Derailleur Restoration Tutorial
Unless your bike building hobby allows for an unlimited budget, you will probably end up salvaging parts from various used or worn out bicycles. Even a beat up ten dollar yard sale bike will yield at least a few good parts and components, and with a little work you can often restore many components to a like-new state. Some of the components such as levers, cranks, wheels, and derailleurs may only need a good buffing and re-greasing, and as you know, these parts can be quite expensive to purchase new. I almost never purchase new components for a project, especially when it is in the prototype stage, but I have learned how to bring old and tattered parts back to life. In the 25+ years of my bike building adventures, I have never purchased a new derailleur, but have amassed a good collection from scrap bikes. Let's have a quick look at what it takes to bring some life back to a typical yard sale bike rear derailleur.
There are two distinct types of rear derailleurs - "hangers" and "frame mounted". A Hanging type derailleur includes a slotted plate that matches the slot on the rear dropout, allowing the rear axle nut to hold it in place. As shown here, this plate matches the shape of the rear dropout slot, and is held tight to the frame by the axle nut washer. This type of derailleur mounting system has been around forever, and is more popular on lower end bicycles and older bicycles, which are the type you will often find in your scavenging.
A bolted on rear derailleur, like the one shown here, does not include a slotted dropout plate, it simply has a mounting bolt. This type of derailleur requires a mating hole on the frame, which will be positioned just under the right rear dropout. Functionally, both derailleur types function the same way, and only differ in the fact that the hanging type includes the mounting plate in its design. When making a trike or a quad, the hanging type may be easier to work with since you can cut and weld the hanger plate for adaptation to a new mounting system. You can hack a bolt on frame mounted type as well, but will have to chop the mating mounting plate section from the frame.
Here is a frame mounted derailleur, showing how the main bolt is fastened directly to the frame. This type of derailleur is usually found on higher quality cycles, and is a more mature design that the hanger type. A frame mounted derailleur requires a mounting tab installed on the frame as part of the right rear dropout.
Another distinct difference you will see between rear derailleurs as you begin to build up your parts collection, is the spacing between the two idler wheels. This idler wheel spacing will vary greatly between models and brands, but typically, one would classify a derailleur as either a long cage or short cage. Because the two idler wheels act as a tensioning system to pick up the return chain slack, in theory - the longer the cage, the more chain that can be pulled back. So to simplify this even more, a short cage derailleur is usually used on a road bike, and a long cage will be used on a mountain or touring bike, since it will have a much larger range of gears. A larger "range" of gears means more difference between the diameter of the front and rear chain rings. I almost never use a short cage rear derailleur, because I like to have a full range of gears, which makes hill climbing easier, and downhill sprinting more fun. The derailleur shown in this image is on the extreme side of the short cage variety. This dude is probably from an old 1980's ten speed.
So to clean up a derailleur and bring back its luster, you will need some basic tools as shown here; a small adjustable wrench, screwdriver, wire brush, fine steel wool, a rag, and some Varsol or degreaser. In extreme cases, you make need some fine grit sandpaper to remove rust.
Start your cleaning adventure by removing as much grease as you can using an old rag and some degreaser. You may find that your derailleur will come back to life with just a good external cleaning, but it won't hurt to continue on and regrease the wheels as shown later in this tutorial. I like to do a full clean and regrease on a derailleur after every year of service, as this gets rid of the "squeaks" and ensure smooth shifting.
The tension spring shown here, is wrapped around the main bolt, and it is responsible for the pulling back action that picks up the slack in the return chain. This will be one of the dirtiest parts of the derailleur, so give it a good wipe down with the degreasing agent and a rag.
After a good wiping down, my old derailleur doesn't look too bad, but it is still tarnished, and the idlers are stiff when I turn them. Idlers have only bushings for bearings, so once the grease dries up, they will seem stiff, and this friction could cause your chain to skip. Once the grease has completely dried out, the idlers will begin to squeak, which is highly annoying, especially on a Lowracer, where your head is so close to the rear wheel.
Ok, after wiping away as much loose grease and dirt as you can, it is time to remove the easy to disassemble bits and give it a full cleaning and regreasing. If you have a hanging type of derailleur, remove the guide build and plate that helps align the slot with the rear dropout. It's a good idea to remove these loose parts as you could easily loose them when cleaning and handling the derailleur. Be warned... if you drop a needed bolt on the ground, Murphy's Law has shown that you will not find it again until you have either replaced it, or until you no longer need it!
