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  1. #1
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    Need help!! Just picked up a Trek 7.5fx, not happy-it has a problem with front der...

    I picked up a Trek fx 7.5 the other day, it seemed as if there was a derailer adjustment issue. I noticed that when I was in the middle ring in front, the rear 4 largest gears caused a rubbing noise on the derailer in front. The strange part is that I always thought that bikes would sometimes make some noise if you were on the extreme cross chain situations, on my bike those situations seemed ok though. I brought it back to the shop and it seemed like the mechanic was struggling to get it quiet. He mentioned that the new 2011 design on the deore derailer had tighter tolerances. The strange part is that my brother got the same bike on the same day, built by the same mechanic, and has no issues! The mechanic finally got it to work normally, but it seems that the adjustment is still a little off and drifts. I looked a little more carefully today, and it seems like the front gears have a little runout in them, maybe the thickness of 2 dimes. I have a feeling that this is what is eating up his tight tolerances and causing the rubbing. Is it normal for the gears to have a little runout in them? Shouldnt they spin perfectly straight? Did any of you ever hear of anything like this? I'm really upset, I was looking forward to this bike so much, now I feel like I made a bad decision. I'm taking it back again tomorrow, is there anything I can suggest or request from them? Any suggestions on what it might be? Thanks.
    Chris

  2. #2
    Constant tinkerer FastJake's Avatar
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    Did you just buy it brand new? The FD should not rub, except maybe when in the extreme combinations. It should definitely not rub in four of the gears. Take it back, tell them they need to fix it.

    If the chainrings are actually bent as you describe, they could be defective and need replacing.
    Why "derailer" is the correct way to spell the gear-change mechanism: sheldonbrown.com/derailer.html

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    Jake, it's a brand new bike with about 15 miles now. That's why I'm so upset about this. My daughter has a $230 diamondback with much lower end components, and hers shifts perfectly, my wife has a $350 Univega, also with lower components that also shifts perfectly. I also, unfortunately, just sold my 13 year old Raleigh M-80 that was in showroom condition, never had a problem. Now that I spent close to $1,000 for a bike I'm having all kinds of problems. I definitely expected much better out of this bike, and to say the least, I'm disappointed. Thanks for your input, I think I'll point out the chainring situation tomorrow, maybe the mechanic never saw the problem. Or maybe they tried to avoid changing parts by "adjusting" the problem away.

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    It could also be a mechanic that is unsure of the adjustments needed to fix the problem. He is correct about the front deraileur has been changed and is a lot more sensitive to rubbing both inner and outer cage plates if not set up right. The cranks need to be torqued to about 30 ft. lbs. possibly loose from reassembly or from factory. F/derailur should be parallel to chain rings and with the chain in small ring in back and midde ring front the chain should just barely clear the outer cage plate of the front deraileur. Then adjust cable tension to get this to happen. Next check inner ring adjustment as well in the same rear cog, and can probably tighten up this adjustment as well, then back to middle and check cable tentio again. That should get your new ride fixd.if you need more help go to Park tool.com

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    Let's keep it as simple as possible. it's a brand new bike, and the owner is entitled to have a bike that works as intended. If the bike's FD cannot work correctly - by design - than the buyer should have been told that's the way it is.

    Actually, I don't think there's any problem, except possibly for sloppy assembly and adjustment. (with the understanding that there is some degree of crossover limitation). The OP doesn't have to go to any site, check crank torque, or FD alignment. That's not his job, it's the job of the shop that sold the bike.

    It's very simple, new bikes should be delivered in top working order. Anything less than that is unacceptable.
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    Thanks for all the info. FBin NY, I agree with what you said, I just bought a new bike and it should be perfect. I think Nwbikeman was just trying to give me different possibilities at this point. I am definitely not going to mess with it at this point. I honestly don't think it is incompetency of the mechanic though. He seemed to have his stuff together. And like I said previously, he assembled and adjusted my brothers (same bike) perfectly. I think there is some kind of malfunction, that's why I was asking if there is a certain amount of "normal" runout on the chain rings.
    Thanks again guys, I'll let you know how it pans out after tomorrow.

  7. #7
    Senior Member skilsaw's Avatar
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    My ultegra brifter for a 50/39/30 triple crank clicks 4 times to give me 5 positions.

    50 > trim click > shift click > 39 > shift click > trim click > 30

    Try clicking your left shifter very gently and listen/feel for the trim clicks. These positions prevent rubbing.

    I know your shifters are different than mine, but maybe they work the same.
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  8. #8
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    Quote Originally Posted by skilsaw View Post
    My ultegra brifter for a 50/39/30 triple crank clicks 4 times to give me 5 positions.

    50 > trim click > shift click > 39 > shift click > trim click > 30

    Try clicking your left shifter very gently and listen/feel for the trim clicks. These positions prevent rubbing.

    I know your shifters are different than mine, but maybe they work the same.
    flatbar shifters have no trim function. At least none that I've heard of have a trim function.

    most likely case, the FD cable needs to be tightened just a bit.
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    Mister Bleak! mconlonx's Avatar
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    Take it back to the shop. Explain your displeasure, try not to get emotional. Suggest that chainring/crank runout may be out of tolerance, especially with the new der design, and that perhaps they could see if Shimano would replace the crank under warranty.
    Quote Originally Posted by Six jours View Post
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    Brand new bike? Purchased from a bike shop? Don't be upset, just take it back to the shop.

    You pay a hefty premium when you buy a new bike from a shop (versus a used one off C/L or whatever). Part of this premium is having someone to stand behind it. You paid for that service, I would use it.

    Once you start tweaking on stuff, if you are unsure what you are doing, you could just make it harder for the bike shop to sort out.

