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Older multi-speed bicycles have simple rear hubs with a set of threads on the right side of the hub shell. A traditional freewheel cluster has matching threads which screw onto the hub.
This is different from the more modern "Freehub ®" or "cassette hub" design, in which the freewheeling ratchet mechanism is a more-or-less integral part of the hub. See also my article on Cassette Hubs.
A standard freewheel attaches to a hub by screwing on to external threads that are part of the hub. Pedaling tightens the freewheel down on the threads, so no tools are required to install a freewheel.
|Italian||1.378" x 24 tpi||35 x 1.058 mm|
|ISO||1.375" x 24 tpi||34.92 x 1.058 mm|
|British||1.370" x 24 tpi||34.80 x 1.058 mm|
|French||1.366" x 25.4 tpi||34.7 x 1 mm|
|Metric BMX||1.181" x 25.4 tpi||30 x 1 mm|
All recent freewheels and threaded hubs, regardless of where made, use ISO threading. The older British and Italian standards use the same thread pitch but a very slightly different thread diameter, and are generally interchangeable. However, for strong riders and on tandems, it is best not to mix and match -- freewheels sometimes do strip the threads of aluminium hubs. A French freewheel may start to thread onto an ISO/British/Italian hub but will soon bind. An ISO/British/Italian freewheel will skim the top of the threads of a French hub and will slip forward if an attempt is made to use it. Do not force a freewheel -- you will ruin the hub.
A bottom-bracket cup can serve as a thread gauge for a freewheel: Dimensions are usually marked on cups. Hold the threads of the bottom-bracket cup against those of the hub, and look in between, against the light. If the threads engage tightly all the way across, the thread pitch is the same. If they rock across each other, it is different. You may check the thread pitch of a freewheel by threading an ISO left bottom-bracket cup into it (not a right cup, which is left-threaded). The cup will go in easily if the thread pitch is the same -- but do have a freewheel extractor tool handy so you can unscrew the cup.
Freewheels screw onto the hub without any tools, then, as you ride the bike, your pedaling effort tightens them down.
A freewheel that has been ridden for a long time, especially by a strong rider with low gears, may be quite difficult to remove because the threads are so tight.
Freewheel bodies have a larger diameter than the spoking flange of many hubs. Warning: loosen a freewheel before cutting the spokes to replace the rim, otherwise you may not be able to loosen the freewheel or to replace the spokes on the right side of the wheel. The barrel (between the flanges) of many hubs will break if you respoke only the left side and then try to unscrew the freewheel.
Although you can screw the freewheel on by hand, just by turning the sprockets clockwise, when you want to remove it, the sprockets don't help, because the freewheel's ratchet mechanism lets it spin freely counterclockwise. To remove a freewheel requires a special tool, commonly called a "freewheel puller" or "freewheel extractor", to grab hold of the core of the freewheel.
This tool is a splined unit that may be mounted in a vise or turned with a wrench. The splines engage matching splines in the interior (non-rotating) part of the freewheel body. Different brands of freewheels have used different spline patterns, but there is a recent tendency to standardize on the Shimano pattern.
Older freewheels had simple notches and matching extractors with two or four "bosses" (prongs.) The shape and spacing of these prongs would vary from one brand to another. It was very common for the prongs to get rounded off or broken, and to ruin the freewheel. Once the notches are damaged, or to remove and discard an old freewheel for which you have no tool, you must disassemble the freewheel and clamp the core into a vise -- left side of the wheel up -- then unscrew the wheel counterclockwise.
When using a boss-type freewheel puller, the tool should be secured against the freewheel by tightening down the axle nut or quick release skewer (with the springs left off). Once the freewheel has broken loose from the hub, remove the axle nut or skewer before unscrewing the freewheel any further -- or else you will break something.
|Some Popular Freewheel Tools|
Shimano large-spline current model, 12 splines
(Also works for SRAM/Sachs and most HG cassette lock rings.)
(About the same outside diameter as a nickel.)
The usual technique for removing a freewheel from its hub is to clamp the freewheel puller into a solidly-mounted vise and unscrew the wheel from the freewheel. If your vise allows this, it works better if you clamp it so that the wheel is in a vertical position. permitting you to twist harder without having your feet slip on the floor. This gives you better purchase to turn the wheel. I used to work in a shop where we had a vise mounted sideways on a door frame for this purpose. My present vise has an extra pivot that permits the jaws to be rotated 360 degrees. Unfortunately, most vises lack this useful feature, so you may have to make do with a horizontal wheel orientation.
An alternate approach which I have found to work quite well for really obstinate freewheels is to use a suitable box wrench to hold the tool, and strike the wrench handle sharply with a big rubber mallet. I use a Park chain whip, because it has a hexagonal hole in the handle that fits Park freewheel pullers perfectly.
