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.

Simplex Bellcrank Derailleurs

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Why did Simplex use a bellcrank on some of its vintage derailleurs?  I pondered this question as I was cleaning and lubricating a Simplex Rigidex derailleur, which was original equipment on this 1953 Follis:


Sadly, I missed my calling as an engineer (I am a CPA in my day job), so I had to research the question of what advantage a bellcrank mechanism would have over a simple direct pull with a cable on the device that moves the derailleur cage.  Fortunately Wikipedia, and of course, Sheldon Brown came to the rescue.

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The Rigidex was one of several models to use a bellcrank, and was the lower end version of the Grand Tourisme model.  Other bellcrank models included the Lux and Gran Prix.

Simplex Grand Tourisme

1954 Simplex Catalog, courtesy of

You can see from the catalog scan above that the shifter cable lies inside the curve of the bell crank, and is anchored below with a screw.  When the shifter cable is engaged, the bellcrank mechanism moves against a pushrod/plunger that is housed inside the cylinder, and it pushes the pulley cage inward toward the wheel hub, moving the chain across the freewheel sprockets.  Since it pushes, instead of pulls, that means that it is a “high normal” derailleur. At rest, the derailleur lands on the smallest rear cog.  Simplex TDF and Record Du Monde derailleurs are “low normal”, with the pull-chain pulling on the coil/plunger to bring the cage away from the freewheel. Interestingly, the Cyclo Standard and Tourist model derailleurs have a dual action shifter, which is never at rest, as there is always the same amount of tension on the shifter regardless of which position it is in, a result of its dual cables (or single cable wrapped around the shifter) which actuate a helicoid to move the cage.  So, I guess you can say that the Cyclo is a “no normal” derailleur.

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Mimicking the effect of limit screws on modern derailleurs, the above nuts (identified with white arrows), can be loosened to allow re-positioning of the mounting bracket, so that the derailleur can shift properly over the particular freewheel installed on the wheel. This derailleur has a cage swing capacity for 4 speeds.  So, this isn’t really a true limit screw adjustment, instead it’s a hub/freewheel adjustment.

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While there are two springs used for this model, only one of them affects the chain slack.  The mounting bracket is rigid, so there’s no arm which can swing under tension. Instead the larger outer spring is attached to a braze-on on the frame, and serves to act as the tension on the jockey (upper) pulley.  The smaller inner spring keeps tension on the plunger/pushrod, allowing it to return back to its resting position when the cable is slack.  This contrasts with Simplex’ TDF and Champion du Monde pull chain derailleurs, which offer swing arm tension as well as pulley tension.  Even though Nivex came out with its far superior parallelogram rear derailleur back in 1938, the breakthrough was slow to catch on, so that even in the 50’s and 60’s many derailleurs lacked the greater shifting effectiveness provided by the transversing arms of a parallelogram.  Even so, having ridden bikes equipped with these old derailleurs, I have found that they work surprisingly well when properly set up.

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Pulleys feature ball bearings – a nice touch.

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Chain must be broken to be removed – unlike the TDF and Record du Monde models.

I had originally thought that this derailleur allowed the chain to be removed intact, as is the case with the Simplex TDF and Record du Monde models which feature open pulleys at the back of the cage.  That’s not the case for this derailleur.  A nice feature, even on this lower end derailleur, are the ball bearings inside each pulley, instead of bushings.

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So, what benefit does the bellcrank offer?  As I learned from my research, a bellcrank increases the mechanical advantage of a linkage, because the angle of the arms changes as the bellcrank is actuated.  Bellcranks are actually still used in bicycle applications, though not as elegantly as this one.  You can find them on Shimano internal gear hubs, among other applications.

Sheldon Brown

Sheldon Brown – R.I.P.

Sheldon Brown had fun illustrating the mechanical advantage of a bellcrank by featuring a bell which is rung by a bellcrank!

