Description of the malfunction:
The pedals and the chain spin freely and move the cogs at the back, but the rear wheel remains stationary.
The hub appears to be in permanent “coast mode” even during forward pedaling.
The root of the problem:
The pawls of the hub are stuck due to hardened grease and accumulated dirt. This state prevents them from springing back and engaging the ratchet ring of the hub. As a result, the drivetrain fails to deliver power to the rear wheel.
Note: If the bicycle is older, chances are that it has a freewheel rather than a cassette freehub. In that case, the ratcheting mechanism will be in the freewheel rather than the wheel’s hub. In both cases, however, seized paws are the source of the malfunction.
The figure above illustrates the proper operation of a cassette hub when pedaling forward.
When the chain and pedals are spinning forward, the pawls of the freehub body open and bite against the teeth of the ratchet.
As a result of that “union”, the power of the cyclist is transmitted to the rear wheel.
During backpedaling, the freehub body is rotating anti-clockwise, and the pawls are sliding against the teeth of the ratchet (fig.2)
During coasting, the ratchet ring keeps sliding against the pawls, but the freehub body and the cogs remain stationary (fig.3)
When the hub is seized, the pawls remain semi or fully closed. This keeps the ratchet and consequently the rear wheel disengaged.
The illustration above shows seized or disengaged pawls. If the pawls cannot open (spring back) due to contamination or a mechanical failure, they will remain in a closed position and will prevent the normal functioning of the hub.
The main ways to fix this problem are:
1. Clean the Hub (lazy method)
The quickest and also the cheapest way to free a seized hub is to clean it without disassembling it.
The steps are as follows:
1. Remove the wheel from the bike.
2. Remove the cassette (you will need a cassette removal tool for that)
3. Clean the hub’s free-body with a dry brush to push away some of the dirt.
4. Spray a degreaser such as WD-40 or a brake cleaner into the opening (image below) of the hub.
Keep turning the hub’s free-body in both directions while spraying the zone. The goal is to spread the cleaner onto every paw.
Note: The pawls of the free-hub are located right behind the body which is why you have spray this area.
Repeat the procedure a few more times. If the hub isn’t broken, at least some of the pawls should begin to bite. Ideally, you will feel all of them engaging as you spin the free-body clockwise (pedaling forward).
This method has a downside, however. The solvent will clean the gunk but it will also remove some of the hub’s lubrication and decrease the lifespan of the component.
To avoid this, it’s recommended to lay the wheel horizontally (freehub body facing up) and then lubricate the hub through the same crack with light oil.
If you use heavy oil, the same problem may occur because the denser lubricants can immobilize the pawls.
If you don’t want to bother with two different chemicals (one for cleaning, one for lubrication), you could consider using a product that does both. A common example would be Boeshield T-9 Bicycle Lubricant which cleans and lubricates bike mechanisms.
Note: WD-40 is not a good long-term lubricant and should be used in conjunction with another product or else the hub will be running “dry” and will have a shorter lifespan than normal.
5. Clean the hub with a dry cloth, install the cassette, and put the wheel on the bike.
What About a Freewheel?
If you have a freewheel, the same procedure could be followed. The only difference is that you will have to remove the freewheel from the hub and spray the degreaser at a different location.
Note: You will need a specific freewheel removal tool different from those designed for cassettes.
2. Overhaul The Hub
In most cases, the procedure described above would return the hub to its normal operation.
But if you want a more thorough cleaning, you will have to disassemble the hub and take off the freehub’s body via an Allen key.
Once the freehub body is off, degrease it fully, clean it and then lubricate it with grease designed specifically for hubs.
This method is a lot more time consuming and requires more tools (cone wrenches, regular wrenches, Allen keys, tweezers or thin pliers…etc.) and skills.
However, it’s worth doing, especially if the hub is expensive.
If you’ve never done it before, you could search for a video online and hopefully find the specific hub that you have.
Note: If the rear hub or the bike itself is under warranty, do not disassemble the hub yourself. Bring it to the mechanics.
What About a Freewheel?
The freewheel can also be taken apart and serviced. But since freewheels are cheap, a complete overhaul makes financial sense only when you already have the necessary tools, cleaners, and lubricants.
If you bring the freewheel to a service shop, they will probably offer you a new one because it will be cheaper than paying for servicing the old unit.
The Pawls Are Engaging But The Wheels Still Isn’t Spinning
In some rare scenarios, the pawls will engage normally, but the wheel still won’t turn.
The most common culprit is a broken ratchet ring rotating in the hub shell.
The ratchet ring is a metal circle with a high number of teeth/engagement points against which the pawls of the hub bite.
If the ratchet ring is disconnected from the hub’s enclosure, it will be impossible to transfer power to the freewheel.
In most cases, the ratchet ring is either threaded and screwed onto the hub or press-fit via a special tool that only the manufacturer has.
If the ratchet ring is the culprit, the best solution is to replace the hub or freewheel entirely as it’s very difficult to remove the ring and install a new one.
Cold Conditions Damage The Hub
If the grease in the hub is old and contaminated, it will allow water to reach and surround the internals. When the temperatures drop, the water freezes and so do the pawls. The result is a non-operational hub.
The textbook solution is to disassemble the hub, clean it and replace the grease with one that can sustain lower temperatures.
If the problem occurs suddenly, heating the hub should restart it. One of the options is to disperse hot liquid on it.
Broken Pawls and Springs
If the pawls and springs of the hub break, the same problem would occur because there will be nothing to grab onto the ratcheting ring. When that happens, the only solutions would be to replace the pawls & springs or the entire hub.
If you have a generic hub, chances are that you won’t find spare parts fort it. However, if you have a high-end model, you may be able to buy pawls and springs separately.
Thankfully, pawl failure is pretty rare, especially if you don’t ride your bicycle in extreme conditions.
Fixed Gear Bicycles Don’t Have This Problem
Fixed gear bicycles don’t use a hub with a ratcheting mechanism. In consequence, there are no pawls that can seize. If you have a single speed bicycle with a flip-flop (one side is a freewheel, the other a fixed gear), you can flip it and use the fixed cog while looking for a solution to the problem.
Note: This is a temporary solution.
If you’re new to fixed-gear bicycles, you will need a certain amount of time to get used to the set-up. Hence why it’s not advisable to go crazy with your itinerary right away.
What About Internally Geared Hubs?
If you have a geared hub displaying this issue, you will have to send it for repair to a reputable bike mechanic because internally geared hubs are complicated and difficult to service on your own.
Very often, even professional bike mechanics loathe the thought of fixing an internally geared hub. For that reason, it’s common to just swap the internals of the hub without even trying to troubleshoot it.
Frequently Asked Questions
How long should a rear hub last?
It depends on the quality of the hub, its use and the climate conditions. A cheap hub that’s ridden hard in “unfavorable” weather could disintegrated in a month or less.
In general, however, a quality hub should last at least 4-6 months before servicing even if it’s abused pretty heavily.
If you use your bicycle mainly for commuting, a decent hub can easily last 10,000+ miles/16093 km+ without heavy signs of malfunctioning. The usual signs of wear are annoying new noises and play.
In my case, I have a low-end Shimano rear hub which has been with me for years (about 9,000miles/14500km) and it’s still working fine.
Why are expensive hubs so much louder than the cheap ones?
High-end hubs are louder because they tend to have more pawls, stronger springs and ratchet rings with extra engagement points.
You can learn more about this topic here.