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#11
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Brake Trouble / Road Bike
Jobst Brandt wrote:
Unfortunately, bicycle repair shops, unaware of the cause, use hammers and punches to bend the offending spring I replied: That technique was appropriate for some older sidepulls, models dating from the early '70s and older, and was the only way to regulate the centering of the caliper. Jobst: I don't believe it was ever appropriate. The anchor bolt on those brakes could be rotated and the springs lubricated just the same as on later more expensive brakes. (I believe Jobst was referring to the center bolt, not the anchor bolt.) Tom Ace wrote: I had a Raleigh 3-speed with steel-caliper sidepull brakes. The front brake bolt had a cylindrical concave surface that mated with a convex surface on the fork. The bolt's rotation was not adjustable. If lubrication didn't fix the centering, the only other option I knew of was to bend the spring. That's correct for those brakes. Those were the bikes I grew up with in my early days of bike tinkering. This doesn't apply just to the front brake. The rear also has a cylindrical concavity that mates with the seatstay bridge. Most newer sidepulls use a separate "radiussed washer" to mate the flat back of the spring black with the fork crown or seatstay bridge. These do permit adjustment without bending the spring, though it still sometimes is accomplished with a hammer and punch. Many older sidepulls, such as the typical Weinmann/Dia Compe units, had no way to secure or rotate the spring mounting block. (This was before Campagnolo thought of putting wrench flats on the spring block, and before Weinmann thought of putting a 4 mm hex on the end of the center bolt.) When you would tighten the mounting nut on these calipers, the friction of the threads would often tend to rotate the center bolt out of position, even if you started with it centered. A hammer and punch used gently on the spring, close to the central block could rotate the centerbolt back to the correct orientation. This did not actually involve causing the spring to yield, it was just the only way to apply torque to the spring mounting block in the absence of wrench flats. For a while, special tools were available for grabbing the spring and twisting the center bolt but these were never common, and are probably extinct by now. The Park OBW-3 was one of these, but I don't think these are currently available. Sheldon "Technology Changes" Brown +-------------------------------------------------------------+ | Want of care does us more damage than want of knowledge. | | -- Benjamin Franklin | +-------------------------------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide http://captainbike.com http://sheldonbrown.com |
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#12
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Brake Trouble / Road Bike
Tom Ace writes:
Unfortunately, bicycle repair shops, unaware of the cause, use hammers and punches to bend the offending spring That technique was appropriate for some older sidepulls, models dating from the early '70s and older, and was the only way to regulate the centering of the caliper. I don't believe it was ever appropriate. The anchor bolt on those brakes could be rotated and the springs lubricated just the same as on later more expensive brakes. I had a Raleigh 3-speed with steel-caliper sidepull brakes. The front brake bolt had a cylindrical concave surface that mated with a convex surface on the fork. The bolt's rotation was not adjustable. If lubrication didn't fix the centering, the only other option I knew of was to bend the spring. I don't see why that was the only available method. How did you initially poisition the brake caliper was with pads adjacent to the rim? Why could the centerbolt not be rotated? I don't believe it was riveted or welded in place. Jobst Brandt |
#13
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Brake Trouble / Road Bike
Sheldon Brown writes:
Unfortunately, bicycle repair shops, unaware of the cause, use hammers and punches to bend the offending spring That technique was appropriate for some older sidepulls, models dating from the early '70s and older, and was the only way to regulate the centering of the caliper. I don't believe it was ever appropriate. The anchor bolt on those brakes could be rotated and the springs lubricated just the same as on later more expensive brakes. (I believe Jobst was referring to the center bolt, not the anchor bolt.) Please explain the difference between a center bolt and anchor bolt. I am referring to the bolt about which the caliper arms rotate and which attaches the spring boss against the fork crown or rear brake bridge. The ones to which I refer are interchangeable with Mafac centerpull and Campagnolo side pull brakes. I had a Raleigh 3-speed with steel-caliper sidepull brakes. The front brake bolt had a cylindrical concave surface that mated with a convex surface on the fork. The bolt's rotation was not adjustable. If lubrication didn't fix the centering, the only other option I knew of was to bend the spring. That's correct for those brakes. Those were the bikes I grew up with in my early days of bike tinkering. This doesn't apply just to the front brake. The rear also has a cylindrical concavity that mates with the seatstay bridge. What is "this" in "this doesn't apply only"? Most newer sidepulls use a separate "radiussed washer" to mate the flat back of the spring black with the fork crown or seatstay bridge. These do permit adjustment without bending the spring, though it still sometimes is accomplished with a hammer and punch. I don't understand why the center bolt could not be loosened and the return spring rotated, the same as it was on initial installation. Besides, if the brake