I have a hard tail with all new drivetrain. Cassette, chain, cable, chainrings, crank, cable housing, and the hanger was checked for alignment. Temporarily I was using a spare derailleur, a lower end Altus. I had some money issues (yay, student loans) and kept the Altus longer than planned. I was having gear slip problems, despite the new drivetrain. This left me confused on what to do, since everything was new and even the LBS said things look good, are set up right, and nothing is worn, etc.
I got my new derailleur in, an LX, and the problems are gone. I've put 70 hard miles on that thing already without a single issue.
Upon visual inspection, the pulleys are not worn at all (they were simply a little dirty, which even after cleaning them didn't help) and the spring tension felt good. The spring tension on my Altus was better than my brother's Shimano Tourney, yet that Tourney won't slip for nothing, yet my Altus does. There is also no damage to the Altus and the cage appears to be very straight. It is set up correctly with H/L limit screws as well as B tension.
This is just a question with trying to understand exactly what *could* be wrong with the Altus. No matter what, a derailleur shouldn't just allow users to torque down on the pedals and it slips. Even lower quality ones.
Keep in mind, this slippage I experienced wasn't every 5 seconds, but it was common enough to drive me crazy. Plus, I was able to re-produce the slipping on flat ground without any rough terrain.
What could have been up with the Altus?