New chain, old cassette, chain shift under load
 

As the title says, I recently got a new chain to replace the old one but left the cassette. Whenever I shift under load, or sometimes even on a hard start, the chain will either "crunch" or jump between gears rather than go to the gear that I want. I'm assuming (probably correctly) that it is the cassette, but I was hoping to check with good 'ol BF to see if it's some other problem I'm overlooking instead.

The chain runs fine when kept in the same gear, so it's not a stiff link or anything like that. I did use the old SRAM powerlink, so that may have a different pitch. However, my chain problems don't seem location specific.

How old is the cassette? Is the chain the same speed (or roughly) as the cassette? For example, is the cassette a 10 speed cassette, but the chain is a 8/9 speed? Did it work fine before the chain change? It may be as simple as you may have bumped the derailleur and it needs to be adjusted via the barrel adjuster.

The cassette is about two years old, but ridden only moderately (<50 miles a month?) Chain is 9-speed, and so is the cassette. The old chain was doing this as well, which is what actually prompted me to change the chain. It can't be the derailleur either, as I use friction shifters.

Sounds like the cassette is worned as well. I bet you worn it by running a worned chain. Time to replace it. This is the main reason why shops tend to replace both the chain and the cassette at the same time.

Shifting under load is never going to work well. But a big load, like a "hard start" could flex your frame and cause some issues.

I think the first question to ask is how does the bike shift under normal conditions? If that is ok then your problem is probably not your chain and cassette and you can start looking at things like shifting technique, frame flex and cable friction.

So what's the advantage of paying twice as much for this:
http://www.jensonusa.com/store/produ...ette+2010.aspx

Rather than just getting this:
http://www.jensonusa.com/store/produ...ette+2010.aspx

Bike shifts all right when done perfectly (i.e. lighten load for shift). If I don't lighten the load by much, it'll occasionally skip.

http://www.treefortbikes.com/product...-Cassette.html

Better price

When I mash down on the pedals on my hybrid the chin slips on the cassettes 2 lowest gears. "They're loose!" LBS wrench tells me. I could barely notice it but they were. I screwed them up somehow swapping them out with another set. Spaced out a spacer i guess. You live. You learn.

Less weight. You get less for your money with the more expensive model. In the 11-34 models, the 970 is 42 grams lighter. Possibly some of the material is slightly different to account for that weight difference.