Automatic transmission grinding

This is a fault within the transmission.

Within the transmission end housing are three gears. If any of the luck-nut are loosened (they are known to work themselves loose) it wold cause this problem. Prior to this the transmission should be whining pretty badly when in first or second speed while travelling.

Have this checked. If this is not the cause, then the transmission has to be rebuilt as it is leaking hydraulic pressure internally and this is not allowing the reverse shift fork from moving the reverse gear to the fully engaged position.