Have been experiencing this new phenomenon lately, and I was wondering if somebody could point me in the right direction to figuring out what is going on.

While going downhill, I will typically "pump" over bumps. (Unweight the bike, and allow it to come "up" over the bump, then I "push down" on the backside to gain momentum). Recently, say over the last 2 weeks or so, I have began to notice that there is a "ker-clunk" going on somewhere in my drivetrain as I come down the backside of the bump.

I, cautiously, was looking down at the drivetrain last night as I was going over some bumps, to see what was going on, and it seems as if the top of my chain (from the top of the cassette, over the chainstay, to the top of the chainring) is becoming slack. It then slaps against the top of the chainstay, and then will become taut again, either as I coast, or as I start to pedal.

The freehub seems to still freewheel quite easily, and I cannot find any binding. Bike seems to ride, shift and do everything else pretty normal.

Any ideas of what could be causing this?

Thanks!
Pop-a-wheelie!

Last night, I checked that the chain was not stretched. I also cleaned and re-lubed it, with no change. My derailleur hanger was a little loose, so I tightened that a bit. Seems like my rear derailleur cage (and jockey wheels) had good spring tension. Thank you!

It is almost without doubt drag starting in your freehub - with a great degree of frig you can sometimes dismantle and lube them - but its time is nearly up.

Freehub.

I agree with the diagnosis, but disagree that it means the hub is nearly done. Some hubs require frequent re-lubrication, such as Mavic. It doesn't necessarily mean they are worn out.

During my ride yesterday, I told my buddy what was up, and he said "You know, my bike is doing the same thing. I think we need to pull the freehub off the wheel, and see if the pawls are all gunked up." So I pulled my wheel apart last night, and I have a broken hub.

That sucks! Looking at the splines alone, I'd guess that hub is not too old.

Good eye, Colin! I bought the wheelset in February. It has an XX cassette on it, which I think is pretty easy on a hub. I shot a picture of it to my buddy, and he had a GREAT idea! He said "We should not ride our bikes so much, so that way they will last a lot longer." Genius!

That's a new one. Stinking Idaho Brutes! Was there some interbreeding with a Sasquatch in your past?

Don't see people breaking hubs.

Not in 5 months, typically no.

Papa, did you ride a lot in the rain or do some river crossings?

I am a fair weather rider! Our weather is ride-able 364 days a year, so I take that one bad one off. Honestly, I try to stay out of the water (and mud); and am not a jumper. I was wondering if I was torqueing the lock-ring on the cassette a bit too much? Other than that, this is a bit of a mystery to me.

So, as my buddy and I were riding today, I think I might have an idea of how this happened. Bear with me here. I have two mountain bikes: hard tail with a 1x10 drivetrain that I typically ride in the lower Boise foothill range. Fast, flowy, non-technical trails, and not anything too steep that that bike cannot climb. As the weather gets hotter, we go higher up, and that is when the fully suspended bike with a 2x10 drivetrain becomes the bike of choice. I typically ride one of them exclusively, until something pushes me onto the other. I fall in love with that bike, and ride it exclusively until something pushes me back onto the first, of which I then fall in love with that bike again, and the cycle repeats. Riding each bike will cause me to change my riding style. Going from the HT to the FS is no big deal. Going from the FS to the HT can cause problems. I get lazy on the FS, stay seated, and plow through anything. When I get on the HT, you simply HAVE to unweight the seat when you are going over rocks, jumps, or other trail debris. About three weeks ago, I had been riding the FS pretty much exclusively, and was pretty used to being able to stay seated and plow through anything. I hopped on the HT, and during a lunch-time ride, we were connecting two mtn bike trails with another trail that the off-road motorcycles have access to. That trail has some whoops on it that are awkwardly spaced, and are about 3 to 3.5 feet from trough to peak. I was carrying about 20-25 mph, and got a little katty-whompas in my timing, and ended up having my sit bones smack into the seat when the bike was going up the face of the next whoop. I have NO IDEA how I did not wreck, but I hit so hard that it snapped the carbon seat post in half. I have no real idea of where blunt forces are transferred through the bike, but I know that I hit that seat HARD. Is there a possibility that the same forces snapped the inner workings of that hub? (Sorry this is a super long paragraph, but for some reason, hitting the "enter" button does not forward the curser to the next line...)

Glad all that was broken was bike parts. Not body parts.

Yeah, anything involving tailbone immediately makes me cringe.

I wonder if that could do it, Papa Wheelie. You would have sent a lot of force into the bike, and therefore the axle and eventually the wheel hub. The part that connects your axle to the hub is the freehub, so it makes sense that it could have been the cause. And it does seem like the part where your freehub broke would be a weak point. Hmm...

And I also don't know how you didn't crash hitting hard enough to break a post. Damn. Glad you didn't go down/get hurt.

Glad to hear your body wasn't injured just your posterior. Seriously, freehubs do gum up and require flushing and relubing occasionally, and when overhauling hubs this is easy,and works wonders for flushing and regreasing freehubs: Free hub Buddy by Morningstar.https://www.morningstartools.com/Pages/FreehubBuddy.aspx
Cheers