Simplex Grand Prix Rear Derailleur

Simplex Grand Prix Dural

Simplex Grand Prix Dural

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.


Simplex 1939 catalogue courtesy of

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.


1939 Simplex (Fonteyn) catalogue, courtesy of

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 Claw

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.

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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.


Simplex shifter


Cable routing


Original housing for the derailleur

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.

7 thoughts on “Simplex Grand Prix Rear Derailleur

  1. Hi Nola, have you tried a breaker bar on the freewheel wrench/tool? Does the cage collide with the low gear sprocket, or is there some type of low-limiter that has reached its extension. Would it help if you removed one of the cogs to turn the 4-speed into a 3-speed?
    I think you have done a fascinating job, so far.
    Hey, if you decide to purchase a new wheel that a 3-speed freewheel can be put onto, I might be interested in purchasing the one that presently has the 4-speed, especially if it is a 27″ rim. You’re doing a great job…The shifter looks great (I hope the Simplex is not as finicky as the similar Cyclo you showed us how to thread. Toodles. Paul

    • These are 1953 650b Mavic alloy rims with Fratelli Brivio hubs, with a no name 4 speed freewheel. Although I have a number of Cyclo/French freewheel removal tools, this freewheel appears to be a one-off. One idea is to have the tool machined by taking it to someone I trust, in this case that would be Brett at Efficient Velo who machined one of my other f/w tools. For leverage I use Park’s long handled tool, to which I can add a long pipe for extra leverage, which fits over the handle. This Simplex Grand Prix is a 3 speed derailleur – it’s total movement is the width of a 3 speed f/w. So, it cannot be modified to work as a 4 speed derailleur. It’s possible that I’ll replace this with a different 4 speed model, we’ll see about that!

  2. Hello Nola, I have had luck removing the upper pulley of these derailleurs by compressing the bell crank so that I could grab the shaft with plastic jawed pliers. A wrench is usually enough to loosen the nut after that, though i have had to use a battery powered driver once.

    Most if not all the Grand Prix Dural are 3 speed. You can use the nice light weight dural arms of these derailleurs with the plunger/cylinder assemblies from Simplex 4 speed grand Tourisme or Rigidex derailleurs.

  3. For removing the freeweel there is a solution, although usually destructive. You dissassemble it, so you can remove the sprocket, then you are left with only the body you can then put in a vise.
    Et voila.

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