Road Runner Nest

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.

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

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

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.

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.

I knew I would screw that up

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

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.

Pretty much what Ron M said above.

http://mymopar.com/speedometer.htm