how do i fix my bike the gears keep switching by themself?

Question

the gears switch on my bike with out me switching them whats wrong and how can i fix it

Answer 1

Sounds like ghosts...

You didn't state what kind of shifters you have, so it's hard to determine. If ya have cheapo thumb shifters you may need to tighten a screw or bolt that goes through the assembly. If it's too loose, the ratcheting mechanism may not catch. If it's too tight it will be hard to shift. It's just a guess without more info.

Answer 2

Need a bit more information to help you best, but check out www.parktools.com and click on "repair help". Problems in the rear or the front have different causes usually.


If you're on a full suspension bike, it's possible that you're getting "ghost shifting" due to improper cable housing length or binding. When you bounce, the change in ride height can pull on the cables and make the derailleur shift on some bikes if they aren't set up properly.


If you're on a hardtail or a road bike, you probably just need to adjust the cable tension. The Park site can show you how with good photos. DON'T mess with the screws on the derailleurs yet. Once those screws are set up on installation, they don't come undone and they shouldn't be messed with unless you have a reason. Cable tension is where you start. Look for bent/crushed cable housing, too....if the inner cable can't move freely, you can't shift and pedal trouble-free.


Other things to look for are the condition of the chain and the gear teeth. If your chain isn't lubed well, or worse, if it's rusty and caked with grime, the links may get stiff or stick and not conform to the gears while you're pedaling. Then, they lift up and cause a misshift. Clean it and lube it with a good bicycle chain lube. Check out the front and rear gears for any teeth that might be bent or broken off. Look between each gear in the back to see if any grass or whatever is tangled up in there...that can cause the chain to ride high or lift up, too.


If all checks out, then it might be your shifter. Be careful if you open it up because most of them don't have any spare parts available.

Learning to work on your bike is fun, but while you're learning you might just take it to a shop and ask if they'll let you watch. Some will.

Answer 3

You need to index your gears. On both the front and rear derailiers you will have + and - screws, for top and bottom gears. Start by turning the lower screw (-) until the chain moves smoothly onto the lower ring. Now turn the + screw until the chain moves onto the upper ring. Make sure your chain runs smoothly. Look at this site for how to guides:

www.parktools.com

Luck

Answer 4

M R has it right. Sounds like you have a simple lever shifter that needs the tension tightened. Most indexed shifters won't allow the gears to shift themselves.