1. The most important thing about buying a new bike is to make sure it fits. The only way you'll know if the bike is right for you is to size up the bike and make sure that the bike's geometry matches your body's geometry. Ask questions and do some research.
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2. If possible, try to find a shop that will let you demo the bike on real dirt. Five minutes in a parking lot won't cut it. You wouldn't buy a car without a real world test drive, and a bike should be no different.
3. Don't belive the hype. Just because your favorite rider or best friend rides a certain bike, that doesn't mean that's the best one for you. Have an open mind and be realistic about your needs and ability.
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  1. #1
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    Common problem with Trek's?

    Are the crank's a big problem on stock Trek's?

    I broke mine today, and IronChefJim just said he broke his not too long ago...

    my question is, was it the LBS's fault or bad design?

    Me and my buddy decided to hit up the trails early today to beat the crowds that come later in the afternoon and we hit a few bunny hopping hills and two drop offs that aren't too bad and I began to notice the bike to behave and feel very odd....well, after a few more feet, I notice that my left pedal is awfully wobbly and after a few more feet, I notice the allen head screw half exposed. I stopped and tightened it up and took off again, only to have it come loose. We stopped and turned the bike upside down and really cranked it on there good and again, it would back itself out. I then noticed alot of metal shavings around the crank area, and actual crankshaft, so I decided to call it a day and limp back to the Jeep. Well, on my slow ride back, the whole crank came off. So at that point, I look into the crank and see metal shavings all inside and the crankshaft looked a bit rough. As soon as I got to my Jeep, I called the LBS I bought my bike from and they told me to just bring it by. I show up and they said that they've never seen this problem with the Trek's before? Well, after a few minutes, he did not have a replacement crank in stock, so he took one off a brand new bike and installed it and sent me on my way. While he was doing that though, he didnt seem happy and the other guy working behind the counter was kinda mumbling "wonder who put that bike together?" The bike was under warranty as I have only owned it a week and everything was free, but I was told that I should get an upgraded crank.

    Is this normal?

    The crankshaft did get some abuse from the crank wobbling around on it, is it damaged too? Should they have replaced that as well? I don't feel too comfortable going back there now with a problem with as much of a cold shoulder I was getting...and come to find out, that it was one of the owners...what should I do or handle this situation?

  2. #2
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    the crank is made of a softer alloy than the bottom bracket spindle. The spindle is probably fine.

    Regarding the problem, it may be installation error. Once the bolt backed off once, damage was probably done to the crank, so it would not stay after that.

    Some cranks may be more prone to this happening than others, but with proper installation, this should not happen, if the crank is used for its intended purpose.
    When under pressure, your level of performance will sink to your level of preparation.


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  3. #3
    Former Bike Wrench
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    1. The Bontrager cranks that usually come on Trek bikes are mostly made by Truvativ so they are at least decent quality. You didn't mention what model Trek you have so its hard to determine what level of cranks you have.

    2. Crank arms are aluminum, bottom bracket spindles (what you call a crankshaft...car mechanic?) are almost always steel which is substantially harder. There should be no damage to it from the crank arm wobbling on it.

  4. #4
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    yeah, I am a complete noob, so I do not know the complete terminology just yet

    I have a 07 Trek 4300

  5. #5
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    I also have a trek 4300, and the cranket is some el cheapo SC suntours. Truly depressing to say the least =(.
    I live in Maine and I hate lobster.

  6. #6
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    My brother started off looking at a trek along those lines. The LBS told him he was too big for that bike at 200#.

    I'm really confused why they sell bikes, that you can by in LARGE and EXTRA LARGE, yet somehow they expect these people to what, ride on the road and not go up or down hills? Or maybe they expect the bike to goto someone that is 6'4" and only 160#'s soaking wet.

    Regardless. Be happy your LBS took care of you on the spot. My experience thus far with my LBS has been a VERY frustrating and aggravating experience. I'm pretty sure you have the same chain as I did, and mine broke while I was sitting down peddling at 5mph or less!

    be smart and take the appropriate steps to take the tools to fix the chain with a few spare links.

    I listened to the LBS tell a guy with a Specialized FSB, not sure what model but when I checked they are all over like 2k, that his wheels were not that great and he should upgrade them. ????

    Seems like that is the blanket answer at these bike shops. If the part breaks, tell them that it sucks to begin with, except when they go to sell you the bike.

  7. #7
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    well believe me, I've decided to keep going back to my LBS and get my free maintence and replace things that break for 1 year.

    At first I was all about upgrading when I first got the bike, but a few guys here just said to ride it till it breaks and then go get it fixed at my LBS since it's free...and that's exactly what I'm gonna do, since they told me this bike was a perfect fit for me and it's tough as nails...I guess we're just gonna see about that

  8. #8
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    The crankset on the 4300 is not of the best quality, but they should hold up well for recreational XC riding. Based on your description, I would say that it sounds like a glitch in the installation.

    I highly doubt that Trek would sell a component on their bike which has a design flaw.
    "Winners never quit. Quitters never win. But those who never win and never quit are idiots."

