BICYCLE FREEWHEEL BASICS TUTORIAL
Figure 1 - Some tools you will need
Practically every bike, trike or quad you will make will require some kind of freewheel in the transmission system. A freewheel is basically a sprocket attached to a ratchet, allowing the transmission to drive the wheel in only one direction - much like a socket wrench. Without a freewheel on a bicycle, you would have to pedal at all times, never able to coast. This type of drive system is called a "fixed drive" or "fixie", and is often used for strength training on an upright bicycle, where the rider works against the forward momentum in an attempt to slow or stop the vehicle. A similar fixed drive system would be found on a unicycle.
Removal or repair of a freewheel requires only a few basic tools as shown in Figure 1. You will need two wrenches to remove the axle nuts, and the home made Shimano style freehub removal tool, which we will discuss soon. A center punch will also be needed if you plan to take the freehub apart to re-grease the bearings or repair the ratchet system. Cone wrenches and professional freehub removal tools are also available at many bike shops, but I can tell you from experience that the simple home brew freehub remover is much better than the professional tool and will last forever. I have broken two store bought freehub tools, but have never had any problems with the home made remover.
Figure 2 - Cartridge freewheel (left) and Shimano type (right)
Before going any further, make note that there are two distinct types of multi-speed freewheels and hubs; the cartridge type as shown in the left of Figure 2 and the classic Shimano type shown on the right of Figure 2. Only the Shimano type of freehub can be used for trike or quad axle mounting as it can be removed as a complete working unit by unthreading it from the hub as will be shown soon. The cartridge style freewheel cannot be removed from the hub (only the chain rings), as the ratchet system is built into the hub as an integral unit.
A Shimano freewheel is easily identifiable as it will have a recessed bearing race with two or more small holes in the ring that allow it to be removed. The cartridge steel freewheel will not have a visible bearing race, but instead a spline with several inner teeth. Cartridge style freewheels are usually found on more expensive wheels and aluminum hubs, whereas the Shimano style is usually used on lower quality department store bicycles, often having a steel hub.
Figure 3 - Removing the wheel axle
Before you can remove a freewheel from a hub, you must remove the axle, as it will be in the way of the inner spline that our removal tool will need to lock with. To remove the axle, place a wrench on the cone nut and another on the lock nut on the non-freehub side of the axle as shown in Figure 3. Turn the wrenches in the direction shown in Figure 3, so that the top wrench removes the lock nut in the counter clockwise direction. With the lock nut removed, the larger cone nut will easily unthread from the axle if the threads are not damaged. If the threads are in rough shape, you may need to grip the freewheel side of the axle while removing the nuts.
Figure 4 - The hub bearings
Depending on the manufacturer of your hub, the bearings may fall out individually or be held together by a small retainer ring. As shown in Figure 4, the bearings in the hub were individual and because the grease was minimal, they simply fell out. Keep this in mind if you plan to reassemble the hub, and carefully remove the last nut so you can catch the bearings because they may fall right out. A bucket over the hub does a nice job.
Figure 5 - The hub axle hardware
The complete axle assembly is shown in Figure 5 after removal of the left side nuts and all of the bearings. The hardware on both sides of an axle are the same, but the spacer on the freewheel side is much longer in order to allow the lock nut to clear the inside of the freewheel. This is necessary because the lock nut must press against the inside of the rear dropouts when mounting a rear wheel to a frame.
Figure 6 - The inside spline on a Shimano freewheel
Figure 6 shown the internal spline on the Shimano style freehub, which is where your removal tool must lock in order to unthread the freewheel from the threaded hub body. You can purchase a tool from many bike shops that will mate with this spline, allowing you to adapt a wrench, but be warned - these tools are easy to strip, and often fail to remove an old freewheel that has been torqued on from years of use. The home built tool shown next is much better.
Figure 7 - Find a bolt that is slightly too large
To create your own hub busting tool, start by finding a bolt that is slightly too large to fit into the freewheel spline. The tips of the bolt head should sit over the spline as shown in Figure 7. The bolt I found that worked well was about 7/8" across from one flat side to the other as shown in Figure 7.
Figure 8 - Making the bolt fit into the spline
The freehub removal tool is ultra simple; a bolt ground to fit into the spline and then welded to a lever with a length of at least 12 inches. As you can see in Figure 8, a little work with the angle grinder on the edges of the bolt will make it fit snugly into the freewheel spline. It should be easy to press into the spline, but not so tight that you need to hammer it in. Just work at the bolt with your grinder a bit at a time until it fits as shown in Figure 8.
The bolt is then welded to some type of steel rod or arm so that it can be used like a long wrench to muscle off the threaded freewheel from the hub. I used a retro crank arm from my scrap pile, as it was easy to weld the bolt into the axle hole. The arm was the perfect length to allow good mechanical advantage.
