speedo gear

[moparbob75]

wonder if somebody can help me. the trans in mr 69 rr is out of a late 70s car and had speedo cable that was cut, my cable in car is screw on type, and the trans im usin did not have a screw on fitting was not a screw in type. i had an extra trans unknown year but it had one that my cable would screw onto now my speedo just jumps all over place. any ideas whats goin on?

 

[Meep-Meep]

Did you reinstall the housing in the correct orientation based on how many teeth your gear has? There is a notch that lines up to a dot on the case.

 

[moparbob75]

well i seen what you was talkin about not sure where it goes gears are 3.23 and tires are 275 60 15

 

[TIGwelder]

Look at the pinion. If the part number is on it take the last 2 digits. That's the number of teeth on the gear. If there is no number, look for the pinion by color on the charts online.

Installing -
On the adapter that the pinion goes in and goes into the trans, look at the numbers on it. Align the proper number with the raised dot on the tail housing. Proper number is number of teeth on gear.


Math Involved to figure out proper gear.

Figure out tire circ.
tire circumference = tire diameter X PI(3.14159)

Change needed values in formula.
((63360 / tire circumference) X gear ratio) / 76.3 = number of speedometer gear teeth


Example for your setup -
So you have a 3.23 gear with a 28" tire
28" tire circumference is 87.96452

(( 63360 / 87.96452 ) X 3.23) / 76.3 = 30.4919

So the gear choices are:
2538930(Yellow)
2538931(Green)

 

[moparbob75]

wow thanks that helps a lot very appreciated