Installing a freewheel is quite easy, and requires no tools at all. Basically you just screw the freewheel on as you would screw the cap onto a jar. The final tightening will occur by "foot power" as soon as you ride up your first hill. You can feel the freewheel slip forward. Still, if you are building up a bicycle for someone else, it's a good idea to tighten the sprockets with a chain tool, or to pedal the bicycle in all the threaded sprockets, to avoid creating the impression that something is wrong.
The foot power is very considerable, and that's why it can be so hard to remove a freewheel that has been used for a while, especially on a bike with low gearing. To prevent future difficulty with removal, it is very important to grease the threads before screwing a freewheel onto your hub!
The type of grease used is not all that important, but you must use something. The anti-seize compound that is commonly used for spoke nipples also works.
Make very sure that the freewheel is going on straight. Freewheel threads are unusually fine for their diameter, and the aluminium threads on the hub are soft, easily damaged if you cross-thread the freewheel. Again, if the freewheel is going on straight but starts to bind, don't force it: you have mismatched threads and will damage the hub.
Freewheels should be oiled from time to time with a medium-weight oil. This is easy to do, and generally requires no disassembly.
The bike should be held with the rear wheel off the ground, and leaning to the left at about a 45 degree angle. An assistant may be helpful for this. Turn the pedals around a couple of times to get the wheel spinning fast, then let it coast (helps to be in high gear for this.)
Look inside the smallest sprocket. The sprocket will be stationary, since the wheel is coasting, but you'll see an inner part of the freewheel that is spinning with the wheel. Drip oil onto the crack between the turning part and the stationary part. Gravity and capillary action will help work oil into the freewheel.
Repeat this a few times, until you hear a change in the sound of the clicking pawls (they'll generally get quieter when the oil reaches them.)
Most multi-speed freewheels have replaceable, interchangeable sprockets. It used to be a common bike-shop service to assemble custom freewheels with any desired combination of sprocket sizes. Unfortunately, with the general decline in freewheels, replacement sprockets are no longer as readily available as they once were. They do show up on eBay, and it is also possible to restore an older, worn sprocket with some judicious grinding.
Sprockets of older freewheels had taller teeth than are usual today. When a sprocket and chain wore together, they would form a hook shape at the back side of each sprocket tooth. A new, replacement chain's shorter links would fall into the hollow behind the hook of one tooth, ride up over the next tooth, and jump forward when that tooth came around to the top.
It is possible to extend the life of a hooked sprocket by grinding off the hooks with a Dremel tool or disk sander. The hardened metal surface has already worn off, so the revived sprocket will wear faster than a new one. Newer sprockets must usually simply be replaced, as the teeth are not tall enough to allow of restoration: see my article on sprocket and chain wear.
To remove sprockets from a freewheel for replacement or restoration, you normally use two chain whips: one to unscrew the sprocket, the other to prevent the freewheel from rotating backwards. This is easiest with the freewheel installed on the wheel. Or you can use a special freewheel vise in place of the second chain whip. Remove the freewheel from the wheel to use the freewheel vise.
Freewheel vise. The photo is for illustration only. The freewheel vise must be clamped in a bench vise in use and when separating two sprockets of nearly the same size, place the smaller one underneath, for less interference with the chain whip.
Older European freewheels mostly used all threaded sprockets. Usually the two largest would have left threading, and would have to be removed/replaced at the wide end of the freewheel. Because of the low gearing provided by the larger sprockets, they would usually be screwed on very, very tight, and could require a considerable amount of effort to unscrew. The smaller sprockets would screw on from the outside, using normal right threading. If you don't have a chain whip, or if you are trying to remove a particularly stubborn threaded sprocket, you can substitute a short length of chain held in a vise
A length of chain and a bench vise also can clamp a sprocket
In practice, you usually did not have to remove all of the sprockets at the same time, because you needed a sprocket to hold the freewheel in place while you unscrewed the one you wanted to remove. There were special vises that gripped the threads to let you take off the last sprocket, but I never found the need to use one. Another way to remove all of the sprockets is to tighten the two largest ones against each other, loosen the remaining smaller sprocket and then unscrew the largest sprockets from each other. British Cyclo freewheels were different -- all the sprockets screwed on from the left except the smallest -- and quickest wearing -- one! This sprocket was integral with the freewheel body and could not be removed. Mechanics who didn't know this have broken teeth off this sprocket trying to remove it. But that's ancient history and you will probably never see a British Cyclo freewheel!
