speedo musings

[abatzis2 at hotmail.com (Michael Abatzis)]

note: original post broken up. see subject "my car is fast again" for more 
exciting speedometer related insights!

1) anyone know how to calibrate a speedo? the mechanism's interesting, for 
those who've never seen it. there is no direct connection, through gears or 
otherwise, between the speedo cable and the needle. the cable runs into a 
metal disk, which spins within, and doesn't actually touch, a (magnetized, i 
assume) metal cup. the cup is connected to the needle, and the whole thing 
is preloaded with a small coil leaf spring (like the kind in a thermostat). 
calibration is (i think) achieved by turning the needle itself, which should 
affect the amount of preload on the metal cup. this seems like it would be 
extrordinarily difficult to calibrate, but hopefully it's something easy 
like "adjust it so the needle JUST returns to the stop when moved". 
otherwise you'd need to do something like "at this rpm, speed should be x 
mph". install speedo, compare, take speedo out, move needle, repeat until 
you get it right. this would be a colossal PITA.
2) the motometer and vdo units are very different. the vdo is much lighter, 
and harder to dissassemble. i couldn't figure out how to get it completely 
apart. the motometer was easy. the gearing systems for the odometer also 
looked different, more than just the difference between plastic and metal 
gears (the motometer has some plastic gears in the mechanism also, btw, 
although these apparently don't break much).

my car is fast! woo woo! as a side note, that screeching when the speedo is 
cold is now gone. i don't know what the hell that was.

-Michael Abatzis
New Orleans!
1988 Scirocco 2L 16v RIP
1987 Scirocco 2L 16v...

_________________________________________________________________
Have fun customizing MSN Messenger — learn how here!  
http://www.msnmessenger-download.com/tracking/reach_customize