Cage tension cam of front mech. What's its function?

[bj]

Shimano front mech m751

Have used many front mechs in the past but have never seen this function. There is a cam, that accepts an allen key, and when rotated it temporarily increases the cage return tension. The cam returns to its original position if allen key pressure removed, so the tension increase is not permanent. Anyone know its function/purpose.

 

[ishaw]

Re:

I'd guess at allowing you to set/test the mech position without having to cable it up?

 

[Woz]

A few 9 speed FDs have this IIRC.

There is no mention of this screw in the user manual to give you a definitive answer, but what it does is increase
the spring tension when you turn it about 180 degrees - enough to dislodge the spring from a small groove. It's not really
a cam offering different positions, just Low or High tension. Out of the box, it is in Low position with an arrow mark upwards.

It's one of those great Shimano pointless features IMHO. Never had the need to fiddle with it, even old and worn FDs
seem to keep enough spring tension. Now if Shimano put a spring tension adjustment on the RD.......