Newer freewheels use splined sprockets: you need only unscrew one or two outer sprockets, and then the others slip off. Shimano Hyperglide freewheels use all splined sprockets, with a threaded lockring similar to the system used on Hyperglide cassette hubs.
Keep track of the spacers between the sprockets, to maintain correct sprocket spacing when you reassemble the freewheel. When reassembling the sprockets to the freewheel body, grease the threads to prevent corrosion and make removal easier the next time.
Many sprockets are asymmetrical. The high side of the teeth of SunTour sprockets faces to the right. The ramps for chain pickup on newer sprockets also face to the right. If installed backwards, these sprockets will shift very poorly. Some older sprockets are symmetrical, so you can extend their life by turning them over.
With older freewheels, there were commonly 2 or 3 different thread sizes on the same freewheel, so sprockets made for one position wouldn't necessarily fit on another position. Threaded sprockets also had built-in spacers, so they could only be installed in one direction.
In the mid-1970s, SunTour and later, Shimano took the freewheel business away from the long-established European manufacturers, such as Atom, Campagnolo, Cyclo, Everest, Maillard, Regina, TDC... by virtue of greatly superior design and workmanship, even though the metallurgy of the Japanese products was not as good:
|French freewheel with weak notches||SunTour freewheel with stronger notches.|
The first multiple-speed freewheels had 3 sprockets, using the traditional 1/8" chain.
Standard spaced 6-speeds required increasing the frame spacing to 126 mm, aggravating the problems introduced with the move to 5-speed, but still providing satisfactory service in most cases.
As it turned out, the increased length of unsupported axle sticking out from the right side of the hub was just too long for traditional 10 mm threaded axles. 8-speed freewheels were sold for several years, but a very large percentage of the riders who bought them wound up having problems with axle breakage/bendage. As a result, 8-speed freewheels eventually pretty much disappeared from the market.
This also coincided with the increasing popularity of the cassette Freehub ® which didn't have the problem of axle protrusion. As the number of sprockets has continued to increase to 9 and beyond, thread-on freewheels have become obsolete for high-end applications. As of 2012, SunRace makes 8-and 9-speed freewheels, but all modern derailer bikes of decent quality use the much superior cassette Freehub system.
[ Most of this section can be blamed on John Allen :-) ]
Do you need to replace an older, threaded rear hub to update to a modern, index-shifting drivetrain?
Not unless you insist on having more rear sprockets than you probably need. It's nice spec hype to advertise 9, 10, 11 speeds at the rear, but you can get a wide range and narrow steps with 6 or 7 sprockets and wide-step double (see example) or triple chainwheels.
Modern 5-and 6-speed freewheels have a 5.5 mm sprocket spacing and work with Shimano 5-and 6-speed shifters. 7-speed freewheels -- and old SunTour Ultra freewheels -- have a 5 mm sprocket-to-sprocket spacing that works with Shimano 7- or 8-speed click shifters and rear derailers -- see table of sprocket spacings. (You may need to adjust the cable routing slightly with an 8-speed shifter). An index shifter's extra clicks will be blocked by the limit stop on the derailer. 8-speed chain works with all of these freewheels, and it is more durable than the narrower chains used for 9 or more speeds.
7-speed freewheels with 13-15-17-19-21-24-28 teeth are available from Shimano, SunRace and IRD. This is a nice, even progression, or you may choose another -- see list of available freewheels from Harris Cyclery. Modern freewheels have the same easy-shifting features as cassettes.
Unless you are willing to put up with friction shifting, you need to install new shifters. Indexing handlebar-end shifters, top-mount shifters or downtube shift levers let you know how to shift by feel. Brake-lever shifters return to the same position after every shift, so you don't know what gear you are using. They also tend to be expensive. Brazed-on bosses for downtube shifters on some older frames will not fit today's index shift levers or cable stops, so you may need to use a clamp-on adapter.
A 5-speed freewheel or SunTour Ultra-6 will work with the 120 mm rear dropout spacing that was usual in the 1970s. A 7-speed freewheel needs at least 126 mm spacing, but only steel frames are likely to have narrower spacing, and they can usually be cold set to spread the dropouts. You also may need to redish the rear wheel-- see article on frame spacing. To convert to a cassette, you would have to replace the rear wheel.
To be sure, freewheel choices are somewhat limited, unless you have been hoarding old sprockets. Back in the days of 4-, 5-, even 6-speed freewheels, it used to be common to customize the ratios. When there were so few sprocket positions available, it was more important to provide the specific sizes desired to match a given rider's style and riding conditions.
As gears proliferated through 7-, 8-, 9- and now 10-speed cassettes, this became less of an issue. As a result, custom gearing is now much less common than formerly. But with a wide-range triple crankset, this is not much of an issue.
