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you assume the cost of all necessary servicing, repair, correction or
This page discusses the maintenance of coaster brake bicycles. A loss of braking power could lead to death or severe injury, especially on hills or in traffic. Your coaster brake may not match the one described in this document. This document may not clearly express the assembly of the coaster brake it describes, or may even contain errors. We are not responsible. If you use the information in this document, you take full responsibility for the outcome. If that is not acceptable to you, please do not read this document.
In all cases, I strongly recommend you install a front brake so if the back brake goes out, you can still stop. If such a front brake is installed, it must be installed in such a way that it will not fall off, which in itself could cause death or severe injury (through flipping the bike).
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If this is not acceptable to
you, you may not read this information.
You can get most of these benefits with a seven speed with coaster brakes using a Shimano Nexus multispeed hub. I now recommend using a multispeed bike as a daily driver, because doing so provides more exercise, keeping the rider in the kind of shape necessary to run twenty mile (each way) errands.
|To the left you see the wheel mounted on the outside of the fork, with the sprocket facing outward. This gives a stable working environment, and to some degree immobilizes the axle. I disassembled from the sprocket in. The next step is to remove the locknut and cone holding the sprocket on the wheel.|
|I removed the locknut by placing the adjustable wrench on the locknut and the cone wrench on the cone. The cone provides a riding surface for the bearings. Because both the cone and locknut unscrew counterclockwise, the locknut is twisted counterclockwise while the cone is held steady. The locknut and cone are first separated, and then removed.|
|Here you see the locknut is gone and the cone has been unscrewed to the end of the axle. The bearing has been removed to make it visible, and to reveal the bearing cone surface in the sprocket.|
|The next step is to remove the sprocket. Twist it counter clockwise, and it comes out. Once it's removed, you can see why twisting counter clockwise removed it. The back side of the sprocket has thick, course threads. In the picture on the left you can also see the bearing that rides between a cone on the back side of the sprocket and the cup in the hub. The sprocket and bearing can now be completely removed, but the wheel SHOULDN'T be removed at this time.|
|This is what it looks like after the wheel has been removed and the brake pads have fallen out. You now see the axle, with (toward fork) the clutch assembly, the brakepad locking assembly (barely visible though the grease), the bearing, the torque arm, the left side locknut, and the fork. For the purposes of this document, we'll consider the brakepad locking assembly, the torque arm and the left side locknut to be a unit, because I did not separate them. They have no moving parts, so separating them would have made cleaning slightly easier, but would have lost the information concerning where to lock the brake locking assembly.|
|To the left is a picture of all the parts comprising the
hub, except the wheel, which goes in the large gap in the center. The
names of the parts are listed below:
|The outside surface of the brakepads. The grooves help it grab the inside of the hub, and also shed impurities like grease.
|The inside surface of the brakepads. On one end, the ridge
interlocks with the brakepad locking assembly, preventing them from
turning with the hub and thus enabling braking. On the other end is a
slanted surface over which the clutch assembly glides, so that the
brakepads can be pushed out to rub the inside of the hub..
|Here's the brakepad locking assembly with axle and torque
arm. You can see one of the two raised parts that interlock with the
brake pads to prevent the brake pads from turning. Farther back you see
the cone surface on which ride the bearings that also ride the cup of
the hub shell. The following picture shows both raised parts:
|Here's a straight on view showing the two parts that lock with the brake pads.
|Here's a side view of the clutch assembly. On the left you
see two little pawls that lock into the brake locking assembly. They're
on a little "platform" that's connected to the main body via a spring
loaded clutch mechanism. When the main body turns clockwise with
respect to the "platform", there is a constant friction. It's that
friction that enables the rider to pedal forward and "suck" the clutch
assembly toward the sprocket assembly. Otherwise, the main body would
just rotate with the sprocket assembly and go nowhere. Once the main
body of the clutch assembly is engaged with the lip inside the hub
shell, the main body rotates while the "platform" doesn't.
The clutch mechanism does not allow the main body to rotate counterclockwise with respect to the platform. That way back peddling quickly pushes the clutch assembly away from the sprocket assembly (one wouldn't want the clutch to rotate with the sprocket, even a little, or braking would be delayed).
The spring loaded clutch assembly also allows a moderate force to push the main body toward the platform. Such compression is necessary to achieve braking. More to the point, the spring's tendency to thrust the platform and body away from each other enables the rider to switch from braking to coasting, without peddling forward.
The little pawls on the "platform" always remain inserted in the brakpad locking assembly. The left and right movement of the clutch body is achieved by compression and uncompression of the spring.
Also visible in the picture is the slanted ribbed surface in the middle of the clutch body. In braking, as the clutch body is thrust toward the platform, the brake pads ride up this slanted surface and are thrust into the interior diameter of the hub shell, initiating braking.
an interior view of the clutch assembly. I highly processed this image in Gimp
in order that you could see the threads. These threads mesh with the
external threads on the projection on the back of the sprocket assembly
so that when you pedal backwards, the clutch assembly is forced toward
the left and pushes the brake pads out and into the interior walls of
|This is the hub shell, photographed through the left (wider)
side. You can see the bearing cup around the edge -- this is where the
bearing rides. There's another one on the right side.
The important part of this photograph is the difference in diameters between the wider left side and the narrower right side. The diameter change occurs abruptly at a lip inside the hub shell. This lip can be seen upon careful examination of this photo. You might want to click the photo for a full sized version. It is this lip that the clutch main body butts up against during forward peddling. The sprocket assembly transmits power to the clutch assembly, which then transmits power to the hub shell via the contact between the clutch main body and this lip.
Note that to make the lip even somewhat visible, I had to use Gimp to lighten the interior, which is why the interior appears much lighter than the ball cup, and appears almost as bright as the flange. If you look carefully you'll also notice it has less than 36 spokes. I took this picture after my 26" wheel was already rebuilt (and had 40 miles on the rebuild), and so I took a picture of a hub off a thrift-store girl's 20 inch bike my wife bought for $7.00, for our daughter who since outgrew 20 inch bikes, leaving it available for cannibalization.
a view of the back side of the sprocket. Note the external threads,
which mesh with the internal threads of the clutch assembly. Notice
also that below (in this picture) the threads is a cone on which ball
bearings race. The ball bearings run between this cone and a cup in the
|Coaster Brake States|
|Sprocket||Force applied in wheel rotation direction, rotates in that same direction.||No force applied, no rotation.||Force applied in direction counter to wheel rotation.|
|Clutch main body||Pushed to the right until it butts up against the lip inside the hub shell. Rotates in wheel rotation direction. Obtains energy from sprocket assembly via course threads. Transmits energy to the wheel hub via the force between it and the hub shell lip.||Floats to the left of the lip, but not so far left as to push the brakepads outward.||Pushed to the left far enough to spread the brake pads.|
|Clutch platform||No rotation. No lateral movement.||No rotation. No lateral movement.||No rotation. No lateral movement.|
|Brake pads||No rotation. Not pushed outward.||No rotation. Not pushed outward.||No rotation. Pushed outward to contact hub shell, slowing or stopping hub rotation.|
|Brakepad locking assembly||No rotation. No torque.||No rotation. No torque.||No rotation. The brakepads apply a torque to the brakepad locking mechanism in the direction of wheel rotation. The brakepad locking mechanism in turn exerts an equal and opposite torque on the brakepads, enabling stopping.|
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