How foolish would this be?
05-28-20, 01:10 AM
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How foolish would this be?
Unrelated (mostly) to my other effort to replace the spring in a LePree derailleur, and inspired by previous efforts by The Golden Boy (here) and coolkat (here), I've been trying to transplant a 3 pulley cage onto a SunTour Superbe Pro rear derailleur. The Superbe Pro uses the same pulley cage spring mechanism as their 3 pulley derailleurs, so I thought it might work. It bolts on easily enough, but there's a problem. The pivot stop on the body of the Superbe Pro derailleur is about 90 degrees rotated from the stop on the 3 pulley derailleurs, so it stops here (see pivot stop pin in the red circle):
The result is that it doesn't give me the extra chain wrap I need to use a triple crankset.
So, I was thinking about how I could solve this problem. My first idea was to tap another hole in the cage and move the stop pin right next to where it says "3 pulley system". I think that would work, but it would require me to figure out the threading of the stop pin, buy a tap, drill a hole, etc.
Then a second idea came to me. What if I just removed the stop pin. The chain will stop the pulley from folding back too far as long as the chain is engaged. Bad things could happen if I dropped the chain, but possibly(?) not too bad. So I tried it out.
It looks (!) like it's going to work. What could possibly go wrong?
What do you think?
The result is that it doesn't give me the extra chain wrap I need to use a triple crankset.
So, I was thinking about how I could solve this problem. My first idea was to tap another hole in the cage and move the stop pin right next to where it says "3 pulley system". I think that would work, but it would require me to figure out the threading of the stop pin, buy a tap, drill a hole, etc.
Then a second idea came to me. What if I just removed the stop pin. The chain will stop the pulley from folding back too far as long as the chain is engaged. Bad things could happen if I dropped the chain, but possibly(?) not too bad. So I tried it out.
It looks (!) like it's going to work. What could possibly go wrong?
What do you think?
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05-28-20, 01:23 AM
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I think you need to dial it in and go for a test ride, cautiously. 
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05-28-20, 05:13 AM
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IIRC the stop pins/screws are a convenience vs a necessity. Convenient for the original assembler and for the owner while maintaining the bike. During operation it does nothing so, as you know about RD rotation and can accommodate that while removing and installing the wheel and while changing the chain, then you should be fine. "Weight reduction". However check to be sure nothing is damaged if the cage ever pops back (broken chain, fumble fingers while out on the bench, etc). Does the cage hit some other part of the RD hard and damage it or does it catch a finger and damage that? If so, think on that one a bit.
On the RDs I've worked on or overhauled, some cages relax gently after that pin is removed. Others have much stronger torsion springs and can snap back quite smartly. Could even pinch a finger badly in a scissor action. I don't recall one that would "wap" the RD body and damage it. It also depends on how the high limit screw is set.
On the RDs I've worked on or overhauled, some cages relax gently after that pin is removed. Others have much stronger torsion springs and can snap back quite smartly. Could even pinch a finger badly in a scissor action. I don't recall one that would "wap" the RD body and damage it. It also depends on how the high limit screw is set.
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05-28-20, 05:38 AM
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I had a Shimano Deerhead RD in use some time back in which the stop pin had gone missing. As you note, it was all fine as long as I didn’t have to remove the rear wheel, say like when on a long ride and I got a flatted rear tire and putting it all back together was an origami experiment that failed. So, yeah.
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05-28-20, 05:47 AM
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Yeah, rear flats are enough of a problem without compounding it.
05-28-20, 09:52 AM
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It turns out that if I use the chain hanger braze-on, the cage stays put pretty well even with the wheel off.
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05-28-20, 12:53 PM
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You've done it!
05-28-20, 01:08 PM
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...they laughed at Galileo, too. Well, actually they stopped laughing after a time and sent him before the Inquisition. YMMV
...they laughed at Galileo, too. Well, actually they stopped laughing after a time and sent him before the Inquisition. YMMV
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05-28-20, 01:20 PM
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Is it possible to wind the spring another (almost) full turn and use the existing stop screw in order to get the chain wrap you need for your triple? Or is the spring too stiff?
05-28-20, 02:04 PM
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No, the problem isn't spring tension. The problem is that the pin stops the derailleur where it's shown in my first picture regardless of spring tension. You can't even manually move it past that point.
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05-28-20, 02:07 PM
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Spaghetti Legs sent me this picture when I told him what I was doing.
Totally accurate, right down to me beating on this when it wouldn't work and then later hearing grumbling coming from the garage. (OK, that last part isn't entirely true.)
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05-28-20, 02:24 PM
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It doesn't need to be true, it only needs to be repeated over and over and over, and then it'll be enough true.
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05-28-20, 02:59 PM
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It provides extra chain wrap. When the derailleur cage is forward, the third pulley isn't engaged and it acts like a short cage 2 pulley derailleur. When the cage swings back, the third pulley engages to force the chain to cover more distance. A longer cage accomplishes basically the same thing, but this is weirder.
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05-28-20, 05:04 PM
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Three pulleys is 1/3 cooler than two.
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05-28-20, 09:36 PM
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Grant Petersen would say it's 0.333 cooler, because metric.
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05-28-20, 09:39 PM
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05-28-20, 09:53 PM
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05-28-20, 11:08 PM
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Its actually 150% cooler. That’s OK though, I know you’re an English major.
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05-28-20, 11:21 PM
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But that's assuming that a derailleur's coolness is directly proportional to the number of pulleys. I submit that though those three-pulley derailleur's are pretty cool, the S-1 (with only two pulleys) is cooler still.
Well, at least it's weirder.
Last edited by rhm; 05-28-20 at 11:28 PM.
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05-28-20, 11:54 PM
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I think it’s extremely cool and a worthy quarantine project.
Last edited by Dfrost; 05-28-20 at 11:58 PM.
05-29-20, 01:23 AM
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05-29-20, 01:24 AM
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05-29-20, 01:30 AM
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Yeah, that's some next level stuff right there.
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