Popping/pinging noise on largest rear cog
This is going to be difficult to describe without seeing it first hand, but I'll try.
Recently replaced my 9 speed 12-25 cassette (old HG70, new HG50 aka Tiagra), 42t ring, and chain (old shimano HG73, new SRAM PC-951), just made a small barrel adjustment and was good to go. Test ride was great, drivetrain shifted fine through the whole range and was quiet aside from my derailleur cage rubbing my chain on cross gear settings, but I don't think that's related.
Here's my problem: under torque, specifically standing climbs and/or forceful starts from a stopped position, I get a metallic pinging noise in middle front (42) - large rear (25) combo. I also feel a slight popping in the chain when pedaling. As soon as I shift one cog over (23) the noises disappear. There doesn't appear to be any skipping/slipping as best I can tell. Again, this is only under high torque - this gear combo on flats or in the workstand run fine.
Last night I put the old cassette back on, tried to climb on the 25, and the noise was gone. New cassette, noise is back. I tried loosening/tightening the lockring and backed the RD low stop away from the spokes to no avail - while initially I was afraid the noise might be the chain hitting spokes, I'm leery since swapping cassettes makes it disappear. Visually, my RD cage appeared to be in the same position relative to spokes with either cassette on the 25 cog. I can't imagine there's a width difference between the HG70 and HG50, so RD position shouldn't have to be changed.
I know this is vague without experiencing it first hand, but any ideas? I can't replicate the problem in a workstand, it has to be under torque.
Last edited by atrocious; 11-19-09 at 04:08 PM.