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My SRAM 3x7 hub "twitches" (for want of a better description; the end of the indicator chain pulses rhythmically while pedaling). Is this normal, or OK?
When the chain on your SRAM Spectro 3x7 hub pulses in and out, this is an indicator that the hub is between gears and the cable tension needs to be reset.
Reset the indicator chain to cable clip connection. Start with the cable tension loose. Ride around on the bike, shift, and watch the indicator chain. If the chain pulses in and out, tighten the cable tension by one click of the cable clip. Test ride again and continue to tighten up the cable tension one click at a time until the chain no longer pulses.
The most common thing people tend to do is to over-tighten the cable to the 3x7 hub. When properly adjusted, the cable should be somewhat slack.