Trouble with Shimano "MegaRange" 14-34T Freewheel- Mtbr.com
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  1. #1
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    Trouble with Shimano "MegaRange" 14-34T Freewheel

    Hey ya'll,

    I recently bought a used Raleigh M20 mtb off craigslist as a present for my son-in-law, and spend some time and a little money fixing it up. In the process I noticed the freewheel had this huge 34 tooth granny gear. I really liked it, and decided to buy the same freewheel for my Giant Rincon SE. I put it on, along with a new chain, only to discover that the derailleur jockey wheel rides right down on the big gear, and the cage rubs badly on the side of the big gear when it's on the second gear down. Needless to say, it's not rideable this way. I compared my son-in-law's bike with mine to see what the difference is that makes it work on his bike, and I notice that, for one thing, his jockey wheels are much bigger than mine. I have a Shimano Acera RD with trigger shifters, and his bike has a Tourney RD with twist-grip shifters.

    I'm a bit of a newbie with bike mechanics, so I'd appreciate any advice. If I get a new Tourney rear derailleur like his, will it work with my shifters? Also, his chainrings are bigger than mine if that makes any difference to this problem...

    Thanks in advance!

    --acorn

  2. #2
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    There is a adjustor called the b-screw. This sits on the cylinder of metal around where the derailleur is screwed to the frame. It purpose is to adjust how the jockey wheels sit, and to move them closer or further from the cassette. Screwing this in clockwise will be what you need to do to solve the problem
    Rimmer - "There's an old human saying - if you talk garbage, expect pain"

  3. #3
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    Alex,

    Thanks for the reply. I'm not sure there's enough screw for the adjustment needed. Besides that issue, though, is the other issue - when the chain is on the second-biggest gear, the cage rubs on the side of the big gear badly... I can't see any way to adjust for that. As I said, the rear derailleur on the other bike has a much bigger jockey wheel, so the cage clears the big gear on it...

    I may be wrong, but I think the only way to make this work is a different derailleur. Please correct me if I'm wrong, and if I'm right, I'd like to hear suggestions for a cheapish derailleur that will work with this freewheel.

    thanks again,

    --acorn

  4. #4
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    A bigger jockey wheel will actually do the opposite......make it harder for it to clear.

    You will need to take it to a shop to get them to look at it. Its very hard to diagnose these problems over the net. You may not need a new derailleur after all - but it may just need some adjustment.
    Rimmer - "There's an old human saying - if you talk garbage, expect pain"

  5. #5
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    Actually, as I noted, the Raleigh, with the Tourney derailleur clears it just fine. The large jockey wheel actually causes the metal cage to clear the big gear when it's on the second. I may take it to the shop, but I live in the country and it's very inconvenient to get there when they're open. So, like a true farmer, I'm always trying to do it myself

    Thanks again,

    --acorn

  6. #6
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    Yes, I realise the tourney does it, just that your supposition that its the large wheel that is making it do so is not the reason.
    If you go to the Parktool website, they have some technical documents, one of which is instructions on how to tune a rear derailleur. This my well help you to solve the issue without outside help.
    Rimmer - "There's an old human saying - if you talk garbage, expect pain"

  7. #7
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    Thanks again Alex It's not actually a supposition, but a fact that the larger wheel is what causes the metal cage to clear the largest gear in this instance (when the chain is on the second-largest gear). I have been to the website as well as many, many others, and, although I do realize that there may be some adjustment I can do to get the jockey wheel to clear the big gear when it's on that gear, there is no adjustment possible to get the cage to stop rubbing on the big gear when the chain is on the second-biggest. As you said, it's hard to describe without you being able to see it.

    I would post pictures of what I'm talking about, but time is short for me this time of year, getting ready for the holidays and family to arrive, and also end of year projects at work. For now, I have put the old freewheel back on, and the bike is again rideable - I'll revisit this later

    Incidentally, in addition to my other issues, the new freewheel seems to be warped or something. When I spin the back wheel, it wobbles side-to-side, even when it's not turning. I'm assuming the freewheel mechanism itself is defective, and have sent it back for exchange (purchased from Amazon).

    I do appreciate your continued feedback, thanks again!