  11. #11
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    Quote Originally Posted by up4speed View Post
    I picked up a Trek fx 7.5 the other day, it seemed as if there was a derailer adjustment issue. I noticed that when I was in the middle ring in front, the rear 4 largest gears caused a rubbing noise on the derailer in front. The strange part is that I always thought that bikes would sometimes make some noise if you were on the extreme cross chain situations, on my bike those situations seemed ok though. I brought it back to the shop and it seemed like the mechanic was struggling to get it quiet. He mentioned that the new 2011 design on the deore derailer had tighter tolerances. The strange part is that my brother got the same bike on the same day, built by the same mechanic, and has no issues! The mechanic finally got it to work normally, but it seems that the adjustment is still a little off and drifts. I looked a little more carefully today, and it seems like the front gears have a little runout in them, maybe the thickness of 2 dimes. I have a feeling that this is what is eating up his tight tolerances and causing the rubbing. Is it normal for the gears to have a little runout in them? Shouldnt they spin perfectly straight? Did any of you ever hear of anything like this? I'm really upset, I was looking forward to this bike so much, now I feel like I made a bad decision. I'm taking it back again tomorrow, is there anything I can suggest or request from them? Any suggestions on what it might be? Thanks.
    Chris
    First, I agree that your bike should work properly. However don't be so quick to rush to judgement on the mechanic. There are many variables that he has to work with to find the proper combination. Be a little patient and work with him, not against him. Your problem is a cable issue...most all derailer problems are. Either the cable isn't tight enough or, since this seems to be variable, you cable housing has a problem like a ferule that hasn't seated properly.

    The chainrings on all of my bikes aren't perfectly straight. Each has a slight wobble to it especially after having ridden them for many miles. It's (almost) normal. A millimeter (thickness of 2 dimes) seems a little excessive. Mention it to the mechanic.

    If nothing else, ask, nicely, to have another set of eyes look at the bike. Maybe they'll see something that the first mechanic missed. Be patient and be nice.
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    if the crank arm spider has some run out remove crank and put it on all 4 different position. i think these are square taper cranks. anyways the 7.5fx from trek is a pretty good bike and very easy to adjust. if has the shadow style rear derailleur then b tension adjustment is critical

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    Thanks for all the responses. I just got back from the shop. It looks like the FD needed a little tweaking again, mostly cable adjustment. It seems like at the cross chained situations at both extremes, I get an intermittant and very slight rubbing. I know that if the chainrings were perfectly straight, this wouldn't happen but the mechanic at shop said that the slight wobble I have is "normal". I looked at other bikes in the shop and they were the same as mine. The weird part is that the one extreme cross chain situation, the chain rubs on the inside of the derailer, and on the other extreme, it seems to rub on the outside. It looks like the FD needs a wider range of movement on the range of motion at the extremes. I have to assume that if this was adjustable, he would have taken care of it. Maybe this bike is different than what I'm used to because the extra gears? I think it is working somewhat normal now, what do you guys think? I am going to put a few hundred miles on it, and get it tuned up after it breaks in for a while. I have to imagine that it can be adjusted more accurately then.
    Last edited by up4speed; 04-16-11 at 10:20 AM.

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    Obviously you don't want to crosschain your chainrings and the cassette (biggest-biggest or smallest-smallest). In addition to chain rub, crosschaining will kink the chain and subject the teeth on the rings and sprockets to more wear, biggest-biggest will also put a lot of strain on your rear derailleur pulley, and smallest-smallest will make the chain too slack. Just don't do it.

  15. #15
    DRF aka Thrifty Bill wrk101's Avatar
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    +1 Don't cross chain, that's bad for any bike.

  16. #16
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    The mechanic is giving it to you straight about a bit of runout being normal on cranks. These aren't made to aerospace tolerances so all have some degree of runout. Also flexing of the crank, spindle, and frame will cause the top of the chainring to move out a bit under heavy pedal pressure.

    All that is factored into the width of the FD cage, so it should be possible to trim it for zero load in all normally used combinations, though you can expect some rubbing when crossed over to some degree, ie. the first on or two crossed over sprockets.

    They could widen the cage to accommodate greater changes in chain angle, but that would worsen shift response so they focus on best overall performance based on the assumption that you wouldn't ride crossed over, except for very short intervals. Some systems have trimmable FDs, notably Campagnolo, that allow you to fine tune the FD position as you ride, but most indexable front systems don't.

    As long as you get good, shift performance, and no rub in the commonly used gear combinations, your bike passes muster.
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  17. #17
    Senior Member Retro Grouch's Avatar
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    Quote Originally Posted by wrk101 View Post
    Brand new bike? Purchased from a bike shop? Don't be upset, just take it back to the shop.

    You pay a hefty premium when you buy a new bike from a shop (versus a used one off C/L or whatever). Part of this premium is having someone to stand behind it. You paid for that service, I would use it.

    Once you start tweaking on stuff, if you are unsure what you are doing, you could just make it harder for the bike shop to sort out.
    ESPECIALLY FRONT DERAILLEURS!

    There are several front derailleur adjustments. They have to be done in order because each one affects the subsequent adjustments. If you're not pretty sure of what you are doing - do your bike mechanic a favor and take it back to him before monkeying with it.

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    Thanks again, I guess I'm all squared away now. Time to ride and enjoy the bike!

  19. #19
    Constant tinkerer FastJake's Avatar
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    Glad to hear you got it fixed. As everyone has said, don't use the cross combinations! Bad for your chain, sprockets, derailers (if they rub). Bad for everything! Other than that enjoy your new bike.
    Why "derailer" is the correct way to spell the gear-change mechanism: sheldonbrown.com/derailer.html

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