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Tour Easy: Yet Another Shifter Pulley

Somehow, I think I’m never going to get around to doing a CNC version of this thing, but at least now I have more pictures…

The overall problem comes from the fact that the Tour Easy frame geometry doesn’t match the expectations of the front shifter: the cable bends over a small finger that, on a diamond frame bike, should simply hold it in position. Here’s the finger, with a very early version of the pulley that just holds the cable slightly higher than the normal position, complete with one snapped wire showing that the pulley wasn’t getting the job done:

Front derailleur cable - broken strand

Front derailleur cable with broken strand

The obvious solution involves running the cable over a nice, rounded surface that prevents abrupt bending. The most recent version looks like this:

Shifter pulley installed - left view

Shifter pulley installed – left view

Yes, the end of the cable sticks out over the chain; I haven’t tucked it in yet.

A bit of lathe work produces a 0.42 inch diameter thin brass disk with a 50 mil half-circle trench around it; in retrospect, the diameter of the trench bottom should be 0.42 inch and the OD should be about 0.45 inch. If you have really good parting-off-fu, you can produce a disk with a finished backside right on the lathe, but I had to drill an off-center hole anyway, so I thinned it on the Sherline:

Shifter pulley - thinning

Shifter pulley – thinning

It looks like this after all the thinning:

Shifter pulley - thinned

Shifter pulley – thinned

One flange is wider than the other: the thin flange faces front and gets a bunch of cutouts, the wide flange faces rearward and must support the bitter end of the cable.

I lined it up in the shifter, filed a notch to fit around the shifter finger, scribed the hole location, clamped it down, and drilled the hole:

Shifter pulley - center drilling

Shifter pulley – center drilling

I think the hole could be on-center with the larger disk; now that I’m keeping better notes, I’ll try that next time. If so, then I can drill it on the lathe, part it off to the correct width, and hand-file the backside flat. The general idea is to have the cable pass over the finger, which almost happens with the smaller diameter.

Some tedious hand-filing produces notches that index over the finger and clear some protuberances on the shifter arm. This is the front face of the pulley that sits against the shifter arm, with a 5 mm socket head cap screw for scale:

Shifter pulley with bolt - front face

Shifter pulley with bolt – front face

The rear face has one side of the trench filed away to get the cable out of the trench and around the bolt:

Shifter pulley with bolt - rear face

Shifter pulley with bolt – rear face

Then it looks like this from the right side of the bike:

Shifter pulley installed - right view

Shifter pulley installed – right view

A pleasant morning with some Quality Shop Time…

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  1. #1 by cole griesemer on 2013-08-11 - 14:10

    I always think your blog is awesome, then comes the occasional bike love post and I’m reminded that it’s actually the best blog ever!

    With the previous cable breakage prevention post in mind, afaik there’s no high/low pull, just top/bottom pull or high/low clamp aka (top/bottom or low swing). There’s also dual pull with a built in cable guide for the “other” direction. I was going to say that since you’re using a friction shifter for the front (despite cross compatibility of sram/shimano for front, mtb and road front derailleurs still have a different actuation ratio) your next derailleur could be a dual pull, but then I realized, at least so it seems, you’d only get the desired cable route with a low clamp, which probably won’t work on your frame. I was also going to say that with a new type of derailleur some other problem would show up, but, well, there you have it. Regardless, your solution is wonderfully elegant anyway, I wouldn’t be surprised to see your idea “borrowed” by a major manufacturer some day.

    Just so you know what you have to look forward to, in the “left view” pic, middle left, the little tab at the bottom of the inner linkage is going to give up its fight against the return spring (hidden under the plastic cover). I occasionally wonder when these huge companies will actually hire a few engineers, but then I remember that the goal is profit, not durability, sustainability, compatibility, or any other of those evil pie in the sky ideas.

    • #2 by Ed on 2013-08-11 - 14:57

      the occasional bike love post

      We like our ‘bents a lot; it’s a rare day when we don’t get out and about on them.

      Today being an exception that we devoted to pulling grass from the Liriope bed out front. While I’m not convinced pulling this grass out of a patch of that grass makes any sense, I agreed to do it until the Liriope gets up and running. [grin]

      afaik there’s no high/low pull, just top/bottom pull or high/low clamp aka (top/bottom or low swing).

      I have no idea what the proper nomenclature might be, having had to deal with only the Old Skool components on the Tour Easy ‘bents for so long. It’s obvious the derailleurs don’t quite fit, though, no matter what they’re called, and the other style wouldn’t work at all.

      Electric shifters, now, that should work…

      the little tab at the bottom of the inner linkage is going to give up

      Although I’ve occasionally replaced front derailleurs, it’s generally due to having the cage wear through; I hope that continues to be the case.

      Thanks for the good words… it’s a fun ride…