These instructions relate to the Shimano Dura-Ace left hand shifter, in the Jagwire holder for the front derailleur.
Due to the fact that the front derailleur has a strong spring, it can be quite hard to shift into the larger chainrings, with the normal bar-end shifters or twist grips. So Shimano in its wisdom has made its Dura-Ace left hand down-bar shift lever with a strong return spring to counter the derailleur return spring. Thus when properly fitted, these levers will give you easier shifting.
However, you MUST pre-tension this spring when fitting the levers, or you may not get enough travel, and worse, when the lever is in the most forward position, it will severely bend the cable, leading to breakage in a very short time! I will attempt to describe this process with pictures.
Fit the washer to the bar-end holder is this position, with the tab pointing to the front of the trike.
Fit lever and pre-tension by rotating stub clockwise until lever "clicks in" to washer. Note this is easier to do when mounted on handle bar! Then fit the cap and retaining tension adjusting screw, while firmly holding the lever against the washer and holder.
This shows the high limit when correctly fitted.
This shows the low limit when correctly fitted. Note that there is a stop in the lever which prevents it going too far forward and breaking the cable.
This is the WRONG way to fit the washer!
Wrong way and no pre-tensioning results in lever going too far forward and braking cable! Plus there is no counter tension to balance the derailleur spring, making shifting harder than it should be.