Shimano Derailleur Adjustment for Dummies - The Freelance Files MMCCXXXIV

derailleur barrel adjuster

It is astonishing (though it probably shouldn't be)  to our house bike mechanic that the first step of damned near every eHow.com post purporting to tell people how to adjust the rear derailleur on a bicycle includes some variation on the words "loosen the cable bolt." It's as if all those freelancing morons just copied one another's work, swapping in "Altus" for "Tourney" or "SRAM" for "Shimano." Oddly, it seems as though they all cited a book for their "reference," too. Well, we have a REAL reference, one that's online, and we'll point you to it in a few minutes. But first, let's look at just how clueless one Donovan Gillis proved himself in the SportsRec.com post, "How to Adjust a Shimano Tourney Derailleur."

Gillis, whose bona fides as a bike mechanic consisted of studying martial arts and business management, demonstrated his ignorance of bicycle drivetrains right there in his introduction, when he blithely "informed" his readers that,

"Many commonplace things that occur during riding can cause your derailleur to become misaligned. Bumps and jarring to the bicycle will cause your limit screws to slowly unscrew themselves."

We call bullshit on that. The most common reason indexed derailleurs require fine-tuning is not "unscrewed" limit screws, it's that shift cables stretch as they age. Which, when you think about it, renders Donovan's "step two" (after positioning the bike) completely useless:

"Loosen your cable stops by turning them counterclockwise with an Allen wrench. The cable stop is the bolt on your derailleur that the shifter cable runs through."

Nope: A) there's only one cable stop, better known as a pinch bolt, on a derailleur; and B) you do not need to do this. In fact, you SHOULD NOT do this! The only times to loosen the pinch bolt is to replace the friggin' cable or when the barrel adjuster can no longer take up the slack – and then, you hold the end of the cable with piers to keep it under tension.

But Gillis pressed on, telling his readers to,

"Pedal your bicycle by hand so that the chain shifts to the smallest gear settings [sic]."

In point of fact, that's exactly how someone who didn't know what he was talking about would say to shift the chain to the smallest cog. "[S]mallest gear settings" is ambiguous at best, and stupid in general. Next, Donovan mumbled some rubbish about limit screws:

"Tighten the high limit screw on your rear derailleur..."

...immediately followed by,

"Adjust the front derailleur low limit screw..."

Ummm, Donovan? were you trying to tell us that adjusting the front derailleur affects the rear derailleur? You do know they're controlled by different cables, right? Sheesh.

Like most eHowians, Gillis probably cribbed his instructions from the mechanic's instruction sheet for installing a derailleur; although he had nothing at all to say about the B-screw. No, the only useful information Donovan gave his readers was this:

"Tighten your tension adjuster located on the back of your derailleur with the shifter cable running through it if your bicycle does not properly shift..."

...and that was essentially a throwaway that used the wrong terminology for the barrel adjuster.

Whatever the case, We sure as heck aren't gonna take Donovan Gillis' word for it. No, we're much more likely to trust the pros at Park Tool, who published useful (and accurate) instructions... unlike our Dumbass of the Day. Oddly enough, the reference Gillis claimed he'd used to write this dreck was... a book published by Park Tool.

DDIY - BICYCLES