Dual Drive earwax

One of the early repairs this year is a Cannondale hybrid with SRAM Dual Drive rear hub. The owner said the bike had been stored for a couple of years. He reported no functional problems, only requested that we figure out how to raise the handlebars.

Dual Drive uses internal hub gears combined with a freehub body to provide a set of external gears shifted with a derailleur. This particular bike had a three speed hub.

A single unit controls both internal and external gears

The control linkage for the internal gears has been disconnected in this picture. 

While I had the wheel out for truing I noticed that only one of the internal gears was engaging. I remounted the wheel to confirm this by reconnecting the shifter. Yep. It was totally air pedaling in low and medium gear ranges. This was not just an adjustment problem. 

With a little Internet mining I got to a tech manual on SRAM's site that showed me how to break into the thing, but I saw nothing in the schematics that suggested an obvious flaw that would lead to this kind of gear loss. The troubleshooting guide made no reference to it. Based on some residue on the end of the hollow axle I suspected congealed grease in the "lifetime lubricated" inner recesses. I flooded the hub with light oil and left it overnight. 

This morning it works.

The all-seeing, all knowing mechanic

This morning on my path commute I came up behind an older man on a hybrid bike. Usually riders and walkers hear me come up behind them. They generally prefer to pull aside. Not this guy. He entered a long stretch where the path runs between the rails. I would not be able to pass him without making a point of inconveniencing him.

I had to laugh, being stuck like a motorist in traffic, or like a driver behind a cyclist where it isn't safe to pass. I had plenty of time to think about it as he made his leisurely way, apparently unaware I was back there at all. I stayed quiet so he wouldn't feel compelled to make room for me in the narrow confines of the rails.

Long minutes passed. I scrutinized the details of his bike. Why was he in that strange gear, on the small chainring up front and the smallest or next smallest cog in back? Were the shifters acting up? I checked his crank to see if it was a crank of death. Tne brakes indicated it was about a 1998 bike, safely past the Crank of Death era.

The tires looked like about 700X35, with no bald spots. I couldn't guess at chain wear, but it looked like it needed lube.

Finally we moved out from between the rails. I gave what I hoped was a cheery greeting as I passed. As soon as I got ahead of his wife I sprinted away. I was late for work.

At the shop I was chatting with my coworker as I unloaded my bike. Up the stairs came the guy from the bike path. He did not have his bike, but I recognized him.

"I want to get a bike tuned," he said. "And I want to know if it will take wider tires."

"Oh yeah, it looks like it probably will," I said.

He looked at me strangely. "How do you know that?" he asked.

"I was behind you on the path," I said. I wish I could have made it more mysterious. At least I had that one moment where he thought I had psychic powers.