Speedo question

aerodynamic · Post by **aerodynamic** » Sat Sep 08, 2007 3:14 pm

Hey all. I was wondering what was done to speedometers to compensate for the different gear options that were available. My car must have lower gears than the factory 3:55s it should have because my speedometer reads higher than my actual speed. Judging by how it is on the highway (horrible) I'd say it's got closer to 3:90 or even lower. The previous owner raced it and it had nitrous at one time.

fourforty6pac · Post by **fourforty6pac** » Sat Sep 08, 2007 3:54 pm

You have to get the correct speedo gear for the trans.

aerodynamic · Post by **aerodynamic** » Sun Sep 09, 2007 7:34 pm

So, my first step should be to figure out what gears I have. Where can I get the correct speedo gear?

mopar71 · Post by **mopar71** » Sun Sep 09, 2007 9:08 pm

Correct me if I am wrong, but someone told me to jack the car up(rear off the ground).Mark the tire and a mark on the drive shaft.Turn the tire one complete revolution slowlly and count the number of turns the drive shaft makes.Example 1 tire turn and you get 30 on the driveshaft its 3:90.
does that sound right?3:55 would be about 18 on the driveshaft.You might need 2 people to do this.

fourforty6pac · Post by **fourforty6pac** » Sun Sep 09, 2007 11:59 pm

mopar71 wrote:Correct me if I am wrong, but someone told me to jack the car up(rear off the ground).Mark the tire and a mark on the drive shaft.Turn the tire one complete revolution slowlly and count the number of turns the drive shaft makes.Example 1 tire turn and you get 30 on the driveshaft its 3:90.
does that sound right?3:55 would be about 18 on the driveshaft.You might need 2 people to do this.

One revolution of the wheel and just under 4 revs on the driveshaft would be 390:1, just over 4 would be 410:1 and 3 1/2 on the driveshaft would be 355:1 and so on.

mopar71 · Post by **mopar71** » Mon Sep 10, 2007 11:14 am

I knew I would screw that up

Ron_M · Post by **Ron_M** » Mon Sep 10, 2007 12:30 pm

Try here:

http://www.moparts.com/Tech/tech/pages/speedo.html

some of the numbers supercede, and some of them are on backorder.

The Factory Service Manual also has this info

72GY9Runner · Post by **72GY9Runner** » Tue Sep 11, 2007 4:09 pm

Just so you know....
The speedo gears are still available brand new from Chrylser. I was able to cross reference the moparts page numbers to new cross ups at the local dealership. They even had mine in stock.

71Runner · Post by **71Runner** » Wed Sep 19, 2007 12:55 pm

Pretty much what Ron M said above.

http://mymopar.com/speedometer.htm