I just got an e-savage and it is my first new truck. I dont know much about rc just getting started. ne way....I changed my servo from plastic to metal now it makes a humming sound and sometimes it wont turn!!! any ideas?

Is it a hitec servo?

well, first things first, in order to be able to help you we need more information about the servo that you have installed into the truck. first question i want to know is is it digital? and if it is can you give me the specks on it. it may not be powerful enough to turn the wheels of your monster truck. so If you can get the specs on the servo anyone in hobbytalk would be more than happy to tell you what the problem is.

HOPE THIS HELPS
Sean Scott