I have a Specialized Epic mountain bike that is about 4 years old. I ride in a weekly race series and we race rain or shine. After 3 weeks in a row in the rain and heavy mud I found it very difficult to shift gears so I took it into the shop and had them replace the cables and housing for my gears. I could then shift again but the chain would continuously skip out of the sprocket at the rear for no reason and jump to another ring. It was even worse when I pushed hard like up a hill. I took it back and they got it so it was smooth on the stand. Within 1 min of me riding, same problem. The shop now has replaced the cables, the rear derailler, the chain, the rear cassette and the shifters and it is still doing it (although not as bad). The bike shop guys test rode it and they said it was fine. Two different guys rode it (both are serious racers) but they weigh about 130 and 150 pounds and I am 190 and as soon as I ride hard it still happens. I trust them as I know them personally and have done a lot of business with them over the years so I do not believe that they are trying to screw me. I am really frustrated. Does anyone have any ideas why this would continue to happen even when everything is now new. Thanks.
replace the cables and housing for my gears. I could then shift again but the chain would continuously skip out of the sprocket at the rear for no reason and jump to another ring. It was even worse when I pushed hard like up a hill. Thanks.
Wow, same thing happened to my friend's Specialized. I did him a (free) favor and replaced the cables and housing, and when he exerted any effort, the rear der would shift and pop. We replaced the cassette and chain, but results were the same. The bike acted fine in the stand - shifting very smooth and responsive. Well, after much gnashing of teeth, it turned out I cut the cable housing a bit too short. As the suspension flexed (like when powering), it would stretch the cable a bit, and cause it to shift. Basically my bad. You might want to make sure the cable housing that snakes between the frame and swing arm is plenty long and the curves are generous.
I have a feeling your first case of mis-shift was muddy housing, cables and der. Then when the shop first cleaned everything and replaced the housing and cables, they cut it too short. Two different causes for the same symptoms.
I just wanted to say thanks to Mudpie for the recommendation on how to fix my problem. As soon as I turned the bike over I could see how tight the cable was. I did not even need to lengthen it but just needed to move it on the other side of a screw which gave it a little slack and the problem cleared right up. The reason that the problem never appeared when the bike shop guys test rode must have been the difference in our weight. The additional 40 or so pounds that I had on them just caused the frame to flex that much more at the pivot and therefore cause the cable to be tight and pull the chain out of gear. I am now ready to race again and really appreciate the comments. Thanks again.