How to Fix a Slipping Chain on a Mountain Bike?
Source: https://www.sportsrec.com/7026765/which-gear-on-my-bicycle-is-1
Nothing can ruin a mountain bike ride quicker than an equipment malfunction. A slipping or skipping mountain-bike chain will hinder your ability to shift gears. The chain may be slipping due to an increased buildup of dirt or grime; a basic cleaning and lubrication procedure will often alleviate the slipping problem. According to the Mountain Bike Buzz website, worn links might be at fault if your chain continues to slip after being cleaned. If this is the case, you may need to replace the chain entirely.
Secure the seat post of your mountain bike into the clamp of the repair stand. Squirt some cleaning solvent onto a dry cotton rag. Hold the solvent-soaked rag around your mountain bike chain.
Rotate the pedals of your mountain bike to wipe the chain free of debris and grime. Apply a few drops of mineral-based chain oil into each of the links. Turn the pedals once more to see if the chain continues to slip.
Adjust the cable tension on the rear derailleur to ensure the chain remains centered on the rear cassette. Rotate the handlebar barrel adjusters clockwise to increase the cable tension. Turn the pedals rapidly to examine the alignment of the chain.
Examine the hanger of the rear derailleur to ensure it hasn't been bent. Clean between the rear cogs with a dry cotton rag. Tighten the hub bolts to prevent the rear cassette from moving freely.
Break your mountain bike chain with a chain splitter or remove the safety clip from the chain's quick-release link. Examine the link pins to identify any obvious signs of wear. Replace the chain entirely if it features broken or bent link pins.