Originally Posted by Trakhak

Campagnolo downtube friction shifters were known to be prone to slipping. Ironically, it might have be a consequence of their manufacturing their components to very high standards of precision.

If the problem recurs after you tighten the D ring, one fix is to degrease the threads of the D-ring bolt and then add a drop of blue Loctite to the threads.

Or there's the quick-and-dirty technique I used with my Campy down tube shifters back in the day: I simply grabbed a Vice Grip and crushed the D-ring threads ever so slightly. Works perfectly and appalls the purists as a bonus.

Originally Posted by oneclick

Ironically it is not the high precision, nor necessarily the (control of) manufacture by Campagnolo that is the fault.

The D-ring or other fixing screw will loosen if there is sufficient clearance between the flats on the mounting bosses and the friction washers of the shifter.
In that circumstance the washers and screw will rock back and forth as the shift lever is operated, and gradual loosening is the result.
So yes, some auxilliary methiod of keeping it from moving is required.
In the past I have resorted to taking a punch to part #174 so it is a tighter fit.

This is a design flaw - the better solution to keeping the friction assembly immobile is that used by Simplex et al: an external tab that fits in a slot, the sides of which can be easily squeezed to take up all the clearance.

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