Another small piece that should be removed before cleaning is the cable clamp and nut. Turn the but in the counter clockwise rotation until it is freed, which will in turn free the small square cable clamping plate. Some derailleurs will have just a washer instead of a small square plate.
The purpose of the clamping washer small plate shown here is to crush the end of the shifting cable to the spring loaded moving section of the derailleur so that when the cable is pulled, it in turn pulls the moving section of the derailleur. This is how the idlers are moved along the rear chain rings, allowing the chain to be moved from one chain ring to another.
There are two more bolts to remove in order to allow a full cleaning of the derailleur, and these are the bolts that hold the cage and idler wheels in place. You can use an adjustable wrench or the appropriate size box wrench to remove the two bolts. Start with the bolt you can easily reach as shown here, turning it in the counter clockwise rotation until it is loose enough to turn out the rest of the way with your fingers. The bolt is also the axle for that idler wheel, so it may fall out once the bolt comes out. Don't let the idler fall on the floor, as it also includes 3 smaller bearing components that are easy to lose.
The second cage bolt is not as easy to reach with a wrench because you have to pull the main spring back and hold the cage in place while you loosen the bolt. A good derailleur spring can snap back if you lose your grip, and give you a good pinch, so take caution when pulling back on the cage. You could jam a screwdriver in the cage and keep it propped open, but just be aware that if the unit springs back suddenly, you will certainly emit very crude words as your finger is clamped!
once again, turn the bolt in the counter clockwise rotation until it is loose enough to turn out the rest of the way with your fingers. This time the idler wheel will fall free along with the back side of the derailleur cage, which was sandwiching all of the parts together. The two sections of the derailleur cage act as a channel to prevent the chain from bouncing off the idlers under extreme conditions as well as a bolting system for both idler wheels.
With the two idler wheels removed, you now have the rear derailleur taken apart as much as you need in order to give it a good cleaning and full regreasing. You should have three small bearing components that go along with each idler, which are a cylindrical bushing and two end caps that hold in the grease.
The small cylindrical bushing is typically made of a soft metal like brass, and this is the bearing that the plastic wheel rides on. When the grease dries up, the wheel will either seem stiff to turn, or it will be so loose that it squeaks, which is an all too common sound on an old unmaintained bike. A plastic surface riding on a bushing may seem odd, but since there is almost no tension on the return chain, the friction cause by this system will be very minimal.
The two small discs that go along with the idler wheels keep the idlers aligned on the bushing and also create a seal that locks the grease in the open reservoir section of the plastic idler. The idea here is that the idlers are greased once at the factory and are good for life, but in reality, the grease does seem to dry out after a few years. Note the ridge on the discs, which are placed into the idlers to form a kind of seal to keep the grease from leaking out.
Here, I have placed the bushing and end caps onto the idler and then put the axle bolt back through, showing how the five components work together. Because the bushing is slightly wider than the hole through the idler, it doesn't matter how tight the two end plates are pushed towards the wheel, they will never rub on the plastic section. At this point, all of the grease has dried up, to the wheel is stiff to turn. A properly greased rear derailleur idler will turn smoothly, but not spin freely. If it spins freely, then the grease has completely dried out and the plastic bore has probably worn somewhat. This will cause a squeaky wheel, which as we know from the old saying "gets the oil".
Here is my garden variety rear derailleur with the idlers and small bolts removed. It isn't too badly rusted or damaged, but does need a good shine in order to earn the right to hang from the back of the new trike I am currently building. And there is no way I would tolerate a squeaky transmission, so a full regreasing will also be in order.
At this point, you have 15 or more parts to clean up before reassembling your derailleur, but this process won't take longer than a few minutes, which is why it's a good idea to do this maintenance once per riding season on your transmission system. Reassembly will be a breeze as well because you really can't put the derailleur back together incorrectly. The pieces only fit together one way.
The two plastic idlers will most likely be caked with dried grease and grunge from both the chain and the original factory grease that has dried up from inside the bushing. If the teeth on your plastic idler wheels look deformed or worn, then you may need to salvage another set form a different derailleur (most are compatible with each other). The teeth should have a round profile with a squared off top, similar to the profile on the rear chain rings. If the idler wheel was completely seized in the derailleur gage, then the plastic teeth may have been sawed off by the chain skipping over the top. Typically, there is no torque in the idler system, so the plastic gears should not have been worn very much.
A little cleaning agent like Varsol or paint thinner should take that caked grease right off the derailleur idler wheels. Just dip an old rag in the cleaner, and then wipe away the grease, dirt, and grime. Engine degreaser might work as well, but read the label to make sure it is compatible with plastic, or you may melt the idler.
