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My son's bike has a SRAM i3 internal gear + coaster brake hub. It has recently started sometimes only activating the coaster brake after backpedalling a good one or two full revolutions. When in this situation, it sounds somewhat clunky or grindy when the brake finally activates. However, sometimes, it kicks in straight away. I haven't found a solid pattern to when it works and doesn't, but it seems that the brake is more reliable in gear 1 than in gear 3, though I might be wrong about this. Can this adjusted/fixed, or do I need to replace the mechanism?

EDIT: After experimenting with the brakes and gearing with the bike in a stand (previously I had been trying while riding it) it seems that in gear 1, the brake always works fine. In gear 3, it requires almost a full rotation backwards before the gear engages. While in gear 2, it's somewhere between - about half a rotation.

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    Is the "arm" from the hub tightly attached to both hub and frame? – Daniel R Hicks May 19 at 0:42
  • the brake arm is tightly attached to the chainstay. As for the hub, I can't tell as I haven't got a thin spanner as large as the nut that's there, but there is a locknut, and it seems tight, but I can't be certain. However, I would be surprised if it had come loose on its own as I haven't touched it, and it's been running fine for ages. – askvictor May 19 at 1:44
  • How much mileage has this gearbox done in its life. How long/far since the last oil change ? – Criggie♦ May 19 at 4:37
  • I bought it second hand, so don't know the previous history, but it's a kid's bike, so it won't be massive mileage. Since we've had it, it's done less that 1000km. Never had an oil change/service since I've had it, so I suppose that's what I'll look at doing. – askvictor May 23 at 0:17

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