Figure 1 - A typical coaster hub wheel

A coaster hub is a single speed bicycle hub that allows the pilot to apply brakes by pedaling in reverse. This elegant simplicity makes the coaster hub great for non-racing type bicycles such as cruisers, cargo haulers and choppers. Because there are no derailleur or caliper brakes on a coaster bike, there are also no cables or levers, just a chain connecting the front and rear chain rings.

Coaster hubs can also be hacked into mid drive systems, allowing brakes on the axle of a trike or cargo vehicle by welding a sprocket to the steel shell. Coaster hubs are almost indestructible, so if you ever encounter a non-working unit, it may just need to be taken apart and re-greased. So, let's have a look inside and see how this marvel of simplicity works.

A coaster brake hub is very easy to identify since it will have only a single chain ring (sprocket) on the right and a supporting torque arm on the left. These hubs are found on the smallest of kids’ bikes right up to full sized beach cruisers and cargo bikes. Coaster hubs lack the ability to have more than one speed, but they do offer reliable braking and simplicity.

Figure 1 shows a typical coaster brake hub on a discarded 16 inch kids’ bike wheel. Besides the number of spoke holes, most coaster hubs are of similar quality and functionality. Made of all steel, new spoke holes are easily drilled, and other parts can be welded to the hub shell to make unique transmission systems for your own projects.

Figure 2 - A homebrew spoke screwdriver

Any suitable flathead screwdriver can be used to remove the spokes if you plan to extract the coaster hub. To make your job easier, grind a small groove out of the center of a screwdriver as shown in Figure 2. It will now be a spoke removing screwdriver that can lock into place when the spoke extends past the spoke head. If you do not care to salvage the spokes or rim, just use a grinder and zip disc to rip through the spokes rather than spend all the time to remove them individually. Large wire cutters can also slice through spokes.

Figure 3 - Removing spokes in sequence

If you plan to salvage the rim, spokes need to be removed a little bit at a time or you will bend the rim. Turn each spoke no more than one turn in the counter clockwise direction as shown in Figure 3, working around the rim from the valve hole. If you try to fully remove one spoke at a time, the tension will warp the rim after two or three spokes, and the damage may be permanent.

Figure 4 - Checking spoke tension

Once you have turned each spoke a few turns, the tension will be greatly reduced so that you can flex the spokes by hand as shown in Figure 4. At this point, the spoke heads can all be safely removed without damage to the rim.

Figure 5 - Removing the spoke heads by hand

Once the spokes are loosened enough to reduce the friction between the rim and spoke head, you can quickly turn the heads using your fingers as shown in Figure 5. If your spokes are rusty to the point of not being able to remove the heads by hand, then they are shot. Cheap spokes are not made from stainless steel and will rust. Do not try to reuse rusted or damaged spokes.

Figure 6 - All spokes removed

After all of the spoke heads are removed, the entire hub and spokes will drop from the rim as shown in Figure 6. You should be able to pull all of the spokes away from the hub now, but if you find the sprocket is getting in the way of removing the spokes, remove it as shown in Figure 8.

Figure 7 - The coaster hub removed

If spokes are in decent condition, put the heads back on, tie them together and then label them as per the diameter of the rim they were from. Decent stainless steel spokes will clean up like new with a bit of steel wool, so they are easy to recycle and reuse on other projects.

Figure 8 - Removing the snap ring

The coaster hub sprocket is held in place by a retaining ring (snap ring), which is easily removed by sliding a screwdriver under the open end to pry it from the groove. Once you have the snap ring lifted at one end as shown in Figure 8, it will pop right off along with the sprocket.

Figure 9 - The sprocket and dirt guard

The sprocket is only held on by the snap ring, but power is transferred through the three or four inner teeth into the hubs driver unit. All freehub sprockets are interchangeable, so you can alter the gear ratios by swapping them out with sprockets of varying tooth counts. Fewer teeth on the hub sprocket will mean more speed, but less climbing ability. Most coaster hub sprockets will have between 14 and 18 teeth.

Figure 10 - Removing the outer bearing

The outer axle bearings can be removed once you loosen the axle nuts as shown in Figure 10. It is easier to grip the torque arm in a vice or by hand and then remove the right side axle nuts first, as this will give you leverage. There will be a thin locking nut over the bearing race (cone nut) as shown in Figure 10.

Notice the orientation of the bearing (balls first) into the driver. Some hubs will simply have loose balls, so be careful when yanking apart a hub on your workbench! Also, there will be a huge greasy mess when digging into a coaster hub, but I have already pulled this one apart to clean all of the grease for better photos.

Figure 11 - The driver and inner bearing

The driver is responsible for activating the clutch and brake pads as well as transferring energy from the sprocket. This is the largest piece of the hub and is shown along with the inner bearing in Figure 11. Once the cone nut is removed from the axle, the driver will just fall right out of the hub, along with a huge wad of grease.

Figure 12 - Parts that form the clutch

Digging further into the coaster hub, you will find two brake pads and the clutch unit, which is the cylindrical part that the threaded end of the driver mates with. When you pedal forward, the clutch grips the hub shell, transferring energy from the sprocket into the wheel, and when you pedal in reverse, the driver pushes the clutch away, forcing it to spread the brake pads against the inside of the hub shell, creating friction which is transferred back to the torque arm. For this reason, the torque arm must be secured to the frame or the axle will simply turn under the extreme forced delivered during braking.

Figure 13 - Clutch and brake pads

There is one more axle bearing on the torque arm side of the hub as shown in Figure 13. Also shown in Figure 13 are the two braking pads, as well as the clutch unit which is pulled or pushed, depending on the rotation of the driver. If a coaster hub has failing brakes, the culprit is likely a lack of grease or dirty grease, as the pads will likely not wear out unless the hub has seen many long years of hard service.

Figure 14 - Coaster hub disassembled

Figure 14 shows the entire coaster hub assembly after removing all parts and cleaning away the grease. Once you understand the basic operation, it is very easy to put one back together (and it helps that it will only go back together one way). For fun, pull one apart and hand it to your mechanical wiz buddy and tell him or her to make it work again!

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