Middle Chainring Auto-Shifting Problem
I have a 1984 Specialized Expedition. I have set it up with more modern parts. Everything is close to running well now except when I am on the middle chainring(36T) and the largest cog in the rear (30T), the chain has a tendency, or inclination to move to the small chainring. It rarely actually makes the jump, but the chain keeps getting out of the middle chainring moving toward the small chain ring. It seems to only to have this problem when on this gear combination. The cassette is new, SRAM 12-30 8-speed, and the front is an older sugino AT triple crankset.
please shed some light on what might be the cause of this.