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COASTER BREAK REPAIR PAGE

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Preparation

Here are all the things I needed. I made sure they were available before I started:

  • For cleaning

    • 1 full can of engine cleaner

    • 1 bottle of "orange" cleaner or other water based grease cutter (not dishwashing liquid)

    • 1 small shallow pan for parts soaking

    • 1 large bucket for parts rinsing

    • Old toothbrush

    • Lots of rags

  • For working

    • Table

    • Flashlight

    • Hand cleaner

  • Tools for hub disassembly

    • One 6" adjustable wrench

    • One cone wrench combo, 13mm thru 16mm

    • One moderate sized flathead screwdriver

  • Tools for auxilliary jobs

    • Needlenose for chain

    • Chain tool for chain

    • Spoke wrench for spokes

A few comments. Be SURE you have a full can of engine cleaner. You might not use the whole thing, but you might. You'll for sure use a lot.

Theoretically you can make due with the engine cleaner alone and not use the "orange" cleaner. I found that my "orange" cleaner got some dirt left behind by the engine cleaner. Also, it's hard to get engine cleaner out of the can in sufficient quantities to really soak the parts. I used "orange" cleaner -- one could use any water based cleaner that really cuts grease, as long as it doesn't have grit. Hand cleaner is NOT ACCEPTABLE -- the grit in it will destroy bearings and bearing surfaces if even one piece of grit remains.

I got by without the needlenose -- using a screwdriver to disassemble the chain's master link, but it would have been easier with a needlenose.

Preliminary Evaluation

Before beginning work, evaluate the wheel as a whole. Is it missing a lot of spokes? Are a lot of spokes bent but not yet broken? Are parts of the rim flared or dented? Is the rim extremely out of true, to the point where straightening it would cause undue tension on some spokes and looseness on others? Are the teeth of the sprocket so chainworn that it detracts from your speed or causes the chain to jump?

Remember that a brand new 26" rear wheel with coaster brake costs somewhere between $30.00 and $50.00, depending on where you get it. Ask your local bike shop to see one. My alloy rimmed coaster brake rear wheel has a part number of 65312. I think that's a J & B Importers part number.

With the markup bike shops get on spokes and other parts, if your wheel has serious defects, trying to repair the wheel might waste time and save little money.

Dissassembly

The main challenge in dissassembly is remembering how it came apart so it can be put together in the same way. Also, at some point the brake pads will fall out. The hot tip is to remove the wheel slowly so you can see how they fit in.

In my opinion the easiest way to start is to bolt the left side of the wheel to the outside of the right rear fork.
 

 

       

 

 

 

 

 

 

 

 

 

 

 

 

      

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

       

 

 

 

 

 

 

 

 

 

 

 

 

WARNING!!! When the wheel is removed, the brake pads will fall out. Once they fall out, it's difficult to figure out where they were placed, and their orientation. Therefore, the wheel should be removed VERY slowly while looking at the side of the hub closest to the fork. If removed slowly enough, the brake pads should be visible in their original configuration, before they fall. By placing one's hand below the brake pads, the brake pads' original orientation can be preserved, to some extent, when they fall out.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

     

 

 

 

 

 

 

 

       

 

 

 

 

 


The picture above shows  all the parts except the wheel hub. Several parts will later be shown individually for a closer look. For the time being, in the preceding picture, the parts are, from left to right:

  • The left wheel nut.

  • The brakepad locking assembly, which remains on the axel. To the left of the brakepad locking assembly is the tork arm and the locknut.

  • The left bearing, which rides between the cone on the brakepad locking assembly and the cup on the wheel's hub.

  • The brakepads and the clutch assembly. The clutch assemblyh is the part between the two brake pads.

  • The wheel hub (not shown, but there's a large space where it should be.

  • The right bearing, which rides between the cup on the hub and the cone on the sprocket assembly.

  • The sproket assembly.

  • The outside bearing, which rides between the cup in the sprocket assembly and the cone.

  • The cone.

  • The locknut for the cone.

  • The right wheel nut.

