I have an older Bachmann Spectrum CSX Dash 8 which has some drive issues.  The motor runs well but the transmission of the power to the front and rear drive trucks is intermittent.  It appears that the drive shafts or connections of the drive shafts are not engaging with the truck drives.  The truck assemblies seem to run free separately.  Any clues as to what parts to replace or if it the best bet is to send to Bachmann service for repair.  Don't want to dig into the unit if it is better to just use the lifetime warranty for Bachmann loco's for their drive units.