was initially centered when new, clean and lubricated, it needed only to be restored to the clean and lubricated state to be centered. The springs did not yield in use and did not become asymmetrically loaded. Many older sidepulls, such as the typical Weinmann/Dia Compe units, had no way to secure or rotate the spring mounting block. (This was before Campagnolo thought of putting wrench flats on the spring block, and before Weinmann thought of putting a 4 mm hex on the end of the center bolt.) I disagree, having adjusted them initially and centering them by cleaning an lubrication. How else could one install a new brake if its rotational position was not adjustable? When you would tighten the mounting nut on these calipers, the friction of the threads would often tend to rotate the center bolt out of position, even if you started with it centered. That takes a little skill to retain the spring in its position while tightening the bolt. This is a common practice in machinery. A hammer and punch used gently on the spring, close to the central block could rotate the centerbolt back to the correct orientation. This did not actually involve causing the spring to yield, it was just the only way to apply torque to the spring mounting block in the absence of wrench flats. With a slightly looser center bolt this operation can be done without impact and with suitable accuracy. That is the whole point of bringing this up. I realize this does not correct the errors of history but it was this sort of "curbstone mechanics" that I found crude when I worked on my bicycle in grade school. I had seen better while repairing my mothers Model-A ford. For a while, special tools were available for grabbing the spring and twisting the center bolt but these were never common, and are probably extinct by now. The Park OBW-3 was one of these, but I don't think these are currently available. A bit of imaginative mechanics, even today, makes most of the special tools unnecessary. I had no need for a special brake adjusting tool. Jobst Brandt |
#14
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Brake Trouble / Road Bike
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#15
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Brake Trouble / Road Bike
wrote:
I don't see why that was the only available method. How did you initially poisition the brake caliper was with pads adjacent to the rim? Why could the centerbolt not be rotated? See http://www.yellowjersey.org/ralbrake.html You can see several parts with the cylindrical concave surface I described, which mates with the fork (or as Sheldon pointed out for the rear brake, the brake bridge) in one rotational position only. If you look closely at those pieces, you can see a groove (in the opposite flat surface, not in the concave side) that holds the spring. I don't know whether that piece is integral to the bolt, but that's not the point. What matters is that the spring is held by a piece whose rotation isn't adjustable. Tom Ace |
#16
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Brake Trouble / Road Bike
Tom Ace writes:
I don't see why that was the only available method. How did you initially position the brake caliper was with pads adjacent to the rim? Why could the center bolt not be rotated? See http://www.yellowjersey.org/ralbrake.html You can see several parts with the cylindrical concave surface I described, which mates with the fork (or as Sheldon pointed out for the rear brake, the brake bridge) in one rotational position only. If you look closely at those pieces, you can see a groove (in the opposite flat surface, not in the concave side) that holds the spring. I don't know whether that piece is integral to the bolt, but that's not the point. What matters is that the spring is held by a piece whose rotation isn't adjustable. The piece is not integral with the bolt but it is registered on the curve of the fork crown and on the diameter of some rear brake bridges. As you see in the URL cited, the springs are symmetrical as are the curves in the spring boss and these align centered on the wheel if it isn't in askew. The point is that these brakes don't even allow misadjustment when friction draws the brake off center and cleaning and lubricating is required. To hammer on the return spring only shifts the problem to a slightly later time when the friction in the spring contact point changes again. The hammer may be a quick fix, but understanding the problem and responding to it in kind is a better solution. Jobst Brandt |
#17
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Brake Trouble / Road Bike
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#18
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Brake Trouble / Road Bike
Tom Ace writes:
The hammer may be a quick fix, but understanding the problem and responding to it in kind is a better solution. I got started in this thread in response to your saying there was never a need for the hammer routine with any brake. If cleaning/lubing the Raleigh brakes doesn't center them, what else is there left to do but to bend the spring? Somehow these threads drift off into unrelated topics, probably to defend a defenseless position that no one else knows the writer holds until defended here. The subject of this thread was centering a modern high quality Shimano brake, not steel caliper Raleigh brakes of decades ago. Even those brakes recognized the problem and made spring bosses pressed onto knurled center bolts that were pressed in place to assist adjusting brake position. Let's leave the hammer and punch in the historic bin. There is no place for them on any recent aluminum alloy brake caliper. The radius was there to offer initial centering on similarly curved fork crowns. Unfortunately many fork crowns had a flat mounting surface, something I ran into right away in those days. Anyway, if the brake subsequently did not center, it had probably already been misshapen by hammer and punch. At that point, lubricating and cleaning has little effect. This was a self perpetuating routine. Jobst Brandt |