Figure 9 - Using the freewheel removal tool
To use the freewheel removal tool, press the bolt head into the spline and then crank on the arm in the counter clockwise rotation as shown in Figure 9. This process requires that the wheel still be laced to the hub or you will not have any way to hold it in place as you crank on the removal tool. Also, I can almost guarantee you that banging the tool with a hammer will be the only way to free a well used freewheel from the hub threads, so cranking it by hand may be futile. Once you get the freewheel to start turning, it will easily unscrew from the hub.
Figure 10 - The threaded hub
The threaded hub body is shown in Figure 10 after unscrewing the freewheel using the home built removal tool. These threads are 1.375 inch by 24 TPI for a distance of about 3/8 inch along the hub body. These threads are the same for multi speed hubs as well as single speed BMX style hubs. The hub body shown in Figure 10 is the cheap steel type, which is great for using in your own projects as it can be cut and welded with ease.
Figure 11- A typical Shimano freewheel
The typical Shimano freehub is shown in Figure 11 after removal from the threaded hub body. This unit has 6 chain rings, and they are often available with as few as five rings and as many as nine rings. The ratchet system is built into the body of the freehub, so this unit can easily be adapted to any hub or axle with the required threads.
Figure 12 - The threaded body of the ratchet system
The threaded part on the underside of the freehub (shown in Figure 12) is actually the built in ratchet system, allowing the chain ring to turn freely in the counter clockwise rotation and lock to the hub in the clockwise rotation. Because the inside diameter of the splined area is greater than 3/4 inch, it is easy to adapt these freewheels to a variety of axles for trike or quad usage. A cartridge freehub cannot be adapted to an axle.
Figure 13 - Removing a BMX freewheel
Although a BMX (single speed) freewheel has the same type of threaded mounting system, it cannot be removed by the home built removal tool because there is no internal spline. A BMX freewheel will often only have two small holes on the face, so you will need a center punch to tap off the freewheel.
Place a punch in one of the holes and tap it so the freewheel can be unscrewed in the counter clockwise rotation. It will take awhile to remove the freewheel using this method, and many small taps should be used rather than powerful hits or you may damage the hard surface or break your punch. Switch between the holes often while removing the freehub.
Figure 14 - Two types of threaded freewheels
Figure 14 shows both the multi-speed freewheel as well as the single speed BMX freewheel after removal from the hub. Besides having only a single chain ring, the BMX freewheel also requires a larger width chain than the multi-speed freehub. Other than that, the ratcheting operation is identical.
Figure 15 - Removal of the top bearing race
Chances are you will never have any need to take a freewheel apart, but I am going to rip one open so you can see what makes it tick. Because all of the parts inside are made from extremely hard steel, there is not much room for modification or welding, so hacking a freehub into something new is probably not a good idea.
Freewheels contain many tiny free floating bearings on the top and bottom, so you will need a bucket or cloth under the freewheel when you are taking one apart as the bearings are only slightly greased (if at all), and will fall all over the place. As shown in Figure 15, the top bearing race is tapped off in the clockwise rotation by using a center punch in one of the small holes on the face. Tap lightly, switching holes as you work so you do not damage the hard steel ring.
Figure 17 - All of the internal ratchet parts
Once you remove all of the internal ratchet parts and clean the loose bearings, you will have what is shown in Figure 17. The two small bits that were held to the body with the small retaining ring are called pawls, and their job is to lock to the ratchet inside the freewheel body. It is the pawls that make the clicking sound against the ratchet teeth when you spin your freewheel in reverse.
Figure 19 - Putting the freewheel back together
To reassemble the freewheel, you will have to place all of the bearings back on the top and bottom just as they were before they fell out all over your garage floor. To make this job easy, find some grease and collect all of the bearings so you can place them back into position. The grease will be used to stick the bearings in place while you put the freewheel back together.
Figure 20 - Bottom bearings installed
By using your finger to run a small bead of grease around the bearing race, it's easier to then drop the bearings in place as shown in Figure 20, sticking them to the grease. Once you have an entire ring of bearings stuck in place on the lower race, drop the ratchet body (with pawls installed) back where it came from as shown in Figure 20.
Figure 21 - Top bearings installed
Installation of the top ring of bearings is the same - add the grease, then place them in one at a time until they stick into position. If you seem to be two or three bearings short on the top, don't worry, this is actually how the manufacturer built the freewheel, often with a gap of two or more missing bearings on the top. There is almost zero force on these bearings since they are only in use when the wheel is coasting, so a few missing bearings is unimportant. Also, remember that that top race has reversed threads, so it will screw back on in the counter clockwise rotation.
Figure 22 - A threaded freewheel on a trike
Because these Shimano type freewheels are a complete working unit, they can easily be adapted to a trike axle using a threaded part like the one shown in Figure 22. Almost all of the trike or quads on this site use this type of mounting system because it is inexpensive and extremely robust. On this particular trike, a disc brake adapter has also been added to the freewheel adapter.
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