mrandradej

So back in August my sister gave me her old Trek 820 AL (https://www.bikepedia.com/quickbike/B...k&model=820+AL). It wasn't well maintained and not used for years. It has served me well though being able to do all my local errands and commuting to my part time job on the weekends.

It has begun to wear down though. I have had this problem that sometimes when riding, I tend to hear a snap on the cranks (something else?) and the cranks start moving loosely/freely without any tension making it impossible to continue pedaling. Could it be a problem with the BB or the cranks/something else?

So I decided to change the cassette and chain first. I cleaned out the old grease on the bottom bracket shell and put new grease on. However, after installing the new cassette/chain and cleaning out other areas the problem remains. I will post pictures of the parts as well as a couple videos showing the issue.


Old cassette and crankset


old crankset


current bottom bracket


new cassette installed


old chain vs new chain



If it is a problem with the crankset/BB I was thinking of going with this combination:
https://smile.amazon.com/dp/B002I7K5L...I3NF8RTDAZMMC1 (170 x 22/32/42)
https://smile.amazon.com/dp/B00629OC9...I2UCUSQTWBYJQN (73 x 122mm)

But I will await opinions from the experts because it might just be a simple fix. Thanks!

cny-bikeman

Need to use some logic here. If the chainwheel is moving the chain, and the chain is rotating the cassette, but the chain is not driving the rear wheel, then the problem cannot be the cranks or bottom bracket or cassette teeth. The problem is your freewheel or freehub body. Changing the cassette (the part you show) will have no effect. Flushing out the freewheel/freehub may work, or you may need a new one.

CustomSteel

I would have to agree with cny-bikeman on the freewheel/freehub body (looks like yours is an old freehub design?). I had this happen with an old high-mileage King Kong freehub body. The pawls inside of it were all stuck closed, so the cassette would suddenly start spinning freely. It would also flop around a bit because there was no tension inside of the freehub body. I too the freehub body off and spent some time flushing WD-40 through it and spinning it until the shaft stopped flopping around inside of the shell. It also started locking properly as well. After it tightened back up and was functioning properly I flushed out the WD-40 with some good oil. I don't care much for that particular freehub body (it's a rip-off of the Shimano design that came out at the time), but I haven't had a problem with it since.

Just FYI, my freehub body was attached to the hub with thread locker. I'm not sure if this was/is common, just something to be aware of.

mrandradej

Thank you both.

I will take the time this weekend to disassemble the freehub. Gives me a chance to learn a new function of the bike

Angry_Monkey

I don't know where you normally keep the bike. If water has worked into the free wheel/hub it may have frozen the pawls into the closed position allowing everything to spin like that. If you don't already, take it inside and allow it to warm up and dry out. WD-40 and/or compressed air will chase water out. And then lube. Try this before opening everything up.

~Monkey~

CustomSteel

Just a note for clarification, I didn't take my freehub body apart. What Monkey described is the same process I mentioned earlier. It took two evenings for everything to start working properly, which came to somewhere between 3-5 hours of working with it off and on. I had to let the freehub body just sit with WD-40 soaking into it the first few times, which accounted for a good portion of the time.