mk1 tachometer getting wacky

[SCIROCCO75 at aol.com (SCIROCCO75@aol.com)]

I finally get my 75 mk1 running reliably and suddenly it's winter!  Oh well 
it's a good time to do a paint job.  Anyhow, does anyone know how to fix a 
tachometer in a 75 mk1 that frequently bounces or jumps?  It was very intermittent 
for along time, but has recently become quite distracting.  Since I'm asking 
for advice I'll throw this in, when I changed my transmission from a 4spd to 
5spd, I have tried 3 different speedo cable ends but cannot get my speedo 
accurate.  Thanks for any help. Michael