Tyler Betteridge
New member
Ok so I have been having some serious problems with the derailer on my mountain bike. I have a Trek 3900 and for some reason the rear derailleur randomly does not catch on the back wheel of the bike. It is not the chain that is slipping because i am still able to pedal and if i continue to pedal the chain causes the derailer to spin, but it spins freely and doesn't make the rear tire spin with it. The problem seems to happen in the morning, after my bike has been sitting all night, or when i try to stand up on the pedals and pedal really hard. It also happens sometime if i am pedaling and then come to a stop and then tr to pedal again and it doesn't work, I've taken the bike to two different shops. The first time the guy said it might be my gear cables so he took them out and replaced them. This fixed the problem temporarily but it started happening again like a month later. At the next shop I took it to, the guy took a look at how the derailer was aligned and made a few minor adjustments but overall couldnt tell what was wrong with it. This problem is getting dangerous and has almost caused me to wipe out a few times. I want to fix it but don't want to have to pay to bring it to a shop unless i absolutely have to. PLEASE HELP ME!