Having an odd issue with a bike I'm rebuilding
old hardrock
biopace triple crank
top swing bottom pull derailer
gripshifter w multiclick/friction/trim

all sprockets are shiftable, however the cable pull is highly non linear
such that in order to get good results the indicator marks on gripshifter must be ignored for 2nd sprocket
ie 1 to 2 requires overtwisting the grip past the 2 indicator mark(nearly to 3 mark)
then 2 to 3 shifts with just a click or two of trim position furthur
so, drastically more cable pull is used up going from 1 to 2 than 2 to 3, yet overall travel is correct - shifter indicator marks for 1st and 3rd line up, but not for 2nd

since the gripshifter is essentially friction, with the indexing positions merely being painted on, it works, but the non linear issue is annoying
any ideas what causes it?

thanks



atm my best theory is the elliptical biopace rings force higher than normal FD positioning, leading to the biased shifting response for higher sprockets....