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Thread: Disc Brakes

  1. #1
    Join Date
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    Disc Brakes

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    What to do? The front left brake on my Titus mtn bike rubs on the rim (the LBS and I think). There are 2 possibilities for this, either the fork is bent or the fork was designed for disc brakes. Also, the V-brakes that Shimano used at that time were pretty lousy and Shimano changed the design after a couple of years. Also, the fork is a light weight fork most likely designed for disc brakes.

    I bought the bike in 2003 and have always had this issue with this noise. I took it back to the LBS where I bought it and they said "it's fixed" but it wasn't. I've taken it to other shops and they've "say it's fixed" and given me all kinds of reasons why I get this noise. One said I'm not putting the wheel on right, but my partner can't get it on right either!

    Anyway, the shop said it will cost about $250 for a new wheel and front disc brake. I think he said the wheel runs $120, $80 for the brake +labor. I paid about $400 for the set of wheels I put on the bike. However, that was 10 years ago.

    So, since I don't know anything about disc brakes, don't mtn bike a whole lot, but when I do I ride 20-50 miles at a time on it, what should I do?

    I'm a weight weenie, don't know what a good price for a decent mtn bike wheel is and wonder if it's smart to have a disc brake on the front and a V brake on the back, especially since it sounds like that generation of brakes weren't great anyway.

    The bike fits me well and is in very good shape so there's no need for a new one.

    Any thoughts?
    Last edited by Kathi; 04-12-2012 at 02:10 PM.

  2. #2
    Join Date
    Apr 2009
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    Quote Originally Posted by Kathi View Post
    What to do? The front left brake on my Titus mtn bike rubs on the rim (the LBS and I think). ... Also, the V-brakes that Shimano used at that time were pretty lousy and Shimano changed the design after a couple of years.
    Stop. Back up. What components are on the bike currently, and what exactly is happening?

    Reading between the lines, it sounds like you have (Shimano) V-brakes all around. The front left arm is chronically not retracting enough to pull the brake pad away from the wheel. Your LBS has repeatedly tried and failed to fix this. Correct?

    Two solutions:

    1: Buy a better grade of V-brake. The better ones really do move better.

    2: It is possible the attaching bolt is pinching the left V-brake keeping it from moving freely. The pivot boss on the fork could be a tiny bit short. Or, the mounting hardware has gotten damaged: I once encountered a cantilever brake (different brake, bit same result) that used soft metal washers under the heads of the attaching bolts. One of the bolts had been tightened so much that the pivot boss had pressed into the washer. The result was that the brake arm was getting pinched.
    Laura

  3. #3
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    Laura, I don't have the bike here, it's in the shop but the components are Shimano XT 2003 vintage. The fork says "scarab" on it, not sure if that's the brand or model. Wheelset is Cane Creek Zonos SS that I had bought in 02 for my old mtn bike.

    Bike shop guy says the brakes aren't traveling correctly when weight is put on the fork, does that make sense, so new brakes won't work. That's why he's recommending disc brakes, if the fork is bent the brakes won't touch the rim. If you turn the bike upside down and spin the wheel it spins perfectly.

    If you look at it the space between the brake and rim it looks clear. I've tried moving the brake away from the rim but as soon as I brake the noise comes right back. A friend suggested I change the way the spacers were arranged, I did, but I ended up losing one of the spacers and yea! no noise. Last year the shop that tuned it insisted on reinstalling the spacer and the noise came back.

    The shop is recommending the Mavic Crossride wheelset for $270,if I do front and back. They say they are good entry level wheels. Will I be happy downgrading my wheelset? I paid $500 for the Zonos wheelset and it has around 2,000 miles on them. Is an entry level wheelset of today equilivent to the higher end wheelset of 10 years ago? I'm a super light weight and I don't need an overbuilt wheelset. I just don't know enough about wheelsets to determine what is right for me. For my road bike I had my wheelset handbuilt, which the shop said they can do for about $650.

    Thanks for your help, I trust the shop but just need more information.



    .

  4. #4
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    I'm going to assert that the shop is "lying" about the fork being bent. They don't know how to fix the problem and their explanation is that "something's bent". If the fork really is bent, I'd want to replace the fork, not the wheels and brakes! If they keep insisting that the fork is bent, have them pull out their fork alignment gauge and prove the damage.

    Quote Originally Posted by Kathi View Post
    components are Shimano XT 2003 vintage.
    OK - so likely BR-M750 or BR-M760. Both are of the "parallel push" style. Shimano has moved away from this style because there are too many pivot points that wear and get sloppy and cause brake squeal.

    Quote Originally Posted by Kathi View Post
    Bike shop guy says the brakes aren't traveling correctly when weight is put on the fork, does that make sense, so new brakes won't work. ...

    If you look at it the space between the brake and rim it looks clear. I've tried moving the brake away from the rim but as soon as I brake the noise comes right back. A friend suggested I change the way the spacers were arranged, I did, but I ended up losing one of the spacers and yea! no noise. Last year the shop that tuned it insisted on reinstalling the spacer and the noise came back.
    OK, so the problem is that one of the brake arms isn't jumping back from the rim. Each arm has a spring that moves it back away from the rim. There are adjustments to balance the spring motion and thus keep the arms centered. However, when one arm experiences more friction than the other, they won't release to the centered position - often one arm moves while the high friction arm doesn't. The result can be a brake pad that drags on the rim causing noise. (BTW, this problem is pandemic on cheap department store bikes!)

    When you "lost" the spacer, you forced the brake arm to move farther thus increasing the return spring tension. Presumably, this was enough to make it move partially before the friction stopped it. This is an important clue as to the problem!

