Trouble with chain staing in gear on TREK 6000. please help?

Question

the problem i am having is that my chain is having troubles staying on the sprockets on the rear tire. this problem occurs when i attempt to accelerate quickly or pump up a hill. or flat ground for that matter. i took the bike to the local trek dealer and after about 20 minutes the guy said nothing was wrong with the bike at all. he made an adjustment to it and away i went. not more than 2 blocks later i went to really amp up my speed and sure enough, the chain fell from its higher gear and made a god-awful sound which is really starting to p**s me off as the chain dropped to the lowest sprocket. for one, it is bad for my bike im sure. two, i alsmost biffed it hard when my body threw itself forward when there was absolutely no tension on the chain. and three, the guy at the "trek dealer" said there was nothing wrong with the bike. i say bull#$%^. if there wasnt anyhting wrong, i wouldnt be writing this post. so with that said, what is the problem, and how should i go about fixing? thnx

Answer 1

What your are talking about is called auto-shifting. Eliminating that is part of adjusting your derailleurs. The two best web pages on how to do that are http://sheldonbrown.com/derailer-adjustm... from the late, great Sheldon Brown and http://www.parktool.com/repair/byregion.... from Park Tools.

HTH

Answer 2

Take the bike to another shop and have the rear derailleur cable replaced. Make sure that the new one is properly tightened and have the shop check the condition and routing of your shifter cable housings. Particularly the rear housing which should be routed INSIDE the front brake caliper (assuming your bike has S.T.I. shifters) so the caliper does not damage the housing when you turn the bars.  Also have them make sure that your shifters are working properly. You may need a new chain and cassette so have the chain and cassette checked for signs of wear or damage. Once everything is done ride the bike at the bike shop to make sure it is fixed before leaving. The only sound you should hear on a good working bike are the tires rolling on the road and the wind in your hair. Good luck!

Answer 3

OK sounds like a derailleur adjustment. Look at the rear derailleur. You'll see that where the cable attaches there is an adjustor. Turn it clockwise to make the cable looser and anticlockwise to make it tighter. This will allow you to finetune your derailleur so that the chain won't climb onto another gear under load. Check out the link for pictures.