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:

P1000985

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 disrailigears.co.uk

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.

Vintage Cyclo Shifter and Derailleur How-(Not)-To

French Cyclo Rear Derailleur

After ruining 4 tandem cables and searching the internet in vain for guidance, I think I have now successfully set up the French Cyclo shifter and derailleur on my 1947 Camille Daudon.

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The only catalogs I was able find were these exploded drawings of Cyclo’s British models, which vary somewhat from the French model I was working on.  While the general concept is the same, the British version has cable stops both at the derailleur mechanism as well as at the shifter lever.

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This is the wrong way to do it.

Without the cable stops, one is left to mangle the cable while trying to tension it and ponder wrapping, double wrapping and twisting techniques to make the mechanism line up correctly and shift properly.

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If you enjoy working with tiny tools or are perhaps a clockmaker or camera repairer – this job is for you!  After identifying the basic tiny parts needed – a nipple for the rear derailleur cable, and a “conjoiner” for the shifter, and the related miniature Allen wrenches and screwdrivers – you are ready.

Cyclo cable nipple

Cyclo cable set up

After shifting the bike by hand to the middle gear, this bike’s rear slot landed at about 9 o’clock.  I installed the nipple and then wrapped the cable around twice.  Oh, I forgot to mention that you’ll need to use a tandem cable, cut off the ends, and then put the nipple about at the midpoint.  Once installed, I used a surgical clamp to hold the cable in place.  (Perhaps a surgeon would also enjoy this job.)  Okay, now for the hard part.

French Cyclo shifter set up French Cyclo shifter set up French Cyclo shifter set up

Threading the cables through their guides, you’ll end up with two ends to be “conjoined”.  After that cable fraying process comes the daunting task of figuring out how to loop the cable properly so that the shifter ends up in the right position.  I turned the shifter upside down and backwards, put the “conjoiner” in its slot, and then twisted the cable and threaded the shifter through the twist, and voila~!  The shifter is upright and the slot position looks good – and now it’s time to adjust the tension.

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This turned out to be the more time-consuming and injurious (the now frayed cable ends caused numerous puncture wounds) part of the procedure.  I ended up identifying one of the cables with some blue tape so I could determine which end needed tension.  I put the shifter in various positions during this process to learn whether the tension was right across this 4 speed drive train’s movement.  It was trial and error, lots of the latter.

Cyclo rear cable

One of the things that kept happening as I was adjusting the tension was that the nipple would come out of its slot – even though double wrapped.  I came up with this temporary solution, shown above, of installing a small rubber band attached to the derailleur mount, which helps to keep the cables aligned.  Once the system stretches and the shapes break in, I will adjust the tension again and decide if the rubber band is still necessary.

Whew!  With the shifting now moderately functional, I am looking forward to rebuilding the hubs – or any other job that doesn’t involve tiny tools and puncture wounds.

UPDATE 4/30/14:

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While paging through a copy of a 1956 Le Cycliste magazine I came across this advertisement.  The rear cable is routed through the derailleur spring!  This solves the problem of keeping the cables aligned while shifting through the gears.  I am going to re-route the cables and hopefully that will solve the problem.