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Old 06-12-10, 04:32 AM   #1
Lasvegosaurus
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Vintage/Classic Bianchi - Help me fix it or is it ruined?

I mustíve hit my bike while parking my car because the front brake is out of place so my front wheel cannot spin freely. I donít know the correct terminology so Iím going to call that whole part including the brake pads and mechanism that push them to the rim the ďbrake assembly.Ē The brake assembly is mushed to one side. I removed the front wheel because it couldnít spin freely. Is there any way to fix/replace this?

Iím going to take her to the shop on Monday, I just wanted to post here to see if there was any hope for my baby, sheís my first road bike and I didnít even get to name her yet

Here is an overall view

Here is a top-down view, as you can see the brake assembly is not aligned correctly with the fork.

Hereís the left side all crunched up

Compared with the right side, which is pulled apart
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Old 06-12-10, 04:59 AM   #2
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use a 5mm hex wrench to adjust the front bolt.
tutorial http://bicycletutor.com/sidepull-caliper-brakes/
u don't really need the centering tool in the video.
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Old 06-12-10, 11:48 AM   #3
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There's more damage than that. The bolt for the brake caliper is clearly bent. That's why the one side of that spacer washer is crushed and there's a gap on the other side. It's also quite possible that you bent the caliper arms at the same time since this is where the pressure to bend the bolt would have come from.

It may be possible to remove the caliper from the bike and take it all apart and straighten the bolt if you're handy with this sort of thing. But if the caliper arms are also bent then alloy parts should not be bent back into place. Aluminium has a poor fatigue cycle from being bent a gross amount. Often when bent badly if you try to straighten the parts back they will crack from the adding up of the successive stresses. And if the part did not crack apart then it may be on the verge of doing so. And since this is your front brake it would be prudent to replace the caliper altogether if the arms are bent just because you would not know how close to sudden and total failure they are if you straighten the alloy and it doesn't actually snap.

It's hard to tell from your pictures if you did bend the arms. But you certainly did bend the center pivot bolt. To check the arms you'll want to compare the front and rear calipers and see if the arms are still both the same shape. If by some lucky chance you did only bend the bolt then there's no big issue with trusting it once straightened since steel doesn't suffer from the same issues with fatigue. As long as you can strighten it back up without leaving any kinks or other damage it would be fine to re-use.
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Old 06-12-10, 12:07 PM   #4
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Bent bolt. Unbend it.

Are the forks bent?
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Old 06-12-10, 01:17 PM   #5
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bent bolt = replace bolt (from experience any bolt that was bent when I try to unbend it it snaps, especially small bolts up to 10mm diameter)
Replacing a bolt can be creative since many have all sorts of lengths cylindrical surfaces of various diameters, but it can be done easily by grinding it to dimension, and redo all surfacing on a lathe or hold the bolt in a drilling machine and file it while revolving (an improvised lathe)
Good bolts have grades:
12.9 = 12 (1200MPa breaking point of material) .9 (90% of 1200MPa = yield point)

Try to get 8.8 or higher (10.9). If the bolt is too hard (12.9) it will be impossible to tightening without damaging something else (it must be super tight) also standard washers do not help. - These are ISO grades, not ANSI
For clearing that out check ANSI grades of bolts: http://en.wikipedia.org/wiki/Screw

But if the bolt is not seriously bent, try leaving it like that. Do not try to straighten it, it will snap (most probably the bolt on that brake is a hardened one, like 8.8, and not mild like 4.6. 8.8bolts are prone to brittle failing and not as much to bending, so it's prone to break at bending it out)
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Old 06-12-10, 01:35 PM   #6
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If the rest isn't damaged, get a nice pair of Suntour Sprint 9000 brake calipers or similar, and call it a day.

-Kurt
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Old 06-12-10, 01:37 PM   #7
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Quote:
Originally Posted by Asi View Post
bent bolt = replace bolt (from experience any bolt that was bent when I try to unbend it it snaps, especially small bolts up to 10mm diameter)
Replacing a bolt can be creative since many have all sorts of lengths cylindrical surfaces of various diameters, but it can be done easily by grinding it to dimension, and redo all surfacing on a lathe or hold the bolt in a drilling machine and file it while revolving (an improvised lathe)
Good bolts have grades:
12.9 = 12 (1200MPa breaking point of material) .9 (90% of 1200MPa = yield point)