    --arthur

  8. #8
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    Quote Originally Posted by acorn View Post
    Incidentally, in addition to my other issues, the new freewheel seems to be warped or something. When I spin the back wheel, it wobbles side-to-side, even when it's not turning. I'm assuming the freewheel mechanism itself is defective, and have sent it back for exchange (purchased from Amazon).

    Your new freewheel will do the same thing, the wobble is due to imperfections in the machining of the hub. Totally normal and no problem.

  9. #9
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    J.B. Thanks for your input!

    Obviously, I have a lot to learn. I have 8 bikes here at the house, ranging from walmart brands to entry level bike shop brand bikes. None of them do this. The old freewheel, which I have put back on, does not do this. I guess the imperfections in the machining of the hub are why I'm sending it back, and if the new one does it, I'll send it back too. As much as it wobbles, there's no way it's ever going to shift right. It's cheap, for sure, but it's not free, and I'm not paying for something that doesn't work at all The freewheel, by the way, came with like a 4.5 out of 5 average review out of near 40. There were at least a couple which said they ended up needing a new derailleur to make it work, which is fine. The wobble isn't though. It's a big wobble


    Thanks for the input guys, keep it coming please

    --acorn

  10. #10
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    Quote Originally Posted by acorn View Post
    I have 8 bikes here at the house, ranging from walmart brands to entry level bike shop brand bikes. None of them do this.
    Freehubs (cassette) are not as susceptible to this problem and generally run straight, but IME 9 out of 10 freewheels have a noticeable wobble when the wheel is coasting, and a lot of them wobble severely. It is because the threads are not cut squarely to the axle plane.

  11. #11
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    I'm sure if i scrutinized them better, I'd notice a wobble in all these bikes, for sure. But not what I'm seeing in this one. I'm sure you're right. The threads being not cut squarely is exactly what the issue is I'm sure. Completely agree.

    One of these days, when I'm not trying to supply a family of 6 that live in two different states (long story) with 2 different sets of bikes that work properly, I'll upgrade my own to a freehub/cassette, a better front fork, better wheels, and all kinds of stuff. As it is, I'm just trying to do the best I can with what I have. Except this, I thought I'd give myself a LITTLE upgrade. Sheesh heehhee

    --acorn

  12. #12
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    You can pull the derailleur back I used string to tie the cable to the fender strut. I've seen others use a spring tied to a rack. It may work if you remove the B tension bolt and put it in backwards so the bolt side hits the dropout stop this gives it about 5mm more range or use a longer bolt it is a standard metric size. Megarange freewheels work best with megarange derailleurs and they are only $12. Check out my posts on 40 and 52 rear cogs.
    "Dish is illogical." Spoke of Vulcan.

  13. #13
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    OP, try the B-screw thing. It should cause your derailleur to sit a bit further out in the second-largest cog too.

    You can try a longer screw if you have to. It's probably a normal metric diameter and pitch, and your local hardware store will have some. I guess the above poster already mentioned this.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  14. #14
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    Thanks guys!

    zerodish - I'm gonna look at getting a new derailleur for sure I think, I'll check out your posts

    AndrwSwitch - I think the B-screw ideas would work for the jockey wheel running right down on the cogs, but if it rides anymore outboard on the 2nd gear it's gonna tend to shift when I don't want it to I'm afraid.

    Thanks again guys, I'll let you know how it turns out

    --acorn

  15. #15
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    The B-screw shouldn't effect the lateral position of your derailleur. It just gets it to travel a little further away from the rear axle.

    Good luck!
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  16. #16
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    Quote Originally Posted by acorn View Post
    Thanks guys!

    zerodish - I'm gonna look at getting a new derailleur for sure I think, I'll check out your posts

    AndrwSwitch - I think the B-screw ideas would work for the jockey wheel running right down on the cogs, but if it rides anymore outboard on the 2nd gear it's gonna tend to shift when I don't want it to I'm afraid.

    Thanks again guys, I'll let you know how it turns out

    --acorn
    This is a typical size for that screw:
    - Various Manufacturers Stainless Socket Cap Screw 4 mm x 20 mm - Harris Cyclery bicycle shop - West Newton, Massachusetts
    - Derailer Adjustment

    I think I had a M4x16mm screw that I used on mine:
    - DSCF1331


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