At the end of September last year, the m5100 rear derailleur on my Carl Strong frame started making funny noises, and shifting performance deteriorated. I finally narrowed it down to the pulley wheels, and after taking the upper one apart saw immediately that the bushing had failed.
A pair of replacement pulley wheels were only $10, but would take a few days. I saw that there was an ebay offer where I could get a GRX 822 rear derailleur for $80, and decided I'd order that as well and install the first one that arrived.
The GRX rear derailleur would handle a 10-51 rear cassette but was designed for 12 speed. Of course, years of shifting with friction shifters have made me blase about using unmatched rear derailleurs. I figured since the job of the derailleur was just to move the chain from one sprocket to another, as long as it could handle the chain and the cassette's spread I should be good to go. It didn't hurt that the derailleur was a good 40g lighter than the m5100 derailleur that it replaced.
At first, I was actually quite pleased with the rear derailleur. It was a lighter action --- whether it was because the higher end derailleur had smoother bearings or pivots and just a lighter action spring, the shifts definitely felt smoother or faster.
The problem was that the shifts were not reliable. For instance, the 45t sprocket was easily one of my favorite sprocket on the m5100. However, it was no longer quiet, making a strange sort of noise whenever it was on that cassette. In fact, the rear derailleur was finicky about staying on that sprocket. Any sort of nudge on the shifter would knock it off that sprocket. Even stranger, once in a while the chain would slip off a sprocket and then rather than recovering to that sprocket the derailleur would shift all the way down the cassette.
I lived with this for awhile, thinking that it was just a matter of retraining my friction shifting muscle memory so that the shifts would be good. But 3 months later it still wasn't good and worse, the chain started falling off the chainring even when the clutch was on. I went so far as to check the chains for both pin wear and lateral wear, and nope. That wasn't my problem.
I finally pulled off the derailleur and put the m5100 back in with the new pulley wheels, and immediately the problems all went away. So somehow, Shimano managed to make their 12s rear derailleur incompatible with the 11s rear cassette even when you're using friction shifters. That's a level of incompatibility I'd never seen before. One possibility is that you really need 12s chains, but since those are expensive I guess I won't make that experiment. In the mean time I guess I have a relatively new GRX 822 rear derailleur for sale.





.jpg)



