Wednesday, May 20, 2015

Move the finish line

 As you may recall, Jake the Satanic Serpent absolutely refused to shift into the lowest gear on the rear cassette. Based on the noises from the inaccessible interior and the way it acted like it had too much and too little cable tension at the same time, I wondered if the cables had been run correctly when the bike was built. If they had somehow gotten tangled with each other, running a guide sleeve to install new cables would simply replicate the error.

With a bit of time to think about it I realized I could feel for any interference by shifting to the mid range on the rear and feeling the exposed section of cable below the chain stay as I shifted the front. There was nary a twitch.

Jake seemed strangely well-behaved today, even before I started adjusting things. The rear derailleur shifted pretty smoothly through ten of eleven cogs. But that last step, onto the lowest gear, was like a wall.

The limit screws on the rear derailleur were backed out far enough that it would start to shift into the spokes if I pulled cable tension by hand or simply shoved the derailleur over. The problem lay in the ratchet of the brifter itself. It could not pull any more cable. The rear derailleur cable was led properly, but the eleventh cog calls for tension at an angle that reduces the cable pull by just enough to prevent the shift.

If the derailleur won't go to low gear, low gear must come to the derailleur. A 1mm spacer was too thick for the lock ring threads to engage, but I had a .7mm spacer left over from someone else's weird problem. It was just enough to get the shifting to work across all rear gears from both front rings, in today's barometric pressure, relative humidity, wind speed and direction, with brand new cables and housing and everything clean.

That's as good as it gets with a lot of this ultra-modern stuff.

Jake's unfortunate owner is taking up these problems with the shop where he got the bike. I fully expect them to tell him I'm full of shit and the bike is fine.

If it comes back again, choking on silt, I'm going to drill bigger cable exit holes in the down tube by the BB. Maybe I'll cut a few big inspection ports in it, too.

Barcons, man. Eight speeds. Maybe nine. If he really wants to be competitive in 'cross, finicky brifters are just the beginning. He's going to have to turn into one of these neurotics with four different sets of sewup wheels. If that's not where he wants to go, why put up with this shit? Ah, but I ask myself that question many times a day in bike season. People believe the industry's marketing bullshit. They only have a choice of pseudo-racer tweakitude or some other very specific category. Even the all-around roadish bike has to be "a gravel bike" so it can be another freaking category.

High-dollar tickets often start with the words, "my friend gave me this bike." Or it might be, "my friend sold me his old bike when he got a new one," but there's always a friend. Friendship can apparently survive a lot.

The next bike after the Serpent was a Giant full suspension mountain bike, archaeologically dated to about 2004. The guy who brought it in initially just wanted to buy toe clips, a bottle cage and bar ends and install them himself. Cool, no problem. But as I looked over the bike to answer his questions I saw a few things and he began to open up about problems he had experienced with it. It wasn't shifting right. The old Avid BBDB cable disk brakes needed pads in the rear. The right crank arm was floppy loose.

Between the floppy crank arm on the drive side and the fact that the bottom bracket was crawling out of the frame, it's no wonder the bike did not shift right.

Luck was with this guy. The ISIS splined crank arm was not damaged from being ridden loose. I was able to examine the BB cartridge and crank it back in, before graunching down on the crank arm bolts with all the power of a mighty breaker bar.

Note: splined crank arms require frequent reapplications of high torque. They do not stay tight the way contemptible old stone-age square taper axles and crank arms do. Not to say you don't need to check those at somewhat regular intervals, especially after removal and reinstallation, but the square taper interface is supposed to be a press fit. Splined axles are not a press fit. So the bolt has to be tight tight tight.

Notice that the industry has basically abandoned the splined cartridge in favor of the cranks with the BB axle swaged into one side or the other of the crankset itself. This has led to its own set of problems, of course.

Once I had the Giant's BB back in the frame and the crank arms firmly attached I could start adjusting the gears. On the front derailleur I found another moving finish line: Someone had steadily shifted the limit screws on the front derailleur to chase the crank as it moved further and further out. Yep. Don't fix the underlying problem. Just move the derailleur.

Chaos is upon us. You can't look at the whole pile, only at what is right in front of you. Straighten one out, move it along. Grab the next one.

1 comment:

Steve A said...

Perfection avoids both old AND new bikes. It is only the problems that change...