Mountain bike gear replacement?

Question

I have a 21 speed mongose mountin bike. Recenly the rear sproket teeth broke off so some of my gears don't work like 5th, 7th, and 4th. I have a new one that I can put on it but I don't know how to take it off and put the new one back on. (This is one of those cheep walmart bikes so its a simple design).

Thanks for the help!

Answer 1

bring it to a bike shop, it's not worth potentially ruining your bike.

Answer 2

I'll have to go with billy on this one, with one small but important addition, as sfr notes, have them replace the chain as well. He's right on the money about them 'wearing together'. What we don't know is if you have a cassette or freewheel style cog body. This is critical as the parts are _completely_ incompatible with each other.

If you have no experience at making such repairs, you have two options. Take it to a local shop, where they will replace the cogs and chain, as well as calibrate the system so it shifts properly, or you can buy the tools and do it yourself. In the end,  it will probably cost you more to do it yourself, though for future repairs you won't have to pay for labor. If you go to a small local bike shop, there is a high likely hood they will let you watch them repair it, so you can learn, but going in blind with no experience will land you in the shop anyways.

If you have a decent mechanical aptitude, try www.sheldonbrown.com for step-by-step instructions, as well as the tools you'll need.

Answer 3

Taking a cassette off requires a cassette removal tool, a big adjustable wrench and a chain whip.

There is no standard for cassette removal tools.  Park Tool makes an entire line of the things to fit all the different cassettes made.  Best thing to do is take your rear wheel to your bike shop and ask them which tool you need.

You should read the Park Tool Page on replacing cassettes before you start this project.  Here is the link:

http://parktool.com/repair/readhowto.asp...

Keep in mind, shifting may be rough if you only replace the cassette.  The cogs of the cassette, chain and chain rings all wear in together.  If you replace one part of the drive train, it may not mesh well with the old, worn components.  Be ready to replace the chain and chain rings if shifting is rough and/or unpredictable.

Hope this helps.