I changed my rearend from a stock 71 Dart Swinger rearend (I think its 2.71?) to a 3.23 in an 8 3/4 rearend with a 489 pinion

Drive train:

225 > 904 > 3.23 > 205/70R14

As you guessed, my speedometer reads WAY too fast, like 10mph. How can I go about changing this? A new cable I assume?

Thanks in advance.

A different drive gear for the transmission is needed. Divide the current axle ratio (3.23) by the old axle ratio and multiply that by the number of teeth on the existing drive gear and that's the number of teeth needed on the new drive gear.

More accurately you can run a known distance and divide the indicated distance on the odometer by the actual distance and multiply that by the number of teeth on the current drive gear.

_________________
Joshua

I would guess that it needs a 33 tooth... may-be a 34T if the tires measure short for their advertized size.
DD

Sorry but i'm a total newbie at this speedometer thing.
Where can I get the gear? Any autoparts store?

Also, how do I install it? Is it pretty self-explanitory when removing the speedometer cable off the transmission?

On page 228 of the Year One catalog there are 18 different sizes to choose. New they go for 21 bucks, As always this is only a good guess as Doc said. Same sizes from different tire companies may vary as much as a inch or so in hight.

Ive found that often a trans shop will have a coffee can full of them and will give them sometimes free other times just a couple bucks if you ask and go in knowing which one you need. Often they buy up cores of popular transmissions and build them up so when a car comes in they have a unit ready to swap in to get the car back to the customer faster and then reuse the car's orig gear to keep their speedo reading as it was when it came in. Also look in the FSM, most have speedometer gear pinion charts taht tell which gear is needed with what rear end ratio. The way that Joshie suggests is a good way to start also. I believe that some of these may be available from the dealer yet, the last couple times I needed them, they were like $8-$10ish, IIRC.