The Gelliwiog Shuttle was the name given to a short run from Dduallt station to Gelliwiog, on the then being constructed Deviation. The operation of this shuttle was an expensive necessity forced on the FR Co as a result of receiving a grant from the Wales Tourist Board. One of the conditions of the grant was that it must be put to public use within a year and it was going to be another two before the extended line could reach anywhere that a run-round loop could be installed. The solution was to use the former Hunslet mines loco Moel Hebog together with a specially constructed Carriage 110 which had driving controls in the Porthmadog end, as a Push Pull train.
Neither the loco or the carriage were finished when needed and it went into service on 26th May 1975 with panels missing on the loco and the carriage in primer and without glass in the windows. Work on it progressed on it when time could be found (sometimes in the evenings) but it was still not fully completed by the 1976 season.
The Shuttle was attached behind the train engine on the first up train of the day, and once at Dduallt it operated from a separate platform on the east side on the up line. At the end of the day it was reattached to the rear of the last down train.
It was not very successful in terms of revenue received (an additional fare was charged) as passengers were reluctant to leave their seat on the main service train, but it satisfied the Wales Tourist Board.
The operation of the shuttle was terminated sometime before the line was opened to Llyn Ystradau