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  1. #1
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    Rear derailer help.

    So for the first time in my riding career I built a bike up from just a bare frame, everything went well but setting up the rear derailer. I got the H and L stops set fine and the tension feels correct but when in the small chain ring the shifts are not that great. The odd thing is when in the middle or big ring it shifts fine. I'm pretty sure chain length is right as I followed the Park Tools directions, only thing I can think of is the derailer hanger might be slightly bent but I would think the problem would happen no matter what chain ring I was in and not only in the small ring. Any input on what to check would be great.

  2. #2
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    I'm not an expert, but I found on my last build that when in the small chainring, the tension on the rear der was less so the shifts weren't as crisp or quick. I assume you did the big ring, big ring and add 2 links thing to set the length of the chain?
    How much tension is on rear der when in the big/big?
    I ended up removing an additional link and it made it better....

  3. #3
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    If I assume it's a new rear derailleur, check the B screw. It should be close enough so it will keep the chain on during bumpy rides, but not so close that the pulley rubs the cassette or prevents itself from changing gears.

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    Setting the top pulley closer to the cassette stack can actually exacerbate this problem, as even less tension will wind up on the chain. For what it's worth, if these are new components, the problem is likely the hanger being misaligned, though what you are describing can also happen with a damaged parallelogram on a derailleur.

    Knowing the build list of what you used would help as well.

  5. #5
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    B screw and hanger alignment. Never trust a new hanger. I put new hangers on a flat reference surface and check for any wobble. Sometimes I can get the wobble out with judicious use of a hammer when on the reference surface, which is the cast iron table on my table saw...very heavy. Then I fine tune with a hanger tool on the bike.

  6. #6
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    Quote Originally Posted by Wheelman55 View Post
    B screw and hanger alignment. Never trust a new hanger. I put new hangers on a flat reference surface and check for any wobble. Sometimes I can get the wobble out with judicious use of a hammer when on the reference surface, which is the cast iron table on my table saw...very heavy. Then I fine tune with a hanger tool on the bike.
    Making sure the hanger itself is straight is of little concern. Dropouts are often a little skewed or paint buildup will cause the hanger not to fit flat against it's mating surface. So while your intentions are great, you're really just chasing your tail.

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    Quote Originally Posted by customfab View Post
    Making sure the hanger itself is straight is of little concern. Dropouts are often a little skewed or paint buildup will cause the hanger not to fit flat against it's mating surface. So while your intentions are great, you're really just chasing your tail.
    So your advice would be...??

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    Quote Originally Posted by bmwjnky View Post
    ........ only thing I can think of is the derailer hanger might be slightly bent but I would think the problem would happen no matter what chain ring I was in and not only in the small ring. Any input on what to check would be great.
    no, actually it usually shows on only 2-3 rings when just a tad out as it changes the travel of the parallelogram so it can often seem to work fine when in some areas and not in others.. actually having that situation gives a clue it is most likely the hanger is out.

    Quote Originally Posted by Wheelman55 View Post
    So your advice would be...??
    use a hanger tool... many times like Customfab stated a brand new frame will have interface issues skewing the hanger out a tad. Also older frames if the hanger is bent the frame probably got mildly tweaked also, even wear in the drop outs will make your wheel sit lightly off and basically make the hanger wrong to it so you'll need to realign the hanger to the wheel.
    Last edited by thomllama; 02-08-2014 at 08:14 AM.
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  9. #9
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    fully agree with custom fab and thomllama. ParkTool's DAG-2(~$70) is nice for the money and is standard issue in most bike shops. If you want some bling factor as well as a smooth, well thought out design, check out EVT's True-Arc(~$300)(or better yet, the Ultra True-Arc(~$585)). Lastly (I didn't forget about you customfab!) the HAG (~$170) from Abbey Tools is equally well thought out and nearly half the price of the EVT gauges.

    If you spend much time at all wrenching on and building your own bikes get some sort of alignment gauge. If not take it down to your LBS and have them do it for a few bucks.

    Good Luck!

