speedometer gear swap

[roadblock69]

I just swapped out my 7 1/4 rear for a 8 3/4. The gearing is 323 suregrip. I'm running 205/70/14 tires with the stock 904 transmission. My speedo is way off showing much faster than my actual speed. Can anyone tell me which speedo gear I should use to get the correct speed and where I can get one? Thanks in advance. The car had 13 inch wheels and 276 gears prior to the swap

 

[Locomotion]

I only have a few speedo pinions, but there is a chart further down in the thread where you can figure the # of teeth you need. You need to measure the height of your rear tires to plug into the chart. The last 2 numbers of the part numbers listed are the # of teeth on that gear.

http://www.forabodiesonly.com/mopar/showthread.php?t=283358&highlight=speedometer

 

[69_340_GTS]

25.3" tire with 3.23 rear end = 33 tooth gear, according to the chart I have. By the way, these gears are the same for all the different Mopar transmissions of the'60s .

 

[Locomotion]

Going by this more detailed chart, it looks like a 4 tooth gear would work. I have one! PM sent.

 

[trapster]

I would note your trip odometer , when you pass a mile marker drive 10 mile markers and note your odometer.

Find out what number gear you have then divide it by 10 and multiply it by the mileage your odo read then round up or down and check ebay for the correct gear.

And bounce that number off of the above chart.

 

[BigBlockMopar]

You don't need a chart to get the right gear.
Just measure with GPS what percentage your speedo is off of your real speed.
Then check the speedogear in the transmission and apply that percentage on the transmission gear.

Say, if your speedometer is showing 15% too fast, get a gear with 15% more teeth than your current one.
Example; orig. 34 teeth gear + 15% = 39 teeth gear.

 

[69_340_GTS]

Going by this more detailed chart, it looks like a 4 tooth gear would work. I have one! PM sent.

I don't know where this chart came from, but it looks like for almost all the combinatons it is off by one tooth compared to the chart that was published by Chrysler in the Dodge Charger/Coronet/Dart 1969 Service Manual that I am looking at. That is where it says 33 tooth for the tire/gear combo the o.p. is asking about.