SIMPLEX SPIDEL SUPER LJ SLJ PX PY 10 rear derailleur Mercier

Finding the correct rear derailleur for a Mercier build often comes down to one component: the SIMPLEX SPIDEL SUPER LJ SLJ PX PY. This is a drivetrain part from the era when French groupsets ran their own geometry and their own shift logic. At 185 grams, it carries the weight you would expect from a piece designed before the age of indexed everything.

Period Drivetrain Positioning

The naming on this unit is itself a piece of history. SIMPLEX ran the SPIDEL programme alongside the SUPER LJ and SLJ lines, and the PX/PY designation places this derailleur in a specific window of production. That matters when you are matching a frame to a groupset. You are not just hanging a part on a hanger. You are completing the system a frame was originally built around.

The photos are an essential part of reading this component. Every surface, pivot and adjustment point is documented before listing, so the buyer sees the exact state of the piece rather than a cleaned-up ideal. If a major flaw such as rust, a crack or a bent part exists, it is stated plainly in the description. Otherwise, only minor cosmetic wear from storage should be expected — faint marks, micro-scratches, the kind of ageing a part earns sitting in a parts bin for decades.

Key specifications

• Masse (en g): 185

For a full drivetrain restoration, you may also want the matching Simplex rear derailleur vintage bicycle Eroica Peugeot Gitane Mercier. If the shift levers on your build are worn or mismatched, the SIMPLEX vintage gear shifters 1970 PX/PY 10 EROICA are a period-appropriate pairing. You can also browse the full Derailleurs category to see what else is currently in stock.