifications.htm

 

[CumminsPower98]

Katmandu, thanks for the nice comments on the web site. I really enjoy informative sites with lots of pictures so I figured I might as well share some of my stuff. It's also fun to put together... I do need to add update/add some stuff though.

 

[DMannon]

Can the PCM flash adjust for a gearing change? If I change my gear set from 4. 10 to 3. 54, will the dealer be able to adjust the speedo for that? Would they be able to do both gear change and tire size change at the same time?



I know that's probably asking a lot at the dealer level... :-laf

 

[Mundgyver]

I have one of these. Works absolutly great.



http://www.atrol.com/era.htm

 

[jrobinson2]

Can the PCM flash adjust for a gearing change? If I change my gear set from 4. 10 to 3. 54, will the dealer be able to adjust the speedo for that? Would they be able to do both gear change and tire size change at the same time?



I know that's probably asking a lot at the dealer level... :-laf

The tone ring in the differential counts axle rotations not driveshaft rotations so no change is necesary with gear changes on '98 and newer.



As for tire size changes, find somone with a Smarty

 

[EBung]

Can the PCM flash adjust for a gearing change? If I change my gear set from 4. 10 to 3. 54, will the dealer be able to adjust the speedo for that? Would they be able to do both gear change and tire size change at the same time?



I know that's probably asking a lot at the dealer level... :-laf

You do not have to recalibrate for a gear swap on your year of truck. The ABS sensor on the ring gear and the Speed sensor calibrate themselves.