Dangerous Gear Malfunction.

[oil27]

My MTB suddenly began to forward peddle by itself while I coasted. It was violent and wobbled me around. Fortunately I was on a back street. This happened several times since. Sporadicly it just catches. I am sure there is a fault inside the back wheel axel inside the the cogged part, in the gear really.

Can it be fixed or should I just by a new bike for this one was really very cheap? How can I fix it?

 

[dennis dee]

It should freewheel when you coast. Freewheel cogsets with damaged ratchet mechanisms may do this. Have your LBS inspect it coz maybe the whole hub needs to be replaced.

 

[daveornee]

Originally posted by oil27
My MTB suddenly began to forward peddle by itself while I coasted. It was violent and wobbled me around. Fortunately I was on a back street. This happened several times since. Sporadicly it just catches. I am sure there is a fault inside the back wheel axel inside the the cogged part, in the gear really.

Can it be fixed or should I just by a new bike for this one was really very cheap? How can I fix it?

If it's a cheap one, it has a freewheel. The freewheel has a ratchet and pawl. If that mechanism is faulty, a new freewheel is in order.
Some cheap bikes have a freehub system. In that case, replacement of the hub is in order.... but it is likely that a whole new rear wheel could be cheaper... saving the old cassette.