Simplex Grand Prix Rear Derailleur

I thought I was looking forward to setting up this 1940’s Simplex Grand Prix Dural rear derailleur on the Mercier Meca Dural I have been restoring.  But, like everything else with this project, things didn’t go very well.

With many resources available on the web, including a 1939 Simplex catalogue from disraeligears, plus a different Simplex catalogue I found from Peter Brueggeman, it looked like the technical resources would give me everything I needed to get this derailleur set up properly.

These Simplex bell crank actuated derailleurs were offered from the 1930’s – 1950’s. Their mechanical function is the same across all the various models: Grand Tourisme, Rigidex, Luxe, Light Tourist, and Grand Prix (the model I am installing).  The only difference among the models is the length of the pulley cage, and the materials used.  The higher end, more lightweight models use “duralumin” – an aluminum alloy, the same stuff blimps are made of – while the lower end models are made from steel.

The Mercier Meca Dural I am working on did not come with a special Simplex dropout, as shown in the 1939 Simplex catalogue.  So, that meant I needed to use “the claw” to mount the derailleur to the chainstay.

This seemingly harmless derailleur mount is actually possessed by Satan.  First of all, the claw did not fit over the threaded cylinder of this Simplex derailleur.  I tried gently pushing it on, but with the resistance I felt, decided not to force it.  Instead, crazily, I decided to disassemble the derailleur so that I could place the claw over the threaded cylinder, avoiding damage to the cylinder threads.  Or so I thought.

The nut at the back of the upper pulley engages the whole cylinder.  But, it was adjusted so tightly against the pulley cone that I could not release the nut.  After hours of experimentation on a different Simplex derailleur of this era (the Rigidex model) I finally found a way to hold the pulley cone with a Campagnolo crank bolt tool wedged against the pulley cage.  Unfortunately, this same technique did not work with the Grand Prix Dural derailleur, because its pulley cones had very small indentations, and any tool I tried could not hold the cone while releasing the nut.

However, one illumination finally hit my brain:  the claw doesn’t require disassembly of the cylinder – instead it is just tapped into place.  After I tried tapping the claw onto the steel Rigidex derailleur I realized this was true.  I never needed to disassemble the derailleur to attach the claw.  Satan at work…

Once I had the claw on the derailleur it was time to mount it to the chain stay.  Of course, it didn’t fit at all.  So, it was necessary to modify the upper steel clamp of the claw’s mounting bracket.  I put the upper portion in my vise and with a wrench, opened it up quite a bit, so that it would fit on my chain stay. Hurray for steel, which is so forgiving. There is a set screw on the upper bracket which is used to keep the bracket from moving sideways under tension.

I decided to use the original shifter housing for this derailleur.  The creamy white color looks nice with my red brake housings, and to my eye looks better than the steel housing which came with this derailleur when I purchased it recently in eBay.

The bell crank of this derailleur houses the set screw for the cable tension.  If you don’t really anchor this down, the cable will move around.  So, the set screw requires a lot of pressure to hold the cable in place.

Yet another issue was the length of the spring which attaches to the upper pulley and a chainstay braze-on.  The supplied spring was too short, so I have modified a small wire from another derailleur, and will adjust this properly once I have determined the correct chain length.

This rear wheel had a 4 speed freewheel which I was unsuccessful at removing. Even after re-spacing the axle to position the freewheel correctly in this bike, I was sad to learn that the rear derailleur I chose for this project is for 3 speeds, not 4.  I was not able to move the derailleur far enough over with the claw adjustment to  just to use the lower 3 gears on this freewheel. So, this bike will be geared higher than I would have liked.

I hope other restorers and enthusiasts continue to share their technical resources – these are invaluable even if the devil is in the details.