Bike shifting by itself ?

[bjsullivan1]

Why would my bike change gears by itself? It only happens when I am climbing and I am putting a lot of stress on the drive train. Bike is about 2 years old with decent components on it. Shifts fine manually. Cables never been adjusted since new though/ Could that be my problem?

Any ideas? ???
Thanks!!!!!!!

[off piste]

2 years old is pretty old for drivetrain components, unless you seldom use the bike. I change my chainrings/chain and sometimes cassette at least twice a season as they wear. You most likley need to change something.

[Quo Fan]

Your derailer hanger could be bent. If you have ghost shifting, that is sometimes the problem.

[TheHeckler]

It may not be that the deraileur is shifting but that the chain is slipping. My bike is doing the same thing, under heavy load/climbing the chain skips off the rear cassette and the catches again. It is extremely annoying and screws up a good climb. I think it is a worn chain and cassette. I need to get a new drive train but have been to lazy. I will get it fixed in the next couple weeks.

[bike187]

also try setting the cable tension so that the rollers line up with the cassette rings exactly. if it's set up so that the rolles are only partially lined up (this would make shifting a bit off so you'd have probably noticed this if it were the case). just bring it into the shop and have them take a crack at it. after two years, you'll also probably benefit from new drivetrain bits. this is especially true if you log alot of miles or are just hard on your components. i know that i wear out stuff alot not from high mileage but from torque i put on it from being a big guy. being a masher also doesn't help the matter. i usually get at least a season out of my stuff, but that's also spread out over a few different bikes so that could be a factor that you don't have. also check and make sure the cables/housing isn't being pressured by anything else like bending around the headtube and the suspension extending the cable past housing length. if you're only noticing it now, then that's most likely not teh cause either. also if you have gripshift system, that could cause you some so called "ghost-shifting" that you didn't realize you were causing. more specifics would help us in reccomending a solution. if in doubt, just bring it to your local shop, or track down someone who knows what they're doing and offer trade of services for a sandwhich or something.

[Tim]

From the description, sounds like classic ghost shifting - caused by the rear derailleur cable hanging up so that when you bend the frame it moves the derailleur. Try cleaning and lubing your rear derailleur cable, or replacing both it and the housing.

Tim

[bjsullivan1]

From the description, sounds like classic ghost shifting - caused by the rear derailleur cable hanging up so that when you bend the frame it moves the derailleur. Try cleaning and lubing your rear derailleur cable, or replacing both it and the housing.

Tim


Thanks for the input. Not a lot of wear and tear on the chain or cassette. Bike has not been ridden hard or that much, now that I think of it. Cable is a bit mucked up though. Will clean and lube and see if there is any change. If not, off to the lbs I go.

[bdee]

If the der. adjustments don't solve it take a look at the teeth on your cassette, specifically the ones on the cogs it slips off of. The more "shark toothed" they are the more likely it's the cassette and chain. Sheldon Brown's website has some nice pix and descriptions to help you troubleshoot. Generally when everything else is lined up correctly and cable tension is right it means the cassette is worn. An old chain on a new cassette will slip in a similar fashion, and prematurely wear the new cassette. If you end up replacing parts get at least a new chain and cassette, replace the ring you use the most as well if it's shot (sheldon's site gives pix of old v. new teeth - great reference). Good luck, and if you live in Providence I'll fix it for a sandwich, or a six pack. ;D

[Ben-O]

2 years old is pretty old for drivetrain components, unless you seldom use the bike. I change my chainrings/chain and sometimes cassette at least twice a season as they wear. You most likley need to change something.

When replacing the chainrings, chain, and cassette, is there a rule of thumb on what to replace with what?

For example, I know I need to replace my front chain rings, and the chain is about 6 months old, so I'm wondering if I'd be better off replacing the chain too, even if it doesn't show much signs of wear.

[Quo Fan]

If you are spending the money to replace your rigs and cassette, then go the next step and get a new chain also, regardless of age. A worn (even slightly) chain will wear a cassette and chain rings faster.

[Ben-O]

If you are spending the money to replace your rigs and cassette, then go the next step and get a new chain also, regardless of age. A worn (even slightly) chain will wear a cassette and chain rings faster.


Yeah, you're right--better spend a little extra now. In fact, I just ordered everything. Wish me luck....