<VV> FC pinion shaft gear & odometer

[BobHelt at aol.com]

In a message dated 9/20/2006 11:49:46 AM US Mountain Standard Time,  
dmonasterio at megared.net.mx writes:

I am  playing with my Rampside's speedometer to make it reading Km instead of 
miles  (have several disassemblied GM speedos) but, as a starting point, I 
don't  remember two things:
1.- How many turns on the speedometer  shaft for each mile ?
2.- I remember that the drive gear  pressed on the diff's pinion shaft has 
multiple threading but, don't remember  if 3, 4 or 5 threads. 
This is for doing the necesary math in  choosing gears.

As always... thanks in advance for any  input.

Daniel Monasterio




Hi Daniel,
I don't know just how much help I can be, but here's what I  know.
 
Early model Corvairs (and i believe FCs too) odometers were calibrated for  
1001 cable revs per mile. This resulted, as I remember, in a speedo and odo 
that  was about 5% fast. However, again as I remember, the spyder odo was geared  
differently. I'm not sure how,  just that when I was "repairing" my spyder  
odo (years ago) , the standard gear spun the odo way too fast.
 
The FC's used two different pinion gears with eight threads. A large one  
(1.884 in. diam) was used with 20, 21, and 22 tooth driven gears. The smaller  
pinion gear (1.766 in diam) was used with the 23, 24, 25, and 26 tooth driven  
gears. For application of these different driven gears, see my article printed  
in the Commumique a year ago or so. I don't know exact date. It's also in my  
Corvair Secrets book.
 
Frankly, I'd suggest that you follow Seth's recommendation and look for a  
metric speedo.
 
Good Luck,
Regards,
Bob Helt