Step 1: Remove the wheel and undo the derailleur cable

Change the gears to the smallest sprocket (or your highest gear). Flip open the wheel’s quick release system to remove the wheel. Loosen the cable crimper bolt and cut the cable end cap off. You can use carpenter’s pincers, a cable cutter or a Dremel with the Cut-Off Wheel (409) accessory to do this – they’re all great for preventing the cable from splitting. Unthread the cable from the rear mech. You are now ready to remove the chain.

Step 2: Unthread the chain and remove the derailleur

Look closely at how the chain is threaded into the derailleur before taking it off. Unscrew the upper pulley bolt with a combination spanner to detach the chain. Pull the chain off the pulley, leaving the derailleur free to be removed. Unscrew the main bolt of the rear mech hanger. Unthread the chain and remove the derailleur, while you support it with your hand so it doesn’t fall down.

Step 3: Disassemble the derailleur

Each derailleur will come apart slightly differently. Unscrew the different derailleur parts, starting with the pulleys. Make sure you are using the right size tools for your derailleur’s screws and bolts – you’ll need a set of Allen keys, a Phillips screwdriver and a selection of combination spanners. By keeping all parts neatly organised, you don’t risk losing anything, and you can keep track of what goes where. You can even take a picture of all the parts when they’re laid out, to use as a reference later. This makes reassembling the rear mech much easier.

Step 4: Clean and degrease the derailleur parts

Scrape the worst of the muck and dirt off the different parts of your derailleur using a slotted screwdriver. Wipe them on a cleaning cloth and drop them into a small container filled with degreaser. Check beforehand if your degreaser needs to be diluted with water first. Leave the components to soak for 5 to 10 minutes, and then clean each one using a small brush. Rinse the parts in a container filled with clean water, and then dry them with a clean cloth. Your derailleur is now squeaky clean and ready to be de-rusted.

Step 5: De-rust your derailleur parts

No one likes a rusty bike. So, once your parts are nice and dry, get your Dremel kit out. Clamp the Dremel Multi-Vise to your work surface and secure the Multi-Tool to it. Insert and tighten the Brass Brush ( 535 or 537 ) and run each part carefully against the spinning brush to remove all signs of rust. Brass Brush 535 is your go-to accessory for general de-rusting, whereas Brass Brush 537 can get into small grooves and other hard to reach spots. The maximum RPM for de-rusting is 15,000.

Step 6: How to polish the derailleur parts

Now’s the time to make your derailleur parts shine as if they’ve just come out of the box. It’s easy. Just insert the Mandrel (401) and screw on Polishing Point 422 or Polishing Wheel 414 . Our Comparative Fact Sheet will help you find the right accessories. Hold the spinning point or wheel briefly against the Polishing Compound (421) and use the impregnated accessory to give your parts a thorough polish. Don’t forget the little screws; they deserve a little sparkle too.

Step 7: Put the derailleur back together

Start by greasing the pulley wheels with ball bearing grease, using a paintbrush to get in all the nooks and crannies. Then, carefully put all the parts back in their original place, working in reverse order to how you took it apart (step 3). Reattach the upper pulley wheel, but leave the lower wheel until step 9. Depending on your derailleur’s age and make, the lower (tension) and upper (guide) wheels may differ, so make sure you keep them apart. It’s also important to place them back into the cage plate in the correct direction. Your pulley wheel may have an arrow on it to guide you.

Step 8: Install the derailleur

You’re nearly there now! Do a quick check to make sure the mech hanger is nice and straight; not bent or damaged. If it is, you might want to repair or replace that first. Now slide the rear mech onto the mech hanger, making sure that it is properly aligned so there’s enough space for the wheel to be slotted in later. Screw in the hanger bolt, and then thread the cable through the derailleur. Turn the bolt to secure the cable. Crimp the cable using a cable end cap and carpenter’s pincers.

Step 9: Put the bike chain and wheel back in place

Guide the bike chain over and around the cassette, and then thread it through the upper (guide) pulley. Next, guide the chain through the power pulley’s case, and then pop the lower (tension) pulley back in place. Insert the screw and tighten it. Slot the rear wheel back in place and tighten the quick release handle. On to the last step!

Step 10: Adjust the derailleur

The last step is all about fine-tuning the derailleur. With the bike in a bike stand, change the gears to the smallest sprocket (or your highest gear). Now adjust the derailleur while you spin the wheel by turning its high-limit screw using a Phillips screwdriver. Repeat this process for the lowest gear (largest sprocket) by turning the low-limit screw. Once shifting up and down goes smoothly and your chain runs quietly, you’re done. Give the derailleur one last wipe with a dry, clean cloth and you’re road-ready!