Graffiti vandals are causing mayhem on Melbourne's rail network by tampering with signals and train braking systems, breaking into driver's cabs and tagging windscreens while riding on the backs of trains.

The trail of destruction has been revealed by a small posse of tech-savvy trainspotters, who hack into Metro's internal radio network to expose raw and sometimes startling details about the daily disruptions to the rail network.

Blake De Sailly is highlighting problems with the Metro. Credit:Joe Armao

The group's publishing of radio communication between train drivers and controllers reveals the scale of Metro's problems with vandalised and defective trains, trespassers on tracks and close calls at level crossings.

Last week the group revealed a flurry of troubling incidents on one evening, including graffiti vandals breaking into the rear driver's cab on a Frankston train; drivers being warned to go slow because youths were putting debris on the tracks near Elsternwick; a family's near-miss with a train after dashing across a pedestrian crossing at Edithvale; a smashed train window; and vandals' attempts to kick in the door of a rear cab at Balaclava. All of this was reported in just over an hour between 7.50pm and 9pm on November 27.