Deontologist

My old chain was both stiff and clunked a lot on my old cassette.

The new chain I installed isn't stiff. I can actually pedal backwards without the chain gaining tons of slack and touching the seat stays.

But the clunking is still there. Anytime I push the pedals forcefully there's a nice clunk or two to greet me. No heavy load, no clunk. Heavy load - you can bet there's gonna be clunking.

I'm suspecting that this is just cassette wear and that I should swap out the old cassette, right? The old chain did have a fair bit of stretch in it. The LBS thought it might have been an indexing issue but after adjusting the indexing to nearly perfect, there was still no difference. Clunk, clunk, clunk my bike goes each time I apply heavy load.

So the issue is probably the cassette right? The last time I had a clunking issue with any bike the freewheel was absolutely spent. In that case there was also the issue of the chain slipping around. In this case my chain isn't slipping anywhere but there's still clunking. So what do you think?

FBinNY 

If the old chain wore the cassette to the point where it skipped, you can be almost sure the new chain will also.

Classic new chain/old sprocket skip is as follows. When you pedal fairly hard, especially on smaller sprockets, the chain will skip 1-2 links with a low clunk and the pedals dropping about 2-3 inches then catching again.

If that describes what's happening to you, then replace the cassette. (hang on to the old one just in case).

Deontologist

Yes. Almost perfectly. The chain ain't slipping side to side to other cogs. It's a big clunk and I think it's almost definitely a forward slip. The pedals do drop a few inches and I'm gonna stay off my bike now because on the way home in traffic it was damn near impossible to start from stops because the chain kept clunking/skipping a few links!

Ordered a brand new Veloce cassette from eBay. Can't wait for it to arrive! Until then my bike's gonna be at home resting!

I'm just really, really weirded out that that cassette and chain wore out so quickly. I've only had the bike for 6 months. Before that it was in some guy's garage for 10 years and he only rode it 20 miles. I believe him because when I first saw the bike it was impeccable; it looked like it just came off the showroom floor. Not a hint of dirt or misplaced grease. In those 6 months I only really started riding the bike in the last 3 months. The longest ride I've taken it on was 70 miles. There is no way the bike has seen more than 1000 miles. I'd be willing to bet less than 500 miles. And here I am with a worn out chain and cassette. What gives?

FBinNY 

I can't say why it wore out so fast, or even if it did. It's always possible that the chain had a few thousand miles on it before you came along.

In any case the best predictor of cassette wear is the stretch of the prior chain. Did you measure it?

In any case, over the net diagnostics aren't super reliable, so save the old cassette in case the new one skips, in which case you'll be looking for another cause.