Is this mechanical advantage really needed for a rear derailleur system? It may have been helpful on high normal models which pushed the derailleur toward the hub.  It will be interesting to try this derailleur out on the road, but their application is limited to bikes with brazed on fittings, or by using special brackets which are now difficult to find.

A 1953 Follis 650b

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Here is a very pretty 1953 Follis Mixte featuring Nervex lugs, Fratelli Brivio hubs, Mavic 650b rims, a Simplex Juy rear derailleur with 4 speed freewheel, and a number of other nice features.

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Follis was another highly regarded French builder, founded by Joseph Follis in Italy in the early 1900’s. In the 1920’s, the company established its headquarters in Lyon after Mussolini took power. During and after WWII, the Follis company expanded and began building all kinds of bicycles, varying in purpose and price range, many of which were re-branded by other marques.

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Bonjour, Nicole.

This Follis was owned by Nicole Montbarbon, who resided in Bourg, Ain, France. A clearly visible owner’s name tag was a requirement for all French bicycles during this era.  Nicole took good care of her machine.  Even though the finish is very scratched, the bike appears completely intact and all original, possibly even down to the Michelin 650b 44 mm tires, color matched to the white Sufficit grips and rubber block pedals.


Mavic alloy rims.

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White rubber block pedals


Michelin 650B 44 mm tires – heavily cracked sidewalls means they are not safe to ride and should be replaced.


Follis branded Jeay style brakes, nickel plated.

These Follis Jeay-style brakes are a bit nicer design than others I have seen. The inner plate, which pulls up on the caliper arms when the brakes are engaged, has a groove for each arm to travel on, so they stay in adjustment a bit better.


F.B. – Fratelli Brivio hubs.


Nervar crankset

Fratelli Brivio hubs are a nice touch, though the finish is now gone.  F.B. was an Italian component maker who first built hubs for Campagnolo, among others, as well as under their own name.  Nervar cranksets are not as highly sought after as Stronglight and T.A., but can be equally nice.  This one’s finish is pretty bad off, and it probably wouldn’t be worth it to re-chrome it.  Instead, the patina adds to its vintage appeal.


Minimal brazing for the top tube/seat tube attachment. Through the frame cable routing for the rear brake.


Lined lugs.


Brass barrel adjuster for the rear brake.

I have been amazed at the number of different ways a mixte frame can be configured. In this case, the twin sloping top tubes are hand bent at the seat tube attachment, where they are minimally brazed, before travelling back to the rear dropouts. The frame includes pump pegs, double eyelets front, single eyelets rear, and braze-ons for the shifter and dynamo.  However, this particular frame was not built with the highest quality workmanship.  Although the Nervex lugs are fancy, the drop outs are stamped, not forged, and the finish work on the ends is just so-so.  Even so, a cursory examination of the tubes revealed absolutely no dings or dents, just a lot of scratches and lost paint.

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The lighting system looks intact, except for some broken wiring.  The lamps and dynamo are branded SELF.  The lenses and reflectors are not cracked and have a fun art-deco look to them.  Note the yellow front bulb.

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Simplex Juy Bell Crank derailleur

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Rigid chain guard

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Simplex shifter mounted to frame braze-on.

The Simplex rear derailleur is frame mounted.  This model uses a “bell crank” to move the cage. I haven’t worked on this model before, but fortunately catalog scans are available from Disraeli Gears.

Simplex 05-filtered

This derailleur has open pulleys at the back of the cage, allowing you to remove the chain from the derailleur without breaking it, a helpful feature. The chain is a Sedis model Yellorex, which also appears to be original to the bike.

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Luna Model 122B leather saddle.

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Matching leather tool cases.

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Brass wingnuts, branded “L.P.”

I originally acquired this bike as a “donor” – to give me some needed parts for other projects I am working on.  However, given its completeness and classic beauty, I may change my mind and restore it.  Perhaps that would please Nicole, wherever she may be.  Nous verrons!