My 1972 240z has a 280z 5 speed transmission. I am having issues with the bouncing needle on the speedometer and while at that i would like to know if i have the correct pinion gear. I have the black one installed and a used yellow one. WHich is the correct one??

http://datsunzgarage.com/engine/

Midway down Page:

YELLOW is the 16 tooth for the 3.36
BLACK is the 17 tooth for the 3.54
BLUE is the 18 tooth for the 3.70
WHITE is the 19 tooth for the 3.90
RED is the 20 tooth for the 4.11
PURPLE is the 21 tooth for the 4.38

If you have the right teeth for your gear ratio make sure the carrier housing is not slightly rotated away from the flat that the keeper locks into that housing is off center for the gear shaft and if it's slightly rotated the gears don't mesh properly and there may be some slop which causes speedometer bounce

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My 1972 240z has a 280z 5 speed transmission. I am having issues with the bouncing needle on the speedometer and while at that i would like to know if i have the correct pinion gear. I have the black one installed and a used yellow one. WHich is the correct one??

The correct one is determined by your differential ratio. Do you know what you have?
I think a bouncing needle has more to do with the speedo cable or the speedo it self. I would start with removing the cable and checking for tight-bends or rusty cable. Lubricate it well and replace. Make sure the rotating cable is seated and the nut is snug. You may want the connect it to an uninstall speedo before reinstalling let me know if you need one I have several extras you can have.


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