  9. #9
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    The crank on my 3700 broke after about 2 months. They replaced it for me but I was still pretty upset as it happened way up in the mountains. Managed to limp back though.

  10. #10
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    Yep, its a Suntour crankset, not the Truvativ made Bontrager cranks...not the best quality and certainly below the Bontrager stuff. Still, it sounds like it was poorly installed so I'm glad that the Dealer took care of you.

  11. #11
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    I have a 2006 Trek 4500 and had trouble with the left crank coming loose. I put red locktite on it and it worked pretty good for a while but i think i'm going to have to do it again. This happened after three hundred miles on the bike (since I was new to the bike, I did beat the cranks up quite a bit).

  12. #12
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    Quote Originally Posted by Musichead13
    I have a 2006 Trek 4500 and had trouble with the left crank coming loose. I put red locktite on it and it worked pretty good for a while but i think i'm going to have to do it again. This happened after three hundred miles on the bike (since I was new to the bike, I did beat the cranks up quite a bit).

    supposedly, you might be able to get that covered under TREK's warranty.

    I sent an email to Trek, and they said to take it to any Trek dealer and have them look over the bike, and they will determine if you qualify....it's suppose to be all free according to the trek rep I emailed

  13. #13
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    I purchased a Trek 4300 early last summer and had exactly the same problem. The LBS where I purchased the bike said they've seen that problem a couple times before on the lower end Treks they sell. They replaced the crank on the left side and all was fine... then in the fall I got my Heckler

  14. #14
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    The problem isn't the crank specifically....

    but is related. The problem is the Suntour cranks are not all that, and it's an installation problem as well. While the cranks aren't bad, they aren't top end either. The big problem comes when the cranks aren't checked by the mechainic doing the set up! Crank torque should be in the 305 to 435 inch pound range! And it SHOULD BE CHECKED BEFORE THE BIKE HITS THE SALES FLOOR!!!!! The problem is few mechanics think it is necessary to haul out a torque wrench and check it!!!! Almost ALL of the 3700 to 4500 models that I've assembled this year have had LOW TORQUE on the non-drive (left side) crank arm! We have a policy at the shop that ALL crank arm bolts will be checked and torqued to spec WITH A TORQUE WRENCH. We've had very few come back with any problems. Also keep in mind that these bikes are usuing SQUARE TAPER bottom brackets and cranks. This style of crank and BB NEED TO BE CHECKED REGULARLY!!!! Even the old top end XT and XTR stuff had to be checked about every 3 or 4 rides! They do come loose unlike the newer splined and 2 piece crank/BB systems. And I've found through many years of experience that it is usually the non-drive side crank arm that will come loose.

    In the Trek line for 07 you don't get away from the square taper bottom bracket until you get up to the 6500. So if you have anything lower end than that you need to check those cranks regularly! Yes the cranks can come from the factory light on torque to begin with. But, if the LBS is doing what they should when they assemble the bike it wouldn't be a problem. And if the rider does his part and checks the cranks regularly, there probably won't be any problem at all. So guys, CHECK YOUR CRANK BOLTS OFTEN! And check em when new!!! Yeah I know, they should be good when you walk out the door of the LBS, but you never know! But if it does happen within a year it is covered under warranty. But why go through the hassle when it takes 30 seconds of preventative maintenance to PREVENT the problem in the first place?

    Good Dirt
    "I do whatever my Rice Cripsies tell me to!"

  15. #15
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    Squash-

    just bought a new bike and waiting to pick it up. Just for owner's info how can I check the crank torque? Do I need to use a torque wrench at home? Do I just check the bolts?

  16. #16
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    It's best to use a torque wrench....

    If you have one or get one if you don't. You'll need it eventually as you should check the torque regularly as I said in my earlier post. The range is pretty wide for crank bolts, 306 to 435 in/lbs. But if you are not familiar with what that range "should" feel like it can be easy to under torque the bolts and you still have the problem. And if you are like me and ham fisted, you may tend to over torque. An inexpensive beam type torque wrench with a 0 to 600 in/lb range is what I recommend, and you'll need an 8mm hex head socket as well. Just make sure that you are dealing in INCH POUNDS not foot pounds. A ft/lb wrench can be used if it's all you have, just convert in/lbs in to ft/lbs by dividing by 12. I usually torque the bolts on a square taper to 400 in/lb. No particular reason, just a nice round number I guess.

    Anyway, get the torque wrench. There are quite a few other "critical" fasteners on the bike that you should use a torque wrench on as well. Stem clamp bolts, bar clamp bolts, brake anchor bolts, or caliper anchor or caliper adaptor bolts if you have disc brakes, disc brake rotor bolts, and fork top caps, are all critical fasteners that should be torqued to spec. Both to prevent loosening or prevent stripping. IMHO it is one of the FIRST tools that you should get it you intend to do any DIY work on your bike. Just remember to USE IT!

    Good Dirt
    "I do whatever my Rice Cripsies tell me to!"

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