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Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

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Old 06-20-09, 01:20 PM   #1
wezzlee
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Help Please Repairing Claud Butler Mountain Bike

Took my bike to a local shop the other day, wanting two new inner tubes, and a new chain... worth noting I know little about bike components

I was then told my 'cassette' and front cogs (?) had typically worn as with the chain, requiring new ones. All of a sudden for parts alone it mounted to around 100 before labour... I left stating I would go away and have a think about it.

I've since found I can probably source the parts for much much cheaper from namely eBay, and give the repair a go myself. This leads to my questions...

I know all the existing components are shimano, the 'cassette' is 7 rings do I need to know anything else before I buy one of these? What details would I need to get from my existing 3 front cogs to buy them? Are chains a standard size or will I need to measure the one I have? Lastly, I read I will require a chain whip and lockring (anything else?) to remove the cassette, will any ones do?
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Old 06-20-09, 01:44 PM   #2
dabac
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Quote:
Originally Posted by wezzlee View Post
Took my bike to a local shop the other day, wanting two new inner tubes, and a new chain... then told my 'cassette' and front cogs (?) had typically worn as with the chain, requiring new ones. All of a sudden for parts alone it mounted to around 100 before labour... I left stating I would go away and have a think about it.

I've since found I can probably source the parts for much much cheaper from namely eBay, and give the repair a go myself. This leads to my questions...

I know all the existing components are shimano, the 'cassette' is 7 rings do I need to know anything else before I buy one of these?
For 7-spd there are two options, freewheel, and cassette/freehub. They aren't interchangeable, so make sure you know what to get.
Cassettes comes with different ranges of tooth count between smallest-biggest, if what you get is too far away from what you have it'll change the available ratios noticeably, particularly during climbing.
7-spd cassettes are being phased out, so some searching may be required.

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Originally Posted by wezzlee View Post
What details would I need to get from my existing 3 front cogs to buy them?
Bolt circle diameter, number of carrier arms, tooth count.

Quote:
Originally Posted by wezzlee View Post
Are chains a standard size ?
Yes, but there are several sizes available. However they're usually sold with the no. of rear sprockets mentioned, which makes buying the easy.
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Originally Posted by wezzlee View Post
.. or will I need to measure the one I have?
You need to get the length reasonably right, either by matching your new to the old, or by following one of the descriptions on how to determine chain length.
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Originally Posted by wezzlee View Post
Lastly, I read I will require a chain whip?
Yes.

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..and lockring
Usually comes with the cassette.

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Originally Posted by wezzlee View Post
..anything else?
You need a splined cassette puller, chain breaker.

Do some studying at www.parktool.com, www.bicycletutor.com, and of course www.sheldonbrown.com
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Old 06-20-09, 02:16 PM   #3
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The www.parktool.com web site has detailed procedures for all sorts of maintenance and repairs on bikes, so definitely check that out. They also list the tools needed for each repair. I would *strongly* suggest buying/borrowing a good book on mountain bike maintenance and repair, such as Zinn's: http://www.amazon.com/Zinn-Art-Mount...tt_at_ep_dpi_2

If your cogs and cassette (and chain) are worn out, there's a very good chance you also need new cables and (especially) cable housing for both your brakes and your shifters.

Chain:

Be sure to get one with a reusable easy-open "master link". If you have a "7 speed" bike (rear cassette has 7 gears), a standard "8 speed chain" will be fine, such as the SRAM PC-830. Stay away from Shimano chains, as they do not come with master links.
Tools needed: chain tool to shorten chain to correct size, and to break old chain if it doesn't have a master link.

Rear cassette:

First, verify that you have a "freehub" type rear wheel, not an older "freewheel" type wheel. Next, determine the number of gears (7 in your case). Count the number of teeth in the smallest gear (probably 11, 12 or 13) and in the biggest gear (probably 28, 30 or 32) -- this determines your cassette "size", e.g. "7 speed 11-28t" means 7 gears with 11 teeth on the smallest and 28 teeth on the largest gear. Again, I'd buy an SRAM replacement on a value-for-money basis. If your wheel is designed for 8/9 speed cassettes, there should be a spacer installed inboard of the cassette -- just reuse it for the new cassette. Be sure to tighten cassette lockring to the specified torque.
Tools needed: grease, chain whip, cassette lockring tool, torque wrench, socket or other means to turn tool with torque wrench.

Front cogs:

You can replace either just the 3 geared cogs (if they are not riveted on) or the whole crankset -- you will have to figure out which is cheaper and/or better. For each cog, you will need to know the bolt circle diameter (BCD), how many mounting bolt holes, and how many gear teeth. It's important to tighten the crank bolts to the correct (high) torque value. If replacing the whole crankset, you will either have to get one that matches the spindle length of your current bottom bracket (BB), e.g. 113mm, 118mm, etc, or buy and install a BB suitable for the new crankset.
Tools needed: grease, metric hex key sockets, socket wrench, socket/hex key to match crank bolts, torque wrench, crank puller tool, wrench/socket to turn crank puller. If replacing BB: BB tool, socket to turn BB tool and to attach torque wrench to BB tool.

A great resource, especially to look up unfamiliar bicycle terms, is www.sheldonbrown.com
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