 

How it works (quickstart)

The first thing to understand is that the course threads on the back side of the sprocket assembly thread into the course threads inside the clutch assembly. When you pedal forward, the threads pull the clutch assembly toward the sprocket assembly until the clutch assembly butts up against the lip inside the hub shell and transmits power to the hub shell.

When you pedal backwards, the clutch assembly is pushed away from the sprocket assembly. The brake pads are pushed up the slanted surface of the clutch assembly, causing them to rub on the interior of the hub. Because the brake pads are locked by the brakepad locking assembly, which is in turn anchored to the torque arm which is in turn screwed onto a fork stay, the brake pads cannot rotate, hence they stop the rotating hub as they press against it.

The brakepad locking assembly serves to prevent the brakepads from rotating along with the wheel when you put on the brakes. The outer right cone prevents the sproket from coming out when you put on the brakes, so instead the clutch assembly is forced in.

 

Detailed pictures

Here are some detailed pictures of some of the parts.

 

 

 

 

 

 

 

 

 

 

       

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

    

 

 

 

 

 

 

 

 

 

 

 

 

 

       

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

     

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

     

 

 

       

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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.

 

 

 

 

 

 

 

 

 

 

 

 

 

     

 

Steps for Reassembly:

  • Lightly grease all the exposed threads on the axle. This helps in all reassembly.

  • Moderately grease up the cone on the brakepad locking assembly, avoiding getting grease on other parts of the assembly.

  • Completely inundate one of the large bearing assemblies with grease, placing it on the brakepad locking assembly's cone with the ball side facing away from the torque arm and the holder side facing toward the torque arm.

  • Grease the threads inside the clutch assembly with a moderate amount of grease.

  • Slide the clutch onto the axle with the two little prongs toward the brakepad locking assembly.

  • Push lightly and rotate clutch until the two little prongs go into the two mating holes on the brakepad locking assembly.

  • Put a light to moderate amount of grease on the brakepad locking assembly and the exterior of the clutch.

  • Cover the outside of the brakepads with a VERY light coat of grease -- just enough so that metal on metal contact won't cut up the metal surfaces.

  • Fit the brakepads over the brakepad locking assembly and clutch so that the heavy metal on the interior of the brakepads fit between the raised metal on the brakepad locking assembly. This configuration keeps the brakepads from spinning while braking.

  • Very slowly, gently and carefully fit everything into the wider end of the hub. After it goes in, gently push and rotate until the bearing completely seats and bearing cannot be seen. If it doesn't go in right, or parts appear to become dislodged, remove, reseat the brakepads, and try again.

  • Put the wheel down on the axle so that the wheel is kept in place by gravity. Put the axle on a soft surface so the threads aren't damaged.

  • Put moderate grease on the cone at the back of the sprocket and the cup on the front side of the sprocket. Put moderate grease in the course threads on the projection at the back of the sprocket.

  • Heavily grease the second large bearing assembly and put it on the cup part of the sprocket assembly so that the balls face away from the sprocket and the holder side faces toward the sprocket. The idea is for the full balls to run on the cup in the hub.

  • Holding the tork arm so the guts don't fall out of the hub, push the sproket assembly, projection first, over the axle and into the hub. When it meets resistance, turn it clockwise and it will go in further. When it goes as far as it can, once again put the wheel down so that the torque arm side of the axel rests on a soft surface, keeping the wheel snugly over the clutch, brakpads and brakepad locking assembly.

  • Heavily grease the small bearing assembly, and place the balls side into the cup in the center of the sprocket assembly.

  • Moderately grease the cone, and screw it down into the ball bearing assembly to the point where there's no axle play.

  • Screw on the cone's locknut, hand tightening it onto the cone.

  • Place a cone wrench on the cone, and an adjustable wrench on the locknut, and tighten the two against each other.

  • Test for play. There should be just the tiniest amount of play, like maybe a half a millimeter at axle's end. As with all cup and cone bearing arrangements, one walks a tightrope between tightening it to binding and loosening it so there's too much play to true the wheel.

  • If there's too much play, or serious wheel binding, loosen the locknut away from the cone, readjust, and retighten. Do this until there's the right amount of play (almost none).

  • You're done with the hub rebuild.

 

 

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.

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. 

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.

Here's 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 the hub.

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.

Here's 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 hub wall.

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