CVB

I recently acquired a used bike with a coaster brake that buzzes when the wheel is coasting. The brake engages with the expected amount of backpedaling and stops fine, and the clutch engages on forward pedaling just fine, but when the pedals are still, the clutch tends to rub the shell of the hub and make a buzzing noise. There is a very fine interval where you can adjust the pedal position and the noise will disappear, but the default is for the coaster brake to buzz when coasting. The bike itself is only a few years old and looks very lightly ridden (original tires still have lots of tread, paint is fresh, etc)

Things I've tried:
1. Looked at every single coaster brake thread on these forums going back 8 years
2. Read through the following very instructive webpages:
sheldonbrown.com/coaster-brakes.html
https://www.arnettmotorbikes.com/inde...s/Page645.html,
https://www.troubleshooters.com/bicyc...d_overhaul.htm
https://www.parktool.com/blog/repair-...edal-brake-hub
3. I've disassembled the hub, greased everything well (though it was already well-packed with fresh-looking grease), inspected every part for wear or damage, and reassembled it
4. Reassembled the hub without the brake shoes to determine whether it was the shoes or the clutch (it still buzzes without the shoes)
5. Reassembled the hub without the clutch spring to see if the clutch spring was somehow causing the clutch to engage prematurely (it still buzzes without the spring)

I'm totally stumped by this thing. I've ordered new guts for the hub (clutch, spring, and shoes), but I honestly don't see how they'll help.

Any suggestions?

CVB

Any ideas? Could it be a manufacturing defect? Mismatched hub parts?

kingsting

Some of these buzz like crazy and there isn't much you can do, especially the cheap Chinese ones like Hi-Stop.
What happens with these is that the inside of the hub shell gets some grooves imprinted in it from the expander. Probably during the assembly or testing process. You can sand the inside of the hub shell with emery cloth and repack with a thicker grease which will quiet it down some. The noise should go away after a while with use.

CVB

kingsting,
Thanks! Your explanation makes sense. This is supposed to be a gift for my daughter, so I'm going to sand it as you suggest, repack, and ride the snot out of this little girl's bike between now and Christmas morning!

kingsting

Some kids think the sound is cool. If the bike has knobby tires on it, the hum that they make on the pavement will muffle the buzzing somewhat too.

DX-MAN

Hope that works for you; IME, kids don't like it that much -- for coaster-brake bikes, this is return reason #1 with a bullet, where I work.

I was going to suggest a bit looser on the drive cones, it works for many of the noisy ones out of the box here, but you're already past that.

kingsting

We don't get many kids back because the kids don't like the noise. We get them back because the parents think something is wrong. We do get cruisers back when they make noise. Those 26" alloy wheels really amplify the sound!