  10. #10
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    Quote Originally Posted by Wheelman55 View Post
    So your advice would be...??
    Skip the hammer and surface plate treatment and just do it on the bike. Preferably with a hanger tool that doesn't have a bunch of slop in it.

    FWIW Shimano set a tolerance of +/- 4mm of hanger alignment. Good little nugget of info to have.

  11. #11
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    Quote Originally Posted by customfab View Post
    Skip the hammer and surface plate treatment and just do it on the bike. Preferably with a hanger tool that doesn't have a bunch of slop in it.

    FWIW Shimano set a tolerance of +/- 4mm of hanger alignment. Good little nugget of info to have.
    just so ya know, slop is annoying, but doesn't hurt the accuracy.. Mine has TONS of slop.. but as long as you put a little pressure in the same direction (in or out) you'll get near perfect alignment. NO question about it I'd much rather have one with a bunch less slop.. but it's not a biggy if you have a bit of patience
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  12. #12
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    Quote Originally Posted by thomllama View Post
    just so ya know, slop is annoying, but doesn't hurt the accuracy.. Mine has TONS of slop.. but as long as you put a little pressure in the same direction (in or out) you'll get near perfect alignment. NO question about it I'd much rather have one with a bunch less slop.. but it's not a biggy if you have a bit of patience
    I'm sorry but it really doesn't work that way. Taking the slop out of a poorly made or worn out tool isn't like burning an inch on a tape measure. It's a vague limit you're working with and it's not repeatable or accurate. Your methods can get you buy and might work well enough with a 7 or 8 speed based drivetrain but they really aren't accurate enough IMPO for a modern 10 or 11 speed drivetrain. The lowly derailleur hanger is the foundation of a drivetrain and it's precision is paramount to said drivetrain working at it's best.

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    well I don't have any issues.. every drive train I'e used it on has worked flawlessly.
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  14. #14
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    I would add that before you go and start bending your frame, you should understand that what you may be experiencing is extremes in chain line. What I mean is you may have the chainline off a bit. Just a suggestion but check this before anything else. Here is some good reading All About Bicycle Chainline that should help you understand it a bit better if you are not familiar with it all ready.

  15. #15
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    Quote Originally Posted by thomllama View Post
    well I don't have any issues.. every drive train I'e used it on has worked flawlessly.
    There's a few things I've picked up on in 10 years working in the industry, words like 'flawless' and 'prefect' are open to one's interpretation.

  16. #16
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    Quote Originally Posted by customfab View Post
    There's a few things I've picked up on in 10 years working in the industry, words like 'flawless' and 'prefect' are open to one's interpretation.
    hanger tool is a "reference tool" not a measurement tool.. if you set everything the same, use it the same, tension it the same all the way around the wheel you can get 99.99% accuracy.. hell you could use cardboard for the measurement if ya could get a way to mount it to the hanger... just have to understand basic geometry..
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  17. #17
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    Quote Originally Posted by thomllama View Post
    hanger tool is a "reference tool" not a measurement tool.. if you set everything the same, use it the same, tension it the same all the way around the wheel you can get 99.99% accuracy.. hell you could use cardboard for the measurement if ya could get a way to mount it to the hanger... just have to understand basic geometry..
    It is a reference tool, no hanger tool is designed to measure a hanger to tenths of a mm. But repeatably is still the name of the game. When tools develop play it becomes a guessing game of how hard to push on them to take out the slop. It's not a brick wall you can push against with confidence that it's always in the same place. That single element is where the discrepancy's are created. For every extra once of pressure you give the tool it's going to affect how much slop you've taken out and the measurement at the wheel. It doesn't seem like much at the head of the tool, but over the next ~13" it adds up to a fair bit. So next time you've got your worn out DAG-1 out see how little effort it takes to make it go from 4mm away from the rim to touching the rim, it's next to nothing. Maybe then you'll understand what I'm on about.

    I split hairs over hanger alignment so customers don't have to.

  18. #18
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    Then what should be used to measure the alignment of the hanger?

