69 Coronet Speedometer Drive Gear

[markbob]

Hey all u mopar gurus....

I recently had my differential rebuilt and the axle seals and bearings replaced....
my issue now is the fact that the 3.23 gears were replaced with 3.55 gears....and the speedometer is reading incorrectly....

does anyone know what size gear I need? How many teeth?

thanks very much,

Mark

 

[themechanic]

Speedo Gear Calculator

That depends on rear tire diameter. Just download the Excel file to calculate. Simple.

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

 

[Cranky]

I have an extra #32 if you're running 27" tires.....

 

[markbob]

Thx for replies boys....

I measured my tire diameter.....it's 25 inches...
this puts me between the 36 and 39 tooth gears.....

is this correct for a 3.55 gear?

thanks,

Mark

 

[AMX364]

The charts get it close, sometimes must add or subtract a tooth for final correction after test drive. Use mile markers on highway for 10 miles and see how close it is. It rarely is completely exact, but can often be live able. If odometer is correct for the most times then the speedometer will be correct. IMHO

 

[brasil]

.. is the diameter 100% confirmed with 25 " diameter ? check it with a tire calculator.. My tires are 245/6015 and this diameter is 26.3 or .6 .... so my gear has to be a 33 tooth gear ( and it works for me ) In your case it can make a difference if the 25 is closer to 26 perhaps ( i.e 25,7/ .8 ) Check it out

Greetings Juergen

 

[Dako]

I have an extra #32 if you're running 27" tires.....

You are referring to someone with a 4spd, correct? Per the charts in the above link someone with an A/T needs a 35 tooth with 27" tires. Actually, it comes up with 34.41, so the nearest size would be 35? I will need to change this when I re-install my 3.55s.

 

[Cranky]

Don't see what difference it makes since the speedometer pinion plugs into the output end of the transmission. The only effect an automatic has is on engine rpm for any given speed because of torque converter slippage. The stick will have a direct couple to the engine so rpm will always be the same. You can put both in neutral and cut the engine and the speedometer is still going to read how fast the drive shaft is turning the output shaft of the trans. So long as you have the right pinion for the rear gears and tire size, then it should be the same for both auto and standard transmissions.