[volyblmn]

Sorry for the long story, hard to describe what happened. Weird issue riding yesterday, hoping some mystical gurus here can provide input. About 15 min into my ride during a hard pedal uphill, my chain (without any shifter input) did the old 'kerchunk' and went into a different gear. When I got to the top of the hill I shifted a few times in either direction and it felt fine, so I kept pedaling. During a downhill, however, I noticed quite a bit of chain noise/slap which was odd because the derailleur has a clutch and there weren't that many bumps. I slowed down and pedaled around for a bit on a flat area to see what was going on. No obvious issues, got off the bike and checked alignment, seemed fine. Tried to move the derailleur around with my hand and it was snug, clutch worked fine too. When I pedaled backwards, however, I noticed the chain got really slack and flopped all over (normally it just moves in reverse and the amount of slack doesn't change). I started riding again and there didn't seem to be any issues going straight on flat and level. Going downhill again, more chain slap, so I got off the bike and checked things again. Still didn't see anything obvious, so I shifted through the gears in both directions and tried riding again. No issues for the rest of the ride going up or down. Chalk it up to a momentary glitch? Or is it a possible sign of an impending failure? Thanks in advance.

 

[Redlands R&C]

What kind of rear wheel?

 

[volyblmn]

What kind of rear wheel?

Bontrager Duster. Whatever's stock on a Trek Fuel EX 7 29er (2014 model).

 

[iliveonnitro]

If you pedal backwards and the chain gets slack on top, either your cassette or, more likely, one of the wheels on your derailleur is binding. When was the last time you cleaned the gunk that builds up on the derailleur? Are any of the bearings failing?

 

[PuddleDuck]

From what you say about chainslap...

It could also be a worn chainring. I've had similar issues with both mtn and road chainrings that had reached their service life.

Adding to what nitro said above, you should check your freehub:
[1] the bearings could be worn out (which would be evident from their being a lot of play between the cassette vs the hub)...OR
[2] the pawls could be really sticky maybe combined with [3] the bearings aren't spinning as well as they used to (I have a old bike that does this...it's scheduled for an overhaul)

 

[Harold]

2014 bike? just service the whole hub. it's either the bearings or a gummy freehub mechanism, either of which you'll catch if you disassemble it for cleaning and service. you should clean/lube your freehub more often than once every 5yrs in the future, though.

 

[202cycle]

First thing to check is that there is no debris between the cassette and spokes. I've seen small twigs get in there and cause exactly the issue you describe. Always start with the easiest solution and work your way out from there.

 

[volyblmn]

Thanks everyone. No debris in spokes/cassette. Derailleur doesn't have any gunk, but couldn't tell you about the bearings in the jockey wheels. My guess is what Harold said - issue with freehub not being serviced within the last 5 years. Time to hit up YouTube for a how-to, I guess.

 

[127.0.0.1]

the chain may be too short and not causing an issue usually, until you were climbing and settled the suspension just so and in the pizza cog...maxing chain length and possibly bending der cage...so...I'd check der hanger alignment and the der itself, as well as check chain length in the biggest cog...

because this same thing happened to me. was riding fine for a long time until I hit the climbiest of climbs and had to use the 46, and also some uphill chunk...and then shifting became spotty and unreliable. turns out I was 2 links short and bent the rear der.

new chain 2 links longer and new der, zero issues in any conditions

 

[LarryFahn]

The problem is your freehub. That's it.

Ttyl, Fahn

 

[202cycle]

Many of the OEM wheels did not have servicable freehubs. In your case, the freehub would need to be replaced. Trek part #W211339.

 

[volyblmn]

Many of the OEM wheels did not have servicable freehubs. In your case, the freehub would need to be replaced. Trek part #W211339.

Thanks, but that part # shows a 9-speed freehub whereas my bike is 10-speed. Do I need an adapter or something?

 

[202cycle]

Thanks, but that part # shows a 9-speed freehub whereas my bike is 10-speed. Do I need an adapter or something?

Nope, same freehub for 9 or 10. Make sure you get the 11mm socket adaptor with it.