trying to figure out which speedo pinion i need to acquire for a 71B trans with a 9 tooth shaft gear

 

i have a 3.9 axle, 14" (5-blade star) wheels and currently a white 19 tooth pinion - speedo error "too fast"

 

is there a chart anywhere showing the pinion (cable) output  rpm/1000  for the various tooth options with that 9-tooth drive gear?

 

these pinion gears are common to a range of cars -  240z, 260z, 280zx (1970-1983).  510 (1968-1973).  200SX (from 07/81-07/83)

 

pinions  range from

16 Teeth Gear: 3.36 axle Ratio
17 Teeth Gear: 3.54 Ratio
18 Teeth Gear: 3.70 Ratio
19 Teeth Gear: 3.90 Ratio

 

various cars had 13", 14" and 15" wheels -

 

did all datsuns of the era have the same TPM ratio  - (i.e. turns-per-mile the speedo expects from the speedometer cable) - ???  - or is that another wild card?

 

makes my head hurt

 

i do not know what model ZX my trans originally came out of

The transmissions are all the same internally as far as the speedo gear.  What matters after that is the tire diameter, not the wheel, and the diff ratio.  Are you running low profile tires?  A typical 205-70-14 tire is a little over 25" in diameter.  That's what I have, with a 3.9 diff, and a white gear (I think.  I had to search to find one).  My speedometer is very accurate.

 

http://tire-size-conversion.com/tire-size-calculator/

 

By the way, here's an archived file that used to be available on one of the Z sites.  http://www.oocities.org/inlinestroker/ratio.html

superb link! -

 

 i can figure out my situation - N(driven) = N(drive) x (axle ratio) x  (tire Rev per mile ) / (speedo TPM rating)

  http://www.v8volvo.se/mekartips/artiklar/speedo-gear.html

 

or by using this calculator  http://www.bgsoflex.com/speedo1.html

 

RPM ratio  = Drive/driven x rpm

 

At 1000 engine rpm in 4^th; speedo cable turns

9/19 = 0.474

9/17 = 0.529

9/18 = 0.500

 

T

By the way, here's an archived file that used to be available on one of the Z sites.  http://www.oocities.org/inlinestroker/ratio.html