How to adjust shimano rear derailleur on mountain bike?

To adjust a Shimano rear derailleur on a mountain bike, follow these steps: 1. Start by shifting the chain onto the smallest rear cog and the smallest front chainring. This will relieve tension from the derailleur. 2. Locate the barrel adjuster on the rear derailleur. It's usually near where the cable housing enters the derailleur. 3. Turn the barrel adjuster counterclockwise to release tension on the cable. 4. Next, manually pull the derailleur cage towards the smallest rear cog. This will ensure that the derailleur is properly aligned. 5. While holding the derailleur cage in place, pull the derailleur cable tight and reattach it to the derailleur. Make sure it is securely fastened. 6. Shift the chain back onto the smallest rear cog and the middle chainring. 7. Now, turn the barrel adjuster clockwise to add tension to the cable. Shift through the gears to make sure the shifting is smooth and accurate. 8. If necessary, fine-tune the adjustments by making small adjustments to the barrel adjuster. Turning it counterclockwise will move the derailleur towards the smaller cogs, while turning it clockwise will move it towards the larger cogs. Remember, adjusting a rear derailleur can be a delicate process, so it's a good idea to refer to the Shimano technical manual for your specific derailleur model.