    Presumably the shop fiddled with the spring tension and centering adjustments while trying to fix the problem. Thus we can probably eliminate those as the cause of the problem. Lets figure out where the friction is coming from:

    Given that the brakes are Deore XT, they'll be a precision fit on the brake bosses. I doubt that they'd get crooked and stuck. However, maybe they've gotten very worn and don't pivot properly. In that case, new V-brakes would fix the problem - unless the fork bosses themselves are worn.

    Both the 750 and 760 brakes use a "Link Fixing Washer" under the head of the "Link Fixing Bolt". I can't tell exactly how the 750's use the washer, but on the '760's it is clearly a flat washer that gets pinched between the fork's brake boss and the bolt head. It would not surprise me if the washer is aluminum. (I know that Shimano used an aluminum washer on 1990 era Deore LX.) A ham-fisted mechanic may have tightened the bolt too much, damaging the washer, and causing the brake arm to be clamped too tightly. The simple fix is to replace the washer with am undamaged one - perhaps one made of steel.

    It would be a shame to spend $100's to fix a problem caused by a one cent washer!
    Laura

  5. #5
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    Hmmm, interesting thoughts. The washer was replaced last year by the mechanic that did the tune, no mechanic touched the brakes after I lost the washer. None of the washers looked damaged when I took them apart. I seem to remember the washers were a combination of materials, plastic & maybe aluminum. I will check the receipt but I'm thinking the whole set of washers were replaced.

    My partner even complains and hates it when I have to take the wheel off/on because the wheel looks centered then I start riding and bingo the brake rubs. The we have to stop and play with it until we can get the wheel turning. He also thinks I should contact the owner of the shop as I've had this problem since the bike was new.

    It's odd that 6 different people (shops) over the years haven't been able to find a solution.

    As for replacing the fork the shop was trying to find the cheapest alternative by replacing brakes and wheel just on the front. That way the brake won't be touching the rim. I'm the one who suggested doing front and back.

  6. #6
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    Jul 2010
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    Austria
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    I think I wouldn't want to have a combination of disc- and V-brake. I imagine it to be very hard to brake correctly, if you have to apply a lot of force with your right hand (for the rear V-brake) and minimal force with your left hand (for the disc brake). The pressure points will be very different between the two brakes. In a situation where you have to react really fast I imagnine it to be unsafe, especially since the disc brake will be at the front.

    One more thought: have you ever tried to replace the old V-brake with a new one?
    Last edited by Susan; 04-12-2012 at 11:58 PM.

  7. #7
    Join Date
    Apr 2006
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    Maine
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    It's hard to really get a sense of what is happening without seeing the bike, but I have another suggestion.

    The v brakes all rely on spring tension, and generally that spring tension can be dialed up as the spring wears.( that's why your caliper ends up leaning back on the rim) By being able to do that you extend the life of the brakes, and one side can indeed be different than the other... overtime that is. Because you have the 'push style' of caliper, these brakes can NOT be adjusted to give them more tension. What happens is that because of this style, the brake pads end up at an angle that hits the tires. So your only option is to replace the caliper itself.

    Although I haven't seen the bike/fork, I too, doubt that it is the suspension fork. If it were the fork, then it would sound as though the fork would need a rebuild,(new bushings etc..)but given the fact that you don't ride it a whole lot and that you are fairly light... well I would opt at replacing the caliper BEFORE I did anything.

    Lastly, I just had a bike that left the shop yesterday with a pair of wheels that I built and new brake calipers for the above problem. Of course, there's always a range of what you can spend for wheels... but $650 seems on the high side of things. ( mine were $260 with the existing hubs, and Sun Rynolite rims and DT spokes)The Mavics are indeed nice wheels, and very durable but definitely much heavier than your wheels.

    Anyway, definitely try replacing the brake caliper first, and feel free to PM if you should have any other questions. Another thing to check is make sure that your brake pads aren't worn uneven so that they can 'catch' on the sidewall of the rim. And lastly, look and feel the sidewall of the rim, is it flat, concave? Concave would mean that the brake track on the wheel is gone and you should replace the wheel.(although the LBS shop has probably already checked the above)


    http://chasecyclery.blogspot.com
    Last edited by ridebikeme; 04-13-2012 at 04:29 AM.

  8. #8
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    Quote Originally Posted by Kathi View Post
    Hmmm, interesting thoughts. The washer was replaced last year by the mechanic that did the tune, no mechanic touched the brakes after I lost the washer. None of the washers looked damaged when I took them apart. I seem to remember the washers were a combination of materials, plastic & maybe aluminum. I will check the receipt but I'm thinking the whole set of washers were replaced.
    The washer I'm talking about is on the bolt that holds the entire brake arm to the fork - not the spacers/washers that position the brake pad. It's item number 2 in the diagram here:

    http://techdocs.shimano.com/media/te...9830609090.pdf
    Laura

  9. #9
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    Ladies, thanks for your help. I went skiing over the weekend and mulled over this decision. After doing some research and comparing reviews of the 2 wheelsets it sounded like my Zonos were much better wheels. I also realized I'm not that thrilled about disc brakes and decided that if I was going to spend any money I'd rather have a wheelset built with me in mind rather than a 200 lb rider.

    Yesterday I contacted the wheelbuilder who built my road bike wheels and discovered he is now here in the Denver area (he used to be in New Mexico). He's very knowledgeable and is willing to help me out. I'm planning on taking my bike to him tomorrow.

    He explained there is any number of things that can be causing the problem, for example, the levers can be the wrong ones, so hopefully he'll get to the bottom of this. He also found it hard to believe that 6 shops couldn't find the problem.

    And, depending on the cost, I might have him build me a "little" girl's wheelset.

    I'll let you know what I find out.

 

 

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