  19. #19
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    Quote Originally Posted by customfab View Post
    ...... So next time you've got your worn out DAG-1 out see how little effort it takes to make it go from 4mm away from the rim to touching the rim, it's next to nothing. Maybe then you'll understand what I'm on about.
    .....
    I total understand what you are saying, but, it actually takes quite a bit.. I use my old car points feeler gauge to get differences sometimes. "slop" isn't a floating thing in these tools,.. it's hard stops or play in the joints of the tool. When the limit of the movement is hit you can feel it quite solidly. Yes if you put real force on the tool you can flex the hanger but you'll never need to get anywhere near that much pressure to get rid of slop...

    Again, not something that's fun to deal with,.. but can still get 99% accuracy if you have patience.

    anyway... time to move on....


    Quote Originally Posted by redd4573 View Post
    Then what should be used to measure the alignment of the hanger?
    you don't "measure" you reference.. there is no set numeric measurement. you reference 4 or more spots and get them all equal.. you don't set them all at 4mm or what ever.
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  20. #20
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    Quote Originally Posted by thomllama View Post


    you don't "measure" you reference.. there is no set numeric measurement. you reference 4 or more spots and get them all equal.. you don't set them all at 4mm or what ever.
    Actually 3 points dictates a plane.
    Quote Originally Posted by thomllama View Post
    ...just have to understand basic geometry

  21. #21
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    Quote Originally Posted by customfab View Post
    Actually 3 points dictates a plane.
    ya, but..
    first off you have to hit a perfect triangle to be accurate which is near impossible on may frames, and even that is not always the best reference use as to direction to bend the hanger to straighten it if to spots you reference and above or below the high spot then you'll see a smaller variance on the tool ..you'll end up flexing it multiple times to get a final setting.. I'd rather take 6-8 points to get a better idea on exactly where it's bent and what direction to bend it so I can do it in one or 2 flexes..

    but anyway.. I'm sure people have enough of this BS...
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  22. #22
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    Quote Originally Posted by thomllama View Post
    but anyway.. I'm sure people have enough of this BS...

    I'm still enjoying it.

    I recall the days when if you wanted to check a derailleur hanger you used a Campy tool and guestimated to within 1/4 inch or so and called it good, and that was only if you worked in a quality bike shop. Lot's of shop rats wouldn't have known what a DAG was if you hit them on the head with it, and would just eyeball the hanger and make necessary adjustments with an adjustable wrench or a pair of pliers if they bothered at all. As time went by and drivetrains progressed it became pretty much standard practice to do a quick hanger alignment check before performing any drivetrain tune to avoid chasing ghosts later down the line.

    Now that we have evolved to a point where it seems they (hangers) demand the precision of a fine Swiss watch for the gears to shift optimally it's not surprising that the DAG is becoming a must own DIY tool!

  23. #23
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    Quote Originally Posted by redd4573 View Post
    Then what should be used to measure the alignment of the hanger?
    Redd...what I believe these pro dudes are saying is to put your hanger on the bike and then adjust with a hanger tool. No need to attempt to flatten the hanger off the bike as the frame or hanger mounting area might be out of true. Makes sense.

  24. #24
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    Quote Originally Posted by Wheelman55 View Post
    Redd...what I believe these pro dudes are saying is to put your hanger on the bike and then adjust with a hanger tool. No need to attempt to flatten the hanger off the bike as the frame or hanger mounting area might be out of true. Makes sense.
    yup.. probably 85% of the time I've worked on bikes with shifting issues it's a bend or damaged hanger. basically the tool screws into the hanger inplace of the derailleur and makes sure it's aligned in plane with the cassette/wheel.
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    Thanks for all the tips, for some reason I never go notified of the replies in this thread. The hanger was bent, no one local had one so I put it in the shop vice and got it almost perfect again. Doing this and shortening the rear cable from the frame to the derailleur has got it working like it should. The jockey wheel is almost touching the big cog so it probably needs to be replaced to be 100% correct but its working for now.

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