Hi all,
I recently found an old derby bicycle in a garage. The Bendix 20 hub does not seem to work properly. The sprocket spins without turning the hub. I took the hub apart but cannot seen to locate the issue. Can someone advise on this, or explain how this hub is suppose to work. Thanks, Andrew

I'm not familiar with the specific model 20 hub, but the basics of all Bendix hubs are the same. They work on the principle of a spiral clutch on the driver (attached to the sprocket). When you pedal forward the spiral draws the clutch to the right where it engages the hub shell. When you coast and the hub is spinning faster than the sprocket, the clutch goes down the spiral and disengages. When you back pedal the clutch moves to the left to engage the brake side of the hub and apply the brake (the actual brake side varies from hub to hub).

Usually there's a spring on one side or the other to start the process.

There are lots of free tutorials on rebuilding coaster brakes, so I suggest reviewing a few until the light goes on and figure out what you're missing (either part or understanding)

Also, check that the 3 drive tabs on the cog are not sheared or worn off, and the cog spins without turning the driver. Best way to check that is to remove the snap ring holding the cog on, and lift the cog off. I have seen this happen more than once, although that was on bikes (trikes actually) in heavy duty usage. Still worth checking before you get too deep into it.

This is a good point, and worth checking if you haven't taken it apart yet. You can check it without popping the snap ring, by simply turning the sprocket while looking at the center of the driver. If the driver doesn't turn, then it's simply a matter of a new sprocket. As Dan said, this is bery rare, but why not check first. Once you have it apart, it's harder to check this without popping the snap ring since it's hard to apply enough torque.

Most common cause for this symptom is old grease hardened up and not allowing the clutch cone to engage. disassemble, clean in solvent and reassemble with new grease. Barring the forementioned tabs on the cog being worn off, and rarely the clutch one being worn out, 9 times out of 10 this will fix your problem.

+10... Bikeman beat me to it. Back when I was working on Bendix hubs (30 years ago now), old, dried up grease was the only real problem they ever had.

Hi all, thanks for the quick responses. The 3 drive tabs on the cog are not worn down. The cog & sprocket are engaged tightly. When the sprocket is rotated via the bike chain, the entire inners of the hub (spiral clutch, shaft, brakes,) all spin as one unit. Nothing seems to catch the hub from the inside to make it spin. The grease inside is original to the bike and extremely viscous. Almost like spackle. I will clean it with solvent and re grease. I'll also try to find some videos on Youtube, and will post my results in a couple days.

Thanks again,
Andrew

That's your problem. The clutch cone and the driver need to slide against each other, not stick. A good cleaning and light grease should be all you need.

Below: driver is part #13, clutch cone is #10

I disassembled the hub and soaked all the parts in acetone. I cleaned everything thoroughly, then greased and re-assembled. Works like new. Thank you to everyone who helped.