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Old 07-12-10, 01:15 PM   #1
daven1986
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Can't lock up front disc brake

Hi,

I have a road BB5 disc brake as a front brake with Campagnolo Xenon levers. I can't lock the front brake up and it doesn't seem to stop well enough.

It engages as soon as I apply force to the lever so I know that the pads are well aligned. However I can pull the lever all the way to the bar without it locking up, and with seemingly no extra stopping power after a certain point.

Do you think that it could be because I used a cheap brake cable, and it is stretching when I apply force?

What can I do to remedy this?

Thanks

Daven
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Old 07-12-10, 01:45 PM   #2
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Locking up the front wheel is a bad idea, unless the bike is in a repair stand. I never want my front brakes to lock up. It is also incredibly hard to do because of the forces involved. That said, Cheap brake cable always make a brake feel like crap. I always use a good thick(er) stainless inner cable with a lined jacket. The other problem could be some type of contaminant on the pads.
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Old 07-12-10, 01:50 PM   #3
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The quality of the cable housing is also important since it can compress when you apply the brakes. I've found this to be more of a problem than stretching of the inner cable.
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Old 07-12-10, 02:04 PM   #4
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Quote:
Originally Posted by daven1986 View Post
Hi,

I have a road BB5 disc brake as a front brake with Campagnolo Xenon levers. I can't lock the front brake up and it doesn't seem to stop well enough.

It engages as soon as I apply force to the lever so I know that the pads are well aligned. However I can pull the lever all the way to the bar without it locking up, and with seemingly no extra stopping power after a certain point.

Do you think that it could be because I used a cheap brake cable, and it is stretching when I apply force?

What can I do to remedy this?

Thanks

Daven
Daven, I encountered a similar problem with Road BB7 brakes coupled with Ultegra 9-sp STI levers. A question and a possible solution:

- Are you a bigger rider? I think stopping performance with this setup (integrated STI-type lever with road disc calipers) feels weak for heavier riders who require more force to stop.

- I remedied this problem for me by switching to BB7 MTN calipers. The cable gain is different and you get more torque from your hand to the pads. The drawback is that because of this, because the lever pull moves the pads a smaller amount, your pads will have to be closer to the disc or they will not engage completely. This means they will have to be tuned perfectly and more frequently, and the rotors will have to be kept more true. Not impossible, but it is something to be aware of. It may be easier with BB7's versus BB5's because the 7's have the inside pad adjustment.
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Old 07-12-10, 02:08 PM   #5
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A key factor in mechanical disc brakes where only one side moved is that the fixed pad must be adjusted so that it is virtually skimming the rotor. If there's much of a gap at all a lot of your lever effort goes into forcefully flexing the rotor to an S like shape as it gets pinched between the pads. And until that is done you do not have the maximum possible contact area between the pads and rotor. So check that for starters. It's actually a one click critical aspect to tuning your mechanical disc calipers.
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Old 07-12-10, 02:12 PM   #6
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No I'm a very light rider, which makes it even more annoying as at least I'd understand why it was, if I were larger!

I might try some better housing - it is cheap housing too, although I used it on my road bike calipers and they feel fine and have good stopping power. BB5s are pretty hard to get the pads perfectly close to the rotor so I'll probably stick with the road calipers, but thanks for the suggestion.

I appreciate that locking up the front wheel is a bad idea, so perhaps I should have said "poor performance from front disc brake", but alas, I cannot change the title!

Thanks

Daven

Edit: for new brake cables and outers how do these stand up? http://www.wiggle.co.uk/p/cycle/7/Tr...ng/5360011237/
http://www.wiggle.co.uk/p/cycle/7/Tr...er/5360008465/

Thanks

Last edited by daven1986; 07-12-10 at 02:25 PM.
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Old 07-12-10, 02:27 PM   #7
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A key factor in mechanical disc brakes where only one side moved is that the fixed pad must be adjusted so that it is virtually skimming the rotor. If there's much of a gap at all a lot of your lever effort goes into forcefully flexing the rotor to an S like shape as it gets pinched between the pads. And until that is done you do not have the maximum possible contact area between the pads and rotor. So check that for starters. It's actually a one click critical aspect to tuning your mechanical disc calipers.
Thanks, I have made sure that the pad is very close. I always make sure there is minimal rotor disfigurement while still making sure that there is minimal or no rubbing from the pad
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Old 07-12-10, 03:56 PM   #8
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In that case you just do not have enough mechanical advantage between your fingers and the pads. Either the caliper actuator arm is too long or the lever is pulling too much cable. A shorter actuator arm would improve the mechanical leverage. And you've already got road levers so they are not pulling too much cable. That pretty much leaves us with spongy cable and/or housing. Perhaps go with the compressionless Jagwire housing that is good for both brakes AND shifting. That would be a great first step.
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Old 07-12-10, 04:33 PM   #9
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Yeah, I am definitely going to upgrade my housing and see how that help.

Thanks again - will update with progress!

Daven
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Old 07-12-10, 04:36 PM   #10
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Originally Posted by krazygl00 View Post
...remedied this problem for me by switching to BB7 MTN calipers.....
I've never heard anyone who likes the BB5/7 road calipers. I went with the MTB calipers but it was easy, I have upright bars. I have lots of braking power with 35mm tires, it's great! My dry road stopping distance is much shorter with a frt BB7 disc and rear Weinmann 730 (with pads all the way down) compared to frt/rear 70mm Sturmey drums.
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Old 07-13-10, 12:37 AM   #11
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daven1986: You don't really say what you are comparing your lack of stopping power to. Your standard caliper road brakes? I switched from XTR V-brake to an Avid BB7 Road disc, and 160mm rotor. It was kind of OK, but I wanted more power, so tried a 180mm rotor, and it was better, but still not what I wanted. I finally put on a 203mm rotor, and now it stops the way I want. The V-brake had pretty good power, but I wanted to avoid any possibility of overheating the front RIM on my touring bike that I tow a trailer with.

Have you thought about a larger rotor? This might solve your problem.

Mr IGH: NOW you have heard of someone who LIKES a BB7 Road disc!
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Old 07-13-10, 01:28 AM   #12
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Locking up the front wheel is a bad idea, ... I never want my front brakes to lock up. ...
Locking up brakes while riding is a bad idea, true. But not having the ability to lock up means that there is braking force that you aren't using. Besides, it's all down to the surface you're riding on. IMO the stronger brakes I have, the less is the risk that I'll have to engage them in an uncontrolled panic stop.
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Old 07-13-10, 06:32 AM   #13
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Thanks, on my way into work this morning I put my hands further down the brake lever. This,I felt, gave better stopping power, so perhaps I have just been lazy and expected more power with a light touch! Will experiment again on the way home.

Thanks
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