Saturday, July 28, 2012

Sacerdos ab ordinario, rite confessus,...

One of our chronic problem customers has been destroying front derailleurs at a rate of about one a month since April. The first one was simply old. It had been on his bike since about 2005. He rides a lot and, judging by the look of the bike, without finesse. But something more persistent seems to plague him.

This bike was supposed to be his fresh start after he beat his old hybrid into the ground. It's a Fuji Roubaix, a moderately decent road bike. He's had to replace wheels. He trashed a carbon fork. He was plagued by flat tires for the longest time. He's had shifting problems. As annoying as the endless series of mishaps and accelerated wear and tear has been, we could generally find cause for effect. Until the Plague of Front Derailleurs, that is.

By the end of yesterday, an hour after closing time, I had looked up the Rite of Exorcism on line. I'd thrown everything else at the bike. I was ready to dump some major Latin on it. Then I saw it was 15 pages. Fun's fun, but that's a lot of "...aut saltem corde peccata sua detestans, peracto, si commode fieri possit, Sanctissimo Missæ sacrificio, divinoque auxilio piis precibus implorato, superpelliceo et stola violacea indutus, et coram se habens obsessum ligatum, si sit periculum, eum, se et astantes communiat signo crucis, et aspergat aqua benedicta, et genibus flexis, aliis respondentibus, dicat Litanias ordinarias usque ad Preces exclusive..." And so on.

At least we finally got to see what he's doing to mangle his derailleurs in his own unique way. The first one had broken at the front of the cage so it could not push the chain effectively. The second one went the same way, but also had the outer plate of the derailleur cage peculiarly bowed outward. The third and fourth derailleur have also had that peculiar outward bend to the outer cage plate.

The rider had neglected to mention, and the bike had failed to show us on any test ride until yesterday, that the chain was hanging up on the outer chainring when downshifting under load (his standard MO, apparently) and getting dragged up into the derailleur. Each incident progressively spreads the cage more and more until the bike will barely shift.

But here's the kicker. We have now changed absolutely every component involved: front derailleur, chain rings, chain, bottom bracket bearings, everything. All brand new. Chain still jams.

ADJÚRO ergo te, omnis immundíssime spíritus, omne phantásma, omnis incúrsio sátanæ,...

I might just resort to the Holy Sledge Hammer and call it good.



7 comments:

Anonymous said...

Having taken Spanish instead of Latin in High School, I thanked the Holy Programmers for Google Translate!

We recently went through a similar predicament with one of our ancient (ca. 25 yrs old!) tape drives at work. One of them kept giving generic error messages whenever it was used, when the others didn't complain at all.

We traded every part, one by one, between the bad drive and a working one, but every piece of the bad drive worked in the good one.

Never did figure out what was wrong, and we did consider the big rubber mallet...

cafiend said...

I lifted the Latin directly from a Catholic website. I also found English versions of the Rite of Exorcism, but the Latin has a wonderful quality of incantation.

cafiend said...

Your story about the tape drive illustrates exactly the same kind of incomprehensible malfunction.

Matthew Boulanger said...

My guess is he's shifting all the way up the cassette before dumping the front ring, too. (starting the shift from a cross-chain position) or maybe the opposite (getting down onto the 12/11 and then dumping the front ring to a cross-chain position.) I'd prescribe a single 39T ring up front and a chain watcher.

But man, front derailleurs are usually the least of my worries. Line 'em up, get the height on the seat tube right, tension on the small ring, set the limit screws, done.

Could he be doing something weird with the trim, too? Like dropping from the big ring is only taking it back to the "trim" position?

My other guess would be the culprit might be a cheap trunk rack with multiple bikes on it with the pedals from bike #2 bashing the derailleur on this bike out of alignment, then hard shifting under load exacerbates it.

cafiend said...

Most of the time he rides from home, early in the morning, so the bike doesn't ride on a rack. He does some organized long rides, but his problems on those so far have been tire-related.

I don't think he has a specific shifting pattern like running the whole cassette before shifting in the front. I am betting that he keeps pressure on the pedals. But the chain isn't getting wedged on the big ring by the force of the initial shift. The derailleur cage pushes the expected section of chain off the ring. But then the last link in front of the shifted segment refuses to release from the tooth it's on and gets dragged up into the derailleur cage with a doubled section of chain following it. The bike continued to do this with every piece changed and with three different chains.

Matthew Boulanger said...

This sounds intriguing. It would be frustrating if I was trying to fix it, though, and even moreso if I was trying to do so professionally!

One more thought- is it possible for the derailleur to be set up in any more of an aft position, or at least to play with he angle a bit? Toe it out a little bit so the first contact with the chain on a downshift happens near the rear part of the cage and on the first aft tooth of the ring to normally have any chain on it?

I look forward to hearing if you find a solution.

cafiend said...

Derailleur angle does affect shifting speed and precision, as well as how easily the chain pops off the high side and drops onto the crank arm. On this bike the front derailleur only becomes reluctant to shift the chain after the cage has been mangled by the jammed links.