Changing my 21 speed- Mtbr.com
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  1. #1
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    Changing my 21 speed

    I own a 1996 trek 7000 zx 21 speed and i would like to upgrade some of the parts on the bike , i am finding that if the bike is a 21 speed i have very few options, so can i change my 7 gear cassette to a 8 or 9? Is what i have a screw on freewheel or a cassette? also i have canti brakes and hate them do they make a bracket so i can have disc rear brakes?
    Last edited by medtech; 11-07-2009 at 08:19 AM.

  2. #2
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    You'll save money by buying a new bike. It will get expensive to upgrade cassette, derailleur, shifter and chain. I doubt your frame has the mounts for disc brakes. If it did, you'd have to replace the wheels. Add it up and you'll find with the money you'd spend on all the upgrades you could have a nice new or used bike.

  3. #3
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    +1 check Craigslist or eBay for some good used bikes.

  4. #4
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    So it is all dependant on if you bike has a free hub or a free cassette. If you have a free Cassette then you are locked into your 7 gears. If you have a free hub then you can probably go up to 9 gears in the rear. Read this and figure out what you have http://sheldonbrown.com/k7.html

    There are brackets for mounting a caliper in the rear, but your bike needs the tabs in the back to mount the bracket. Also if you want disc brakes you will need at the very least new hubs that are made for disc brakes. If you want a disc in the front, again a new hub and probably a new fork if yours doesn't have a caliper mount.

    If you truelly want to keep that bike no matter what your either going to end up basically rebuilding it. You will need new wheels, cassette, derailleur, shifters, and fork if you wanted to do more gears and disc brakes. Thats going to work out to be 350 to 400 dollars for all of that depending on what you get it can be tons more or even less with used parts.

    My suggestion is to either keep that bike as a commuter and buy a new one for trail riding. Or just looking in to either getting better Canti brakes, upgrading into V-Brakes, upgrading the cassette, derailleur, and shifters. You would also be amazed by the performance increase just by getting new cables and housing for your current brakes.
    Big Foot Blue KHS XC704r

  5. #5
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    To start off, I would say that if you are planning to do all of the upgrades that you are listing, getting a newer bike, even if its used, would be much easier and worthwile.

    Using special tools, if you own them you can probably fit an 8spd cassette on. Then you must get 8 speed shifters, and probably a new rear derailleur that works with 8/9 speed.

    For the brakes. your wheels must be able to fit discs. newer wheels have bolts on them, usually 6, that bolts the rotor on to the wheel. and i imagine it would be difficult to make proper mounts and getting them perfect, because discs can be tricky..

    My best advice for you, if you dont have much money, buy a newer bike or even a brand new one!

  6. #6
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    I understand it is cheaper to get a new bike, but i have almost all the parts i would need for free , what i need to know is if it is possible to make the change. I have a new fs bike but this bike is a gem it only weights 23lbs and i like using it for climbing. but i need to start replacing a few parts.

  7. #7
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    Would need to replace rear hub as well.

  8. #8
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    Quote Originally Posted by Dremer03
    So it is all dependant on if you bike has a free hub or a free cassette. If you have a free Cassette then you are locked into your 7 gears. If you have a free hub then you can probably go up to 9 gears in the rear. Read this and figure out what you have http://sheldonbrown.com/k7.html

    There are brackets for mounting a caliper in the rear, but your bike needs the tabs in the back to mount the bracket. Also if you want disc brakes you will need at the very least new hubs that are made for disc brakes. If you want a disc in the front, again a new hub and probably a new fork if yours doesn't have a caliper mount.

    If you truelly want to keep that bike no matter what your either going to end up basically rebuilding it. You will need new wheels, cassette, derailleur, shifters, and fork if you wanted to do more gears and disc brakes. Thats going to work out to be 350 to 400 dollars for all of that depending on what you get it can be tons more or even less with used parts.

    My suggestion is to either keep that bike as a commuter and buy a new one for trail riding. Or just looking in to either getting better Canti brakes, upgrading into V-Brakes, upgrading the cassette, derailleur, and shifters. You would also be amazed by the performance increase just by getting new cables and housing for your current brakes.
    How do i know if its a free hub or cassette? and is the change to v brakes just a swap or do i need to alter my mounts?

  9. #9
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    I believe the mounts are the same, but dont quote me on that because I have never worked on Cantilever brakes. Pop your rear wheel off and match it up to the website I linked, that is the easiest way to tell what the bike has.
    Big Foot Blue KHS XC704r

  10. #10
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    The mounts are the same for cantis or Vs, you just need to run your cable directly into the V-brake noodle instead of the canti cable stop. You'll also need linear brake levers to run Vs.

    Your hub is almost certainly designed for a cassette. During that time, 8-speed was very common so it may even be possible that you have an 8-speed compatible hub but you would need to check to be sure (it would have a spacer on it in addition to the 7-speed cassette). If not, you will need a new hub (probably just get a new wheel) to go to 8 or 9 speed.

    Sheldon Brown has a lot of good info on 7, 8, and 9 speed on this link
    http://www.sheldonbrown.com/k7.html
    He also describes an option where you can modify a 9-speed cassette to fit on a 7-speed hub by removing one cog, then use a 9-speed shifter (but only get 8 -speeds).
    Warning: may contain sarcasm and/or crap made up in an attempt to feel important.

  11. #11
    ILIKEBIKES
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    Since the OP has a 7 speed out back right now will the spacing between the chain stays allow him to use an 8 or 9 speed? I know on my road bike I had to spread the stays a couple mm's.
    "The free press doesn't serve the government, it serves the governed."

  12. #12
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    Quote Originally Posted by tjchad
    Since the OP has a 7 speed out back right now will the spacing between the chain stays allow him to use an 8 or 9 speed? I know on my road bike I had to spread the stays a couple mm's.
    It's possible, but by '96 most MTBs had 135mm spacing.
    Warning: may contain sarcasm and/or crap made up in an attempt to feel important.

  13. #13
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    You may also notice with a frame designed for cantilever brakes, that the increased power of v-brakes is so strong that instead of transferring that power to the rim, the seatstays flex outward with little to no net gain unless you use a brace (looks kind of like a horseshoe).

  14. #14
    ILIKEBIKES
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    Thanks Trailville! Wasn't sure how it related to road- I wouldn't even have thought about it if I hadn't updated my old '86 Gitane road to a 10 speed cassette.
    "The free press doesn't serve the government, it serves the governed."

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