Try to get 8.8 or higher (10.9). If the bolt is too hard (12.9) it will be impossible to tightening without damaging something else (it must be super tight) also standard washers do not help. - These are ISO grades, not ANSI
For clearing that out check ANSI grades of bolts: http://en.wikipedia.org/wiki/Screw

But if the bolt is not seriously bent, try leaving it like that. Do not try to straighten it, it will snap (most probably the bolt on that brake is a hardened one, like 8.8, and not mild like 4.6. 8.8bolts are prone to brittle failing and not as much to bending, so it's prone to break at bending it out)
You are wildly overthinking and overanalyzing this. If the mounting bolt is bent, a Shimano replacement bolt can be ordered that will be the right configuration, right material and right size.

Then too, bicycles don't require exceptionally high grade fasteners and relatively ordinary ones do fine.

Quote:
If the bolt is too hard (12.9) it will be impossible to tightening without damaging something else (it must be super tight)
This makes no sense at all. The tightness is a function of the torque you apply, not the grade of the bolt you happen to use. Also, there is nothing in any bike brake that has to be "super tight". The torque recommendations for every bolt in them are quite modest.
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Old 06-12-10, 02:04 PM   #8
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Bent bolt. Unbend it.

Are the forks bent?

I would like to see the pics of the fork and front wheel. I can't really understand how your car only hit the brake caliper (assemebly) and bent it. It sounds to me like this is better left to the shop to correct. unless you have a buddy who does his own work and look at it.

I hope the fork and frame are OK that looks like a nice Bianchi
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Old 06-12-10, 05:30 PM   #9
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Originally Posted by HillRider View Post
You are wildly overthinking and overanalyzing this. If the mounting bolt is bent, a Shimano replacement bolt can be ordered that will be the right configuration, right material and right size.

Then too, bicycles don't require exceptionally high grade fasteners and relatively ordinary ones do fine.


This makes no sense at all. The tightness is a function of the torque you apply, not the grade of the bolt you happen to use. Also, there is nothing in any bike brake that has to be "super tight". The torque recommendations for every bolt in them are quite modest.
Grades start from 2 to 12 with rigidity from 40% of braking point to 90% of braking point. Low grade: 2 to 5 should be avoided, these are low quality that fails at moderate tightening. 6-8grades are standard and in bikes most of the bolts are 8.8 specifically. The second number after dot shows rigidity. And 90% out of 1200MegaPascals is a lot of effort. The idea is that a super-rigid bolt will not stretch much under tightening effort, and a bolt must stretch when it's tight so that it apply elastic force on the assembly but the friction in the thread is greater than the elastic force. (do be precise, the angle of friction is grater than the angle of the force applied).

To be specific, a 12.9 bolt requires tightening close to 90% of braking point to prevent loosing. At 90% of 1200MPa any washer will be crushed so as the mating thread. 12.9 bolts are used in assembly of roll-cages in racing cars, also some other crucial places where all the parts are chunky and can withstand sunch a force.
A medium bolt 8.8 is more elastic and require less force to be installed correctly, and at this less force everything holds up.

This is plain material science, along with some bolts theory. The torque needed for a bolt is determined by the bolt along with he elasticity of the component bolted (washers, nuts, and in this case fork crown and the threads inside the brake caliper) So a rigid, hard bolt will crush these components past their yielding or breaking point before anti-loosing function is achieved, an elastic washer (Grover) will not work because the amount of force is very low for a spring (suitable for a 4-6grade) this is the reason you don't find Grover washers on a bike (because a bike uses mostly 8.8 bolts which are suitable for a solid steel washer, and 10.9 bolts require hardned hashers of higher grade, and most 12.9 bolt require no wasers but the components assembled must be super resilient to withstand such force but brake mounts/seat-belt mounts/roll-cage mounts in a car comply to this. (Most modern cars have reinforced A and B pillar wit ultra high strength steeel that withstand strss up to 2100MPa)


Now for this problem: see how bent is the bolt, if it's cracked or anything, and leave it like that if it's bent or get a replacement bolt or replace the whole caliper. First of all see if the fork suffered any damage.
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Old 06-12-10, 05:37 PM   #10
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I would like to see the pics of the fork and front wheel. I can't really understand how your car only hit the brake caliper (assemebly) and bent it. It sounds to me like this is better left to the shop to correct. unless you have a buddy who does his own work and look at it.

