Monday, December 14, 2009

Grease Remains a Factor

Despite upper management's wish that the back shop could convert fully to ski mode, the bicycling public continues to seek our aid.

On Friday, an older gentleman who rides his mountain bike relentlessly came in because the freehub ratchet had started catching, causing the rear gears to fix for a moment. This pushes a loop of chain over the top. If the ratchet breaks loose and allows the gear cluster to coast freely, the derailleur spring can take up the slack or the rider can take it up by resuming pedaling. If the rear gears remain fixed, forward motion of the bike pulls more chain until it rips the derailleur apart. This rider's bike was still at the intermittent stage. He noticed only skipping in the gears.

For some reason, we had not needed to replace a freehub body in a long time. We keep a few on hand. With Shimano's bewildering array of variations, we might not have the exact unit, but we can often improvise to get one to work.

In this case we had the exact match. The surgery is messy, but routine. It was trickier than usual this time, because I shared half a narrow bench with the ski waxing operations on the other side. Grease and oil do not go well with ski bases. But nothing went wrong.

While the first bike was still on the stand, another frequent rider came in with her bike. It had the opposite freehub problem: failure to engage. Cold weather makes this problem worse, as dirt or congealed lube keeps ratchet pawls from springing outward so the gears can drive the wheel.

In both cases, the bikes were old enough that I had to do some research in our archive of old Quality catalogs to trace part numbers to our current stock.

I thought I had a matching freehub body for the second bike. I confidently assured the rider I would have it for her the next day. She's a dedicated rider and all-season commuter.

Shimano had other plans for us. This woman's bike had an RM-30 hub. The splined interface with the hub shell differs completely from every other Shimano freehub. I didn't have one and couldn't possibly fake it.

The ratchets had engaged once the bike thawed out. I flooded the freehub body with light lube so that it might work well enough while we wait for replacement parts to arrive. I chilled the bike for half an hour outside before I test rode it. Unfortunately, the temperature had gone up to 34 F, so I don't know how it will fare below freezing. I did not declare it cured, only temporarily in remission while we wait for the new part.

The bench is degreased again. We shall see.

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