Category: Machine Shop

The little red pointer inside my Tour Easy’s rear SRAM Grip-Shift broke. Back in the old days, this wouldn’t be a problem, as we used friction shifters on the downtube (as we rode to school, uphill, in the snow, both ways) and knew by feel which gear was engaged. But that was then, this is now, and fixing things is what I do anyway.

The pointer turned out to be a thin plastic strip, molded into an L with a domed arch over the pointy end. It simply rests in a slot in the shifter mechanism, held in place by the transparent cover (which, mercifully, came off without dismantling the bike or even removing the cable).

I made a similar replacement from thin red-anodized aluminum, but that didn’t work out at all. The mechanism snaps from one gear to the next at roughly the speed of heat, accelerating the pointer so rapidly that the aluminum deformed. Score one for plastic!

Actually, I made two aluminum pointers. Prototype One vanished into the Sargasso heap in front of the Solvents & Lubricants Shelves at the first upshift; that’s when I discovered just how much snap that shifter applies to the pointer. Made another one, installed the cover, and then discovered it wasn’t going to work.

So I applied some Plastruct solvent adhesive to the broken plastic bits, lined the parts up on my crusty surface plate, applied a bit of gentle pressure overnight, and in the morning had a like-new pointer. It installed just fine and works like the original.

Solvent-bonded plastic is supposed to be just about as strong as the original material. We’ll see just how long this repair lasts…

Pop Quiz: Do you know the first four derivatives of position w.r.t. time?

Answer: Velocity, acceleration, jerk, and snap. You could look it up…

Update: Alas, the repair lasted only about two weeks before failing at the same spot. Some deep rummaging produced a similar (but more thoroughly dead) SRAM shifter. Turns out the pointers are similar, so I salvaged the older one. Ya gotta have stuff… and remember it, too, which is becoming something of a challenge.

I installed a Terracycle Idler on Mary’s Tour Easy when the old chain tensioner wore out. It’s significantly quieter than a double-idler tensioner, but the rear derailleur can barely handle the 11-34 sprocket / 30-42-52 chainring combination.

She likes it, that’s what counts.

Anyhow, while poking around under the bike, I noticed that the idler no longer slid left-to-right on the shaft through the bearing. The bearing itself spun fine, but the shaft… ugh, they should have used stainless steel.

The sliding motion is important, as the idler should self-adjust to the chainline during shifting. I don’t know how long this one has been jammed, but it could contribute to the noises she’s been mentioning of late and that have prompted me to embark on a major maintenance project.

It shined up nicely with a Scotchbrite wheel in the drill press and now looks merely horrible; you can see the copper plating (wrong: see Update below) showing through. I had to hit one end of it with a medium diamond file to knock off an invisible high spot.

I added a bit of lube and reinstalled it; the bearing slides back & forth like it used to, but I have my doubts as to how long this will last. Fairly obviously, the plating is shot.

The next time it fails, I’m sure I’ll wind up trying to turn an exact 0.3125-inch diameter stainless-steel shaft with a polished surface…

Oh, and the three orange retro-reflective strips? The idler turns backwards because it’s on the return side of the chain: it’s rather disconcerting and I figured it’d be fun to highlight it.

Update: The folks at Terracycle say it’s plated zinc over a brass bushing… which (Ah-ha!) explains the corrosion.

The zinc forms an anode against everything else on the bike; nothing is more anodic than zinc. Because the plating has no volume, it turns into a Fizzy at the merest sight of the usual road salt around here.

Unplated brass would be better: more volume, cathodic against steel, anodic but pretty close to stainless, just as slippery. Might tend to wear against the inner bearing race, but I’d expect it to be at least as durable as the plating.

Here’s a pic of the shaft from another Terracycle Idler I had on my TE for a while. While it’s not corroded, it’s worn through to the brass underneath. So maybe the plating isn’t buying much, anyway.

I spent some quality one-on-one shop time with a random hunk o’ stainless hex rod, came up with a good-looking 0.304-inch OD (a nasty bit of overshoot, but I haven’t done any lathe filing in recent memory and forgot how fast it removes metal), and verified that the race will cock-and-jam rather than sliding nicely.

The Terracycle folks will send a replacement shaft; they’re good folks who build quality stuff and stand by their products. I’m obviously abusing the poor thing…

Update: The stainless shaft arrived and is sized for the 6 mm bolt they’re using in new production. When we discussed this, I said it’d be no big deal for me to adapt it to the existing 5 mm bolt. A length of heat-shrink tubing does the deed, as it’s rigidly held on both ends. A dab of Loctite, a dot of oil, and it’s back in service. We’ll see what happens after a few months of riding under my regime of benign neglect.

A tip o’ the cycling helmet to Terracycle!