I hope the fork and frame are OK that looks like a nice Bianchi
+1 Its other damage that would worry me. A new bolt, or at worst, a replacement caliper, and that brake will be fine. But how do you twist/mangle a brake caliper and not do other damage?
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Old 06-12-10, 06:13 PM   #11
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Originally Posted by Asi;10953465[...
A medium bolt 8.8 is more elastic and require less force to be installed correctly, and at this less force everything holds up.

I'm not going to spend a lot of time on this -- just enough to note that Young's modulus is approximately the same for an alloy independent of it's yield strength. A stronger bolt of the same size and material will stretch pretty much the same a bolt of lesser strength.
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Old 06-12-10, 06:57 PM   #12
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Only in Bicycle Mechanics will you have a bunch of nuts debating the sanity of straightening the mounting post of a sidepull brake caliper.

Hell, even the C&V Campyphiles would just replace the post with another one.

-Kurt
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Old 06-12-10, 08:31 PM   #13
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Only in Bicycle Mechanics will you have a bunch of nuts debating the sanity of straightening the mounting post of a sidepull brake caliper.

Hell, even the C&V Campyphiles would just replace the post with another one.

-Kurt
Pun intended? Nuts debating bolts?
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Old 06-12-10, 08:32 PM   #14
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Only in Bicycle Mechanics will you have a bunch of nuts debating the sanity of straightening the mounting post of a sidepull brake caliper.

Hell, even the C&V Campyphiles would just replace the post with another one.

-Kurt
Pun intended? Nuts debating bolts?
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Old 06-12-10, 08:49 PM   #15
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Only in Bicycle Mechanics will you have a bunch of nuts debating the sanity of straightening the mounting post of a sidepull brake caliper.

Hell, even the C&V Campyphiles would just replace the post with another one.

-Kurt
on those Modolos? I would opt new brakes instead
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Old 06-12-10, 09:09 PM   #16
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on those Modolos? I would opt new brakes instead

+1. Unless it's a rare, collector-grade bike, replacing the damaged caliper with an inexpensive dual-pivot caliper will result in better braking, easier adjustment, restored hair growth, and improved performance in bed. Trust me, I'm a scientist.
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Old 06-12-10, 11:00 PM   #17
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+1. Unless it's a rare, collector-grade bike, replacing the damaged caliper with an inexpensive dual-pivot caliper will result in better braking, easier adjustment, restored hair growth, and improved performance in bed. Trust me, I'm a scientist.
Dual-pivot, or simply putting another classic single-pivot on it (Modolo, Mafac LS, Campag NR/SR/Triomphe/Victory/Nuovo G.S., et. cetera), if the rider prefers the stiff-spring Campag NR feel.

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Old 06-13-10, 06:44 AM   #18
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I'm not going to spend a lot of time on this -- just enough to note that Young's modulus is approximately the same for an alloy independent of it's yield strength. A stronger bolt of the same size and material will stretch pretty much the same a bolt of lesser strength.
+1.
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Old 06-20-10, 12:28 AM   #19
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I would like to see the pics of the fork and front wheel. I can't really understand how your car only hit the brake caliper (assemebly) and bent it. It sounds to me like this is better left to the shop to correct. unless you have a buddy who does his own work and look at it.

I hope the fork and frame are OK that looks like a nice Bianchi
I actually haven't had the chance to take it to the shop yet, but I did remove the caliper. The fork and frame are fine. I'm pretty sure I bent the caliper, no big deal. I'll get around to getting it fixed sooner or later.

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+1 Its other damage that would worry me. A new bolt, or at worst, a replacement caliper, and that brake will be fine. But how do you twist/mangle a brake caliper and not do other damage?
Quick reflexes . My garage is really cramped and my car is really wide so it's not a good combo. My bikes just lean up against the wall on the driver side so I must have just barely hit it and not touched the frame/forks. Good news though, I'm getting pegboard installed, so within a few weeks they will be hanging from the wall, safe from the reaches of my evil Accord.

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Dual-pivot, or simply putting another classic single-pivot on it (Modolo, Mafac LS, Campag NR/SR/Triomphe/Victory/Nuovo G.S., et. cetera), if the rider prefers the stiff-spring Campag NR feel.

-Kurt
Sounds like a plan.

As for "bolt theory", well, I'll have to leave that to the people at the shop

Thanks everyone!
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Old 06-20-10, 11:09 PM   #20
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Did it hit the frame and bed that way?
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