More Reasons for a Sickly Drive train and How to Cure it
Part two of "Why Does My Chain Skip", goes into some of the more serious problems that will cause a chain to skip or slip due to problems with the ratchet system or worn out drive train components. Even if your chain is not skipping now it is good to know what conditions can cause a chain to skip. This will help you take action to slow down the process of wear and tear and to more clearly identify a drive train that needs some attention.
My gears slip forward making very little noise.
The Cause of the problem:
A slipping chain that gives you the "silent treatment" is usually an indication that the ratcheting mechanism at your rear wheel is having problems. Two basic styles of rear wheel systems exist. They are the cassette and the freewheel. A freewheel has cogs that thread onto a freewheel body and the freewheel body threads onto your rear hub. A cassette has cogs that slide onto a cassette body and the cassette body is bolted onto your rear hub. The most common ratchet system for both of these styles (freewheel and cassette) is that of a group of spring loaded pawls that engage into circular housing of peaks and valleys. This mechanism works just like a ratcheting socket wrench or a casting style fishing rod.
Things that can interrupt the ratchet mechanism are problems with the thickness of the grease inside the body, water that has frozen inside the body, and stripped cogs on the body of the freewheel or cassette.
From a problem with the thickness of the grease inside the body:
If you have an older bike or you have just repacked your hub with new grease, the stickiness of the grease may be overpowering the strength of the springs under the pawls to engage the freewheel or cassette body. This problem gets worse in colder weather as the grease will be more like peanut butter and less like cooking oil. You will pedal but the rear wheel will not move.
For an older hub (two years or older) with old grease the best course of action is to get at the outer gap of the body (where the cog platform meets the hub fitting), flush the body with solvent and add new lubricant. Lubricant that is as thick or slightly thicker than your chain lube will work best. If you have just added new lube and it is too thick you can flush it and apply a thinner lube or you can add a thinner lube and work it into the body until it spins more freely.
If water has frozen inside the body:
If you have ridden in the rain or washed your bike recently and the temperature is below freezing, you may have water freezing the pawls shut in the cassette or freewheel body. A quick fix is to get the bike warm. A hair dryer can speed up this process. Sometimes this heat is enough to evaporate any moisture that may have accumulated inside the body. If the problem persists or you want to make absolutely sure that there isn't any moisture in the body go ahead and flush it with solvent and add fresh lube. This should displace any water that has accumulated (remember, oil hates to be around water and vice versa).
Stripped cogs on the body of the freewheel or cassette:
Occasionally a cog will spin on the body because it has stripped out. This is a more common problem with freewheels than cassettes, but it does happen every once and a while to cassette cogs.
Solutions are to replace the offending cog and hope that it meshes with your chain. If it doesn't mesh, it will skip and you will need a new set of cogs and a new chain. Replacing all the cogs and the chain might not be a bad idea for cases of this nature because this problem may be an indication of a well worn drive train that will start failing piece by piece.
My chain skips only when I go up a hill or put a lot of pressure on the pedals.
The Cause of the problem:
This is a common occurrence when one component of a drive train has just been replaced or a drive train has been used so much that the chain skips over the top edge of the cog teeth.
Every time you ride you make your chain longer due to the force of pedaling. A new chain will measure exactly one chain rivet or pin for every half inch. A chain that has thousands of miles ridden on it will have pins that almost match up on every half inch mark, but by the time you get to twelve inches the twenty-fourth pin will be around twelve and one eighth inches. As a chain stretches it wears the leading edge off of the cogs and chain ring teeth. Mixing a new chain with old cogs is a problem because the new chain usually doesn't mesh with the worn gears and skipping results. (worn gears will look like shark fins or will hook slightly on the worn edge) Frequently lubricating your chain helps to keep the loose metal from worn teeth acting like sandpaper and speeding up the wear process.
Usually skipping presents itself in your favorite gear, as this is the gear that wears out the first. Other problems associated with a worn drive train are bushings coming out of the chain, bent cog or chain ring teeth, and individual teeth breaking off of cogs or chain rings. All of these problems can cause a chain to skip while under pressure.
The first step is to rule out that you may have a tight link. (See part one)
Once you are sure that you don't have a tight link, inspect the chain for missing bushings (the washer between the side plates) and look for missing teeth on the cogs and chain rings. Sometimes you can replace a few links in a chain to solve the missing bushing problem, but you more than likely will need a new drive train soon. For broken teeth you will probably need to replace the cogs and the chain as new cogs will skip with the old chain.
If no teeth or bushings appear defective take out a ruler and measure your chain setting up the chain pins on the half inch marks. If at twelve inches the pin is past the twelve and one eighth mark, your chain may have stretched long enough that you will need to replace the cogs and chain together and quite possibly the chain rings. Another thing to check is chain on the large chaining (at the pedals) to see how tightly the chain hugs the ring. If you can easily lift the chain off of the big chain ring, your chain has stretched and it may be time for a new drive train.
Replacing your drive train is the bicycle equivalent of replacing all the belts and hoses on your car every 70,000 to 100,000 miles. It can be an expensive undertaking (starting around $50 and going up) but luckily it only needs to be done at far reaching intervals. It can also be a source of pride. " I wore out my bike, before it wore me out. "
When I put pressure on the pedals my gears slip forward
Cause of the problem:
This is an indication that you have a badly worn chain ring. This can be one of the most violent skipping occurrences on a bike since the pedals will grind forward on half pedal stroke and engage. Also a bent tooth can cause a cascading effect and make this happen.
Inspect the chaining from above your seat and look for bent teeth. If you find bent teeth you can straighten them with pliers or a large crescent wrench (use caution as some chain rings come new with bent/torn teeth to aid in shifting). You can also remove your rings and hammer the teeth flat over a flat surface (not the dining room table unless you live with other cyclists or you live alone).
If you don't see any bent teeth, look at the chain rings from the side. If the teeth are shaped like a shark fin then the ring is more than likely worn enough that this is causing skipping. Small and medium sized chain rings usually wear out first. They go through more revolutions and the tighter circumference is harder on the metal. More than likely, you will only need to replace your smaller chain rings due to this fact. Eventually the large chain rings wear out also.
Sometimes on a triple crank set you can salvage the smallest chain ring by reversing the direction of the ring on the crank. The leading side of the teeth becomes the following edge and vice versa. The old ring will perform like a new ring. This only works for the smallest rings because the middle and large chain rings have a beveled side to aid in shifting.