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The bike I am riding is an older mountain bike that is a cheaper model, likely from Walmart or somewhere similar. I picked it up at the flea market and have been doing repairs on it as a way to learn more about how bicycles work.

I was in the middle of a ride when all of a sudden I lost the ability to use the pedals to ride the bike. The pedals still turn, but they do not seem to be able to turn the wheel. There is some resistance to pedaling, but I think something might have happened in the bottom bracket or in the connection between the pedal arm and the bracket. I took the bike home and flipped it over and am able to pedal it fine. I think the issue only comes up when weight is being put on the back wheel.

Any insights on how to get the bike working normally would be greatly appreciated!

Here are two videos showing the problem:

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    I have edited in the two video links from the comments. They are crucial for making the correct conclusion. Sep 6 '20 at 7:36
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Judging from your videos, it appears that the chainrings and crank are no longer connected. It appears that you have something called a one-piece crankset. If you are confident that you can learn how to disassemble it, I’d say you’re up for the repair.

Once you have the crank off the bike, you’ll be able to see how the chainrings and crank arm are connected. Assess the interface. Is there a threaded ring that may have come loose? Be aware that the hole mounting the chainrings to the crank arm is a D shape, and the fact that it’s able to spin like that may mean that the D shape has been destroyed and turned into a full circle. In that case, the crankset is likely not repairable. A welder could fix it though.

Let me know if you get the cranks off the bike, and then we can go from there. As an aside, your cable routing seems iffy: are there no braze ons to tie the cables to? I don’t believe a bike manufacturer would just zip tie the cables around the frame like that. It’s not an issue other than cosmetics though. It almost feels like the brakes are mismatched too. Why is the cable looping around itself like that?

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    @DanK Ah, I've found them now. And I've edited them into the question. I think, this answer should be the accepted one, even though Weiwen Ng's answer is useful as well. Sep 6 '20 at 7:38
  • I notice that Murray Redwing images on Google do seem to have zip-tied cables on, so normal to this bike. But unusual. One downside to long cable runs like that is any water (condensation) pooling at the low point of the outer will accelerate corrosion of the inner cable. IMHO
    – Swifty
    Sep 6 '20 at 8:15
  • I'll look into how to disassemble the crankset. Thanks for the insights on the problem!
    – Alan
    Sep 6 '20 at 15:07
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    Here is the Park Video on crank removal: youtube.com/watch?v=dpl_wlTBC8k
    – Ron Jensen
    Sep 6 '20 at 15:09
  • @Swifty The rear brake doesn’t look right though. The housing is entering the brake at a very sharp angle.
    – MaplePanda
    Sep 6 '20 at 18:46
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While we don't have your bike in hand, or at least a video of the issue, it sounds more like your freewheel or your freehub has failed. I suspect that new cyclists might say the gears have failed. Edit: This answer actually mis-diagnosed the problem (albeit I'd argue for good reason - it was given before videos were provided!). I'm leaving it up for general information. @MaplePanda's answer is correct.

Inside the rear hub or freewheel, there is a system of pawls and ratchets. These enable you to coast, and they produce a ticking sound as you do. When you pedal forward, the pawls stick in the ratchets. This site has a diagram of a general pawl and ratchet system, reproduced below:

enter image description here

What likely happened is that the pawls aren't engaging the ratchets when you pedal forward. What to do about that depends on what equipment you have. Sheldon Brown's site shows the difference between a freewheel and a cassette hub:

enter image description here

If you have a freewheel that's threaded onto the hub, I'd just get a new one.

If you have a cassette hub and you were determined to do this yourself, you could remove the freehub body from the hub, and see what has happened to the pawls. It's possible that cleaning the pawls and adding fresh grease would restore them to working condition. How to do this depends on the hub construction, but at minimum you have to remove any endcaps from both sides of the rear wheel. These basically thread on to the ends of the axle and prevent the hub from coming apart laterally. When re-assembling, you would have to take care not to tighten the assembly too tight (i.e. to excessively pre-load the hub, which would basically squash the bearings in too tight and cause them to wear out).

Be aware that if you are unable to DIY this, a bike store might help you, but you might find that it's just as economical to get a new rear wheel. It depends on how much labor they need to do to get at the problem. Some cities may have bicycle cooperatives that are set up to let lay cyclists work on their bicycles, and you might want to take advantage of one if you can get to one.

If your bottom bracket (BB) was the issue, you should have a hard time turning the cranks in the first place or you would feel something crunchy as you turned the cranks, but you would still be able to freewheel (i.e. coast without pedaling) fine, and the chain would still transmit power to the cogs (i.e. the geared things in back; new cyclists might call the entire assembly the gears).

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  • Thanks for the detailed response! While the bike is flipped, the cranks work fine and the bike operates normally. When seated, the cranks move, but the rest of the drive system doesn't. If I push the bike the pedals and chain move normally. With enough pressure, it seems that the cranks just spin around the bracket, but the bracket doesn't move.
    – Alan
    Sep 5 '20 at 14:27
  • Here's a quick video I took which shows the problem. streamable.com/k1ldza
    – Alan
    Sep 5 '20 at 14:39
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    Here's a side view video that should make things more clear: streamable.com/hkhp93
    – Alan
    Sep 5 '20 at 15:56
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    This answer was the best guess so still +1 from me, but your new video instead shows the crank arm has disconnected from the chainrings. Please put these video links in your original question. Sep 5 '20 at 22:05
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    The reason if works fine when you're not on it is simply friction. Sep 5 '20 at 22:06

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