Unusual Clunk on Pedal Start
 

Recently picked up a winter bike that is a full Shimano 105 setup, and I have overhauled the whole bike to near perfect condition. I threaded in pedals to take a test ride this morning, and was surprised to hear a strange heavy, hollow thunk coming from the bottom of the bike, on initial pedal force. It doesn't happen every time, but every so often on pedal start. It's not a sound I have ever heard on a bike before.

I pulled the cassette off of the rear hub and cleaned everything and reassembled, and tightened the cassette properly, and the sound still exists. My next step is to disassemble the bottom bracket and see if there is anything unusual there. It's a TruVativ GXP BB, and I know they aren't favorites of many, so it might be something failing there.

When I got the bike, it was visually not maintained, covered top to bottom in mud, grime and a little rust on a few steel parts. I know that there are things that I will uncover as I go, but this one is confounding me. I can't tell exactly where the sound is radiating from, so I'm throwing darts with my eyes closed trying to guess what the sound could be.

Anyone have a similar experience or have any ideas? No other sounds or red flags anywhere except the front of the first pedal stroke.


Guesses?

My guess is the one of the bottom bracket cups needs to be tightened a little bit.

That was my guess. The cassette was the easier of the two fixes... tomorrow morning the BB comes apart to be cleaned and re-assembled. I hope everything is still in working order and it's just a simple torque to fix.

Lose headset?

Subscribing to this thread to see what suggestions others have and what the solution ends up being.

I'm experiencing something similar on one of my bikes. The pedal feel and sound is similar to the clunk when setting a quicklink via the pedal method.

What rear wheel, hub? Mavic by chance?

No, Ritchey Aero Comp hubs, Shimano cassette.

Never experienced but curious to find out root cause.

Ok, so that was... something.

Spent a good part of the morning pulling the cranks (easy) then trying to remove what appeared to be a slightly boogered up GXP bottom bracket. The drive side came off fairly easily and without any issue. Then the fun started.

My Park GXP bottom bracket tool didn't fit the non-drive cup. At all. I tried to clean up the chewed spline lugs with a small jewelers file, and nothing worked. Cleaned up the exterior of the drive cup with a small flat file and it still didn't fit. Finally ran a digital caliper across the diameter and FFS, the non-drive side up was 45.10mm while the drive side cup was 44.10mm in diameter across the flats. Am I losing my mind? Is this a thing? I've built a handful of GXP bottom ends, including my two other bikes, and I have never seen a BB cup size discrepancy from left to tight side.

Then it got good.

I cleaned up the cup all around with a file and Dremel, because at this point all hope is lost and I'm replacing this POS ASAP. I got it to a point where the Park BB socket would uncomfortably be persuaded on. No looking back now. Soak in Kroil, heat up the BB shell, pull out the breaker bar and go to work.

Twisted my 1/2" to 3/8" drive adapter in half. No joke.

Pull out a 3/8" torque wrench, which I wanted to avoid, and give it one more shot to loosen it up before going completely medieval on it. Force, force, force, force, force, SNAP—it came loose. And in the process, my body mass and all of my force came down mouth-first on the top tube. I thought I put my teeth through my lip. Once I started seeing normal colors again and stopped swearing (and feeling for my lower teeth), I got the rest of the drive cup out.

This damn thing is 1mm larger than the other side. This is insane. I think it's TruVativ, so scratch that brand off of any future purchase list.

BB is cleaned and open, and I won't be able to continue troubleshooting on this until the new BB comes in next week. But I got to thinking while I was wrestling with the BB.

What if a single pawl inside the rear hub is seized or broken? That's kinda what it feels like when the klunk happens. Like it's one spot inside the rear hub. The sound seems to be that hollow cassette sound, only deeper, heavier and louder—but only once in a while.

Anyone know if the Ritchey Aero Comp hub is rebuildable?





I need a beer.

Photos for fun...

Hahaha, yeah, no.

I've had this exact thing happen with a pawl that was binding. Cleaned grease out, replaced with chain lube. All good now!

Ooooohhhh, you might be on to something.

Bears v Packers coming up in 20, so I'm taking a break now. Need to give my hands and wrists and lower lip a little time to heal up.

Fun

I'd have put a pipe wrench on it if I knew the BB was toast. If you have not tried one I think the Wheels Manufacturing GXP BB is a really solid value.

As an old GF used to say 'split my lip, bog'd my trip'

PS I hate working on bikes :-)

And yeah, pull that hub apart and take a look see.