Clean inside the hollow section of the wheel where the metal cap will sit. You can do this by using a corner of the rag with the cleaning agent applied. You will be adding some fresh grease in this area, so you don't want it all gummed up with old grease and grit. If the dried grease is really stiff, use the edge of a small screwdriver blade to dig it out and then try the cleaner.
Another method that can be used on stubborn grease and grit is a wire brushing. Hold the wheel and run the wire brush over the edge as shown here, which should remove even the most caked on dried up grease and grime. Consider wearing your work gloves when using a wire brush close to your fingers, as the bristles are sharp like needles and could give you a puncture if you brushed your finger with enough force.
With a bit of scrubbing, your plastic idler wheels will come back to a like-new look. If there is any damage done to the sprocket teeth, you will be able to see it clearly now that they are clean. If you need to replace the idlers, you can take a set from another derailleur, as most of them have the same diameter and center bushing bore. Ultra or Mega Range type derailleurs might have a larger idler wheel, and since the cage is build around the diameter of the idlers, you won't be able to use a larger wheel to replace a smaller one.
The derailleur cage sections can usually be cleaned up using a wire brush, but if they have lived outdoors for many years, you may need to attack the job with steel wool or even some fine grit sandpaper. If you end up sanding off a bunch of rust, then you could even paint the cages, something I have done to give a derailleur a unique look.
Clean the main body using the rag and then wire brush if necessary. If you are really hard core, and just want to see how things work, you could go as far as popping off the plastic caps and retaining rings to take apart the derailleur even further, but for a basic cleaning this really isn't necessary.
Steel wool does a great job of cleaning up slight surface rust without taking out too much of the shine from the original metal. You will have to scrub the entire surface once you start in order to make it look even though, since the steel wool will take off a layer. If the rusted area hasn't pitted the metal too much, the steel wool should do a good job. For seriously rusted metal, you will have to resort to using sandpaper or emery cloth.
There is no nut to fasten the idler bolt since the other side of the derailleur cage is threaded, and it acts as the nut. Notice how the derailleur cage is shaped to be a mirror copy of the other side; you need to match up the two cage sections so the pattern aligns on each side. Most likely you won't be able to install the cage sections incorrectly, but if you do, it will be obvious.
Tighten up the bolt with your fingers until the cage sections are held firmly together. As shown here, there is often a small bent tab included on one of the cage sections; this has the purpose of keeping the chain from bouncing off the idler under extreme conditions. If the chain were to bounce off of the idler, it could possibly fall right out of the derailleur cage, so this bent tab prevents that situation.
Putting in the other idler bolt is a little more challenging as you probably recall when taking apart the derailleur. You have to pry back the cage against the main spring and avoid pinching your fingers between the cage and derailleur body as you insert and tighten the bolt. You might want to try placing some object like a screwdriver into the cage once its pulled back in order to hold it in place. Either way, just be careful not to let the cage snap back on your fingers, because I can assure you that it isn't fun!
Now you must tighten up the bolts using the same wrench you used to remove them. Tighten the easy to reach bolt first, turning it in the clockwise direction until you can't tighten it anymore. You can't over-tighten the bolts, since the bushing is preventing the sides from pressing against the idler wheel.
Reinstall the alignment tab and bolt as shown here, positioning the tab so that the D-shaped side is facing the slotted hanger plate. This tab is designed to slide into the dropout and lock the derailleur into the right angle and position on the frame. A frame mounted derailleur doesn't need this tab since it is automatically placed in the correct position on the frame.
Install the cable locking tab as shown here, with the bent side facing down, or towards the derailleur. The purpose of this tab is to grip the bare end of the cable, acting like a vise as the nut is tightened down. Your hardware may differ, but the general idea is the same; the cable is pressed between two plates or a washer in order to lock it down.
This photo shows the position of the cable locking tab on the derailleur. The bare cable is slipped between the plates, and held in place by the friction introduced by the tightening of the nut. The initial tension on the cable while the derailleur is on the idle position determines the alignment in your shifting system, so you will be using this cable fastening system a few times while tuning up your transmission.
Well, that's about all there is to cleaning and lubricating a rear derailleur. You should be able to revive the squeakiest, dirtiest derailleur to like new condition with a little work. Keeping your transmission parts in good working order will ensure a quiet and efficient ride, so this maintenance is a good thing to do on a regular basis. Soon this rebuilt derailleur will be hanging off the back of a new home built recumbent racing trike, allowing me to climb the steepest hill in low gear, while giving me the top gear needed to reach incredible speeds back down the hill.
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