Coaster brake rear hub is spinning "freely" when I pedal forward
 

As the title says, when I pedal forward sometimes the pedals just go forward, without the rear hub catching and moving along the rear wheel the right amount as well. It can be quite surprising.

I thought the locknut was loose, so I removed the wheel and tightened it, put it back on and went for a ride and it still does it.

What is happening? Can it be fixed? Here are some OLD pictures of the hub and internals (It is a hassle to take apart the hub so I don't want to do it until I get an idea what is wrong and how to fix it).


https://i.imgur.com/sEqk4wb.jpg
https://i.imgur.com/eRqstS0.jpg
https://i.imgur.com/7GkZcuK.jpg

Coaster brake hubs depend on a Bendix clutch. The core elements are the helix on the driver (where the sprocket attaches), and the clutch that rides on it.

When you pedal the helix drives the clutch to the right to engage and drive the hub shell, when you coast, the viscous friction and turning shell drive the clutch to the left, and when you back pedal, it presses into and expand the brake shoes.

So there are two common causes of failures like yours. The first is wear and low friction, allowing the clutch to slip rather than bite and positively drive the shell.

The second is sticton at the helix, causing the clutch to turn with the driver rather than stay still and be driven to the right and engaging.

Different hubs use various methods of providing drag on the clutch, so it won't turn with the driver. I can't tell from yours, but it probably relates to those two tabs on the left end of the driver. Or it might simply be wear, or too much sticky grease on the helix.

The only way to fix it is to take it apart. Does not really help to guess what the problem is. In over 20 years as a shop mechanic, plus many years before that owning and working on coaster brake hubs, I never saw one not fixable with an overhaul, and never saw one not driving due to wear.

With this symptom, the first thing I check is the lobes on the cog. I've see them worn down to the point that they no longer engage the notches in the driver and just spin on it.
If that can be ruled out, then it's time to delve deeper.

Autocorrect strikes again?

Yes, I typed that post on the Samsung tablet. I even caught and corrected it once, but missed the second. Apparently helix isn't in the dictionary, so no matter what I try to type, it comes out heli-----copter, and you have to go back and force it to accept what you actually type.

The most common cause is....

The spring inside the clutch must not spin freely. It must have some drag in order to prevent the clutch from spinning with the driver when the driver is trying to pull the clutch to the right side of the shell.

I remember when I was a kid, when my Bendix started to misbehave, my dad would simply disassemble the whole thing, clean the parts, re-assemble with new grease, and it would be good as new. This is something that can be done without true diagnosis, and might just solve the problem. And you can look for obviously worn parts at the same time.

The easiest coaster brake to service.

Get rid of all that old grease, clean and relube. In the absence of any obviously worn or broken parts, a few minutes of "dirty work" and fresh grease will almost always restore a Bendix to full operation.

Hi i am very knew to bikes and the parts im only 12 but very intrested in bikes and I of course know the basics like changing the tire and the inner tube but like the title of the thread my bike is doing the same i took it apart and it was very greasy and i diddnt wipe it off and ive really never had a problem until i tried to put a different rim on my bike it was a hand me down so it was fairly old but i was wondering if u had any tips to getting it working again and if i absolutely need more lubricant like would i just be able to wipe it of and just put it back on bc i dont have any lubricant feel free to email me at juhernan@gilbertschools.net