#19
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Brake Trouble / Road Bike
Quoth Jobst Brandt:
Unfortunately, bicycle repair shops, unaware of the cause, use hammers and punches to bend the offending spring I plied again: That technique was appropriate for some older sidepulls, models dating from the early '70s and older, and was the only way to regulate the centering of the caliper. Jobst: I don't believe it was ever appropriate. The anchor bolt on those brakes could be rotated and the springs lubricated just the same as on later more expensive brakes. Tom Ace took the words right out of my mouth: I had a Raleigh 3-speed with steel-caliper sidepull brakes. The front brake bolt had a cylindrical concave surface that mated with a convex surface on the fork. The bolt's rotation was not adjustable. If lubrication didn't fix the centering, the only other option I knew of was to bend the spring. I don't see why that was the only available method. How did you initially poisition the brake caliper was with pads adjacent to the rim? Why could the centerbolt not be rotated? I don't believe it was riveted or welded in place. The block on the centerbolt that had the groove for the middle of the spring also had a concave groove on the other end. The front one had a large radius to match the curvature of the front of the fork crown. The rear one had a smaller radius, transversely oriented groove that fit snugly against the seatstay bridge. These parts could not be rotated because of the curved interface to the frame/fork. Bending the spring was the _only_ way to adjust the centering. Sheldon "http://sheldonbrown.com/english" Brown +----------------------------------------+ | Yes Britain set the world ablaze, | | In good King George's glorious days! | | --W.S. Gilbert | +----------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide http://captainbike.com http://sheldonbrown.com |
#20
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Brake Trouble / Road Bike
Jobst Brandt wrote:
Unfortunately, bicycle repair shops, unaware of the cause, use hammers and punches to bend the offending spring I replied: That technique was appropriate for some older sidepulls, models dating from the early '70s and older, and was the only way to regulate the centering of the caliper. Jobst: I don't believe it was ever appropriate. The anchor bolt on those brakes could be rotated and the springs lubricated just the same as on later more expensive brakes. (I believe Jobst was referring to the center bolt, not the anchor bolt.) Please explain the difference between a center bolt and anchor bolt. I am referring to the bolt about which the caliper arms rotate and which attaches the spring boss against the fork crown or rear brake bridge. That is the "center bolt." In the industry, the term "anchor bolt" generally refers to the bolt that secures the plain end of a brake or shift cable to the caliper/cantilever or derailer. See: http://sheldonbrown.com/gloss_an-z.html#anchor The ones to which I refer are interchangeable with Mafac centerpull and Campagnolo side pull brakes. Those are not interchangeable. Mafac and other centerpulls use a semi-standard M6 bolt, though usually with a "low profile" head to improve arm clearance. Campagnolo and most other single-pivot sidepulls use a double-ended center bolt. It has a "block" in the middle with a groove that secures the spring, and has male threads protruding from both ends. One of the male threads attaches it to the frame/fork. The other male thread holds the arms and associated washers in place, using an acorn nut and a jam nut. Shimano and some other single-pivot brakes use a bolt with a head on one end, but a dual thread. There's a 7 mm thread that screws into the spring block and an associated jam nut, then it necks down to the standard 6 mm size where it fits through the frame/fork. Many older sidepulls, such as the typical Weinmann/Dia Compe units, had no way to secure or rotate the spring mounting block. (This was before Campagnolo thought of putting wrench flats on the spring block, and before Weinmann thought of putting a 4 mm hex on the end of the center bolt.) Jobst: I disagree, having adjusted them initially and centering them by cleaning an lubrication. How else could one install a new brake if its rotational position was not adjustable? When you would tighten the mounting nut on these calipers, the friction of the threads would often tend to rotate the center bolt out of position, even if you started with it centered. That takes a little skill to retain the spring in its position while tightening the bolt. This is a common practice in machinery. But the spring is a _spring_! If you hold the brake by one or both of the caliper arms, the spring deflects due to torque on the center bolt, and the spring block gets misaligned. A hammer and punch used gently on the spring, close to the central block could rotate the centerbolt back to the correct orientation. This did not actually involve causing the spring to yield, it was just the only way to apply torque to the spring mounting block in the absence of wrench flats. With a slightly looser center bolt this operation can be done without impact and with suitable accuracy. I prefer to get the center bolt tightened securely. Sheldon "It Takes All Kinds" Brown +----------------------------------------+ | All theory, dear friend, is grey, | | but the golden tree of actual life | | springs ever green. --Goethe | +----------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide http://captainbike.com http://sheldonbrown.com |
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