Experts, drivetrain question.
I've documented my woes with my XT 12 speed drivetrain on here: this spring a branch nailed the derailleur and pushed it in the spokes, bending a whole bunch of stuff, primarily the hanger and the cage. I straightened everything back but the shifting never got back to perfect no matter how much effort I put into it. More recently I mashed the derailleur into a boulder which snapped the hanger. New hanger went on (I checked that it was straight) but shifting remained sub-par. I continued nailing rocks with the derailleur (alpine riding in the Wasatch isn't kind on gear) and it's now looking fairly haggard with gouges all over the cage and the body.
The main issue lately has been serious hesitation when shifting from 3rd to 2nd biggest sprocket, and to a lesser extent from 2nd sprocket to granny. Shifting is fine further down the cassette (both up and down shifts) but getting up to pre-granny often takes 4 of 5 pedal revolutions and some serious grinding about, sometimes forcing me to double shift to granny and back down (work well) or push the shifter halfway. The B gap is fine, the cable tension is fine, the hanger is straight, the chain isn't anywhere near worn (replaced at 600 miles due to a missing roller), I figured the accumulated wear and bends on the derailleur was the cause and decided to swap it out yesterday. Putting it side by side with the brand new one though it's hard to find any visible bends and other than the cosmetic beating it seems to work just as well as a new one. The cassette is beat though, much more than what I'd expect after about 1000 miles. The teeth that are meant to move the chain up on the 2 alu cogs are chewed to shit and with the bike in the stand I could see that they were basically too worn to properly lift the chain onto the bigger cogs. The next tooth (1st to engage the chain on the new sprocket) is also worn on the leading edge and the chain slips off and falls back down. The steel cogs are barely worn and the difference in shape is impressive:
So, question: can a slightly bent derailleur explain what I would call very premature wear? Something that isn't obvious to the eye but clearly affects the angle at which the chain contacts the teeth and wears them at an angle? If that's the case I'm throwing a new cassette and derailleur on there and calling it good.
The other options is that these XT cassettes are made of solid butter and 1000 miles is what I should expect out of them. If that's the case I'm going to pay the weight penalty and get a full steel Deore cassette and keep my beat up derailleur...
Bookmarks