On the other hand -- many older cyclists assume that it is harder to customize cassette-type clusters than it was with the old thread-on freewheels. In fact, the opposite is the case! Cassettes are much easier to customize, because all of the sprockets use the same spline pattern, so any of the sprockets (except the smallest one) can be used at any position on the Freehub body. With thread-on freewheels, the body is "stepped" so that sprockets for different positions will attach with different spline or thread patterns. Back in the day, better bike shops would have a big "sprocket board" with dozens of hooks to stock all of the various permutations of tooth count and attachment size needed to create custom freewheels. Generally each different manufacturer would require a different sprocket board, because each manufacturer would have its own proprietary design.
Some SunTour Pro Compe and Perfect freewheels tend to unscrew the lockring. Fortunately, only the bearing balls will fall out: the axle and dropout will retain the other parts. It is usually possible to screw the lockring back in (counterclockwise) and ride home as long as you don't coast.
Some freewheels also have one more internal shim than needed, making them rock noticeably as you ride. So, you may need to service a freewheel, if you want to keep it.
Note: Except in urgent cases:
working on freewheel bodies is generally not worth the trouble. The freewheel is the least important bearing on a bicycle, since it only turns when it is not carrying any load.
Some people will ignore my advice and try to service freewheels (or have no choice), so here's how to do it.
Leave the freewheel in place on the wheel, or screw it onto a wheel, so that you will have something to hold it with. Breaking the freewheel loose from the wheel now with a freewheel remover reduces the likelihood of damage to the inner body later.
You should see a ring with two holes in it for a pin spanner to fit into. This is usually the ring which has the brand name of the freewheel marked, and may also have an arrow pointing clockwise, and the word "remove" in one language or another.
If you don't see such a ring, you may need to remove the smallest sprocket to gain access to it. This is common on freewheels with 13 tooth or smaller sprockets. You will need two chain whips, one to unscrew the smallest sprocket, another hold the freewheel so that it doesn't spin backward while you unscrew the top sprocket. You also will need about 100 1/8"bearing balls for most freewheels.
Use a hammer and punch (or an old flat-blade screwdriver) alternately in one hole, then the other, to drive the ring in a clockwise direction. This ring is actually a bearing cone with a left ("reverse") thread, and once you have removed it you will see a row of 1/8" bearing balls and a stack of very thin washers surrounding the threads that the cone threaded on to. These are shim washers, and you can remove one or more of them to make the bearing tighter, if the freewheel has too much play.
If you want to disassemble it further, just lift off the cluster at this point and the innards will be revealed to you, including another row of 1/8" balls (which will probably fall out) at the base of the freewheel, and two or three spring-loaded pawls which make the ratchet work.
You can now clamp the inner body in a vise by the pawl recesses, and unscrew the wheel. This is also how you remove a freewheel when you can't use a freewheel remover. Removing the inner body makes reassembly easier, but there is some possibility of damage from the vise jaws.
For re-assembly, you can use thickish grease to stick the balls in place while you reassemble the unit. With the outer part of the freewheel large-side-up, first insert balls into its bearing race. Don't fill the race completely -- leave room for two or three more balls. The tricky part is the pawls. In days of yore, there were special bobby-pin-like clips to hold the pawls compressed against their springs while you re-assembled the freewheel. These are no longer available.
Instead of the special clips, you can use a rubber band with a piece of thread looped though it. Assemble the pawls to the freewheel core, then wrap the rubber band around them to hold them against their springs. You may also be able to get the pawls to seat by holding the freewheel large-side-up and moving the core from side to side as you rotate it clockwise.
Once the outer part of the freewheel is more-or-less in place, use the thread to pull the rubber band out through the middle of the freewheel.
Sometimes it is possible to seat the pawls by carefully rotating the inner and outer bodes against each other in the freewheeling direction.
After seating the pawls, listen as you slowly rotate the outer body backwards. You should hear "tick, tock, tick, tock" if the ratchet in the outer body has an odd number of teeth -- one pawl engages at a time. If both engage at the same time, as on many SunTour freewheels, you should hear ticktick, ticktick, ticktick.
Use blue threadlock compound on the lockring threads, so it will not unscrew. It threads on counterclockwise, and tightening it will tend to loosen the freewheel from the wheel. Tighten the freewheel onto the wheel using a sprocket and chain whip or freewheel remover, so you will have enough purchase to tighten the lockring.
Most of these may be serviced in the same way as conventional freewheels. You'll need a fairly hard-to-find old-style Shimano special tool (TL-FH 40) to unscrew the cup, which is also the cone for the main bearings.
|Articles by Sheldon Brown and others|