Altus is a bicycle component group manufactured by Shimano. A component group includes nearly all parts of the bike except the frame, seat, wheels and forks. Front and rear derailleurs are part of the Altus group. When you shift, the derailleurs move your chain allowing you to change gears. The rear derailleur works with the right hand shifter and the front derailleur works with the left hand shifter. The installation of new Altus derailleurs can be done at home with a few tools.
Mount your bike in the bike stand with the drivetrain (the side your gears are on) facing out. This makes it easier to work on the bike.
Open the clamp of the front derailleur and position the derailleur onto your down tube (the part of the frame extending from your pedals to your seat) so the outermost portion of the derailleur cage lines up (when looking straight down) with your largest chainring (front gear). Move the derailleur up or down until the cage is one millimetre above the largest chainring. Tighten the bolt on the clamp of the derailleur to hold the derailleur in position.
Locate and remove the hangar bolt (the large bolt at the top) from the rear derailleur. Attach the rear derailleur to the bike frame in the hole near your cassette (rear gears). The arm of the derailleur with the jockey wheels hangs downward. Insert the bolt and tighten it until the derailleur is secure.
Thread the new chain around the jockey wheels of the rear derailleur, over the cassette, over the largest chainring and through the cage of the front derailleur. Connect the chain by pressing the chain link pin that came with the new chain through the two end links until the links are secure.
Thread the shift cable that runs from the left hand shifter to the front derailleur's cable anchor bolt located at the top of the derailleur near the clamp. Loosen the cable anchor bolt and thread the cable through. Tighten the bolt until the cable is secure. Place a new end cap onto the end of the cable and crimp it with the crimping tool to keep the cable from fraying.
Thread the shift cable that runs from the right hand shifter to the rear derailleur's cable anchor bolt located at the top of the derailleur near the hangar bolt. Loosen the cable anchor bolt and thread the cable through. Tighten the bolt until the cable is secure. Place a new end cap onto the end of the cable and crimp it with the crimping tool to keep the cable from fraying.
Having another bike or bike manual on hand will help remind you how the chain travels around the derailleurs and gears properly. Using a chain link tool can help if it is difficult to insert the new chain link pin. This article assumes you did not remove your shift cables before you installed the new derailleurs. You will need to adjust the tension of your cables after the installation.
Be sure that all bolts are secure. If a derailleur or cable comes loose while riding it could cause you to crash.