Bicycle Mechanics - bottom bracket drag/whir

I'm having an issue with my BB and I can't diagnose the problem.

When I backpedal at a decent speed (say 15 mph) there is a whir and a bit of a drag that occurs. Yes, yes...just stop backpedaling. I know, that is the easy fix. But, I'd like to actually solve the problem. The whir seems to occur mainly on the drive-side.

Here is the thing - I had this same whir and it was time for some upgrades, so replaced my BB, chain, and cassettes. Replaced them all with quality stuff - Shimano UN-54 BB, SRAM chain, SRAM cassettes.

Anyone have an ideas?

My chainrings are fine. My deraillers are fine. The only thing I can think of is my derailler pulleys.

Again, I know my bicycle isn't going to explode next ride, but I take pride in taking care of it since it treats me well. It is a ten year old road bike with Shimano 105 components. Chain and things are lubed as well.

"whir"

I guess the first place to start would be to take the chain off and turn the crank forward and backward. This would allow me to narrow it down to front end/rear problem.

Sounds like a bad freehub. Here's why:

The noise is created by an increase in speed and backpedaling. Of your Crank, BB, Chain, Cassette or Derailuer; none becomes more active with an increase in speed but they all are more active during backpedaling (compared to coasting). The wheels inversely, are; more active with higher speed but unaffected by backpedaling...except for one part. The freehub is the only part of the bicylce that is affected by both speed and backpedaling.

Freehubs often have slight eccentricites between inner and outer races, which is usually combined with dust caps or seals that have too much friction. A more expensive freehub will have stricter tolerances and less of these issues. Also, if the ratcheting noise sounds extra bright it needs lubrication and/or cleaning. Dull sounding means lube is too thick or dried up.

I'm going to guess that your chain has some extra slack when the bike is rolling. Am I right?

Hey CBolt, thanks for the diagnosis. I'll have to check out my freehub and see if that is it. Ha ha ha...every time I think I can say I've worked on all the parts on my bicycle...a new issue pops up. Have yet to do freehub work.

As for the chain, I think it is set at a pretty good length/tension. It certainly has some slack, but doesn't droop down.