Construction of Stage 2 was delayed by a number of factors and finally began in October 1973. A considerable amount of time was spent trying to determine an appropriate line for the motorway. Local farmers were angered by plans to route the road through good quality agricultural land, and the decision by the Scottish Office to await the publication of a report into the future of the Clyde ports also resulted in delay. Eventually a route near to the shoreline of the River Clyde was chosen and this was taken through a Public Local Inquiry. The route was completed in November 1975, almost five years after the opening of Stage 1. Stage 2 was built by Tarmac Civil Engineering Ltd. and cost £4.4 million, equivalent to more than £30 million today.

The completion of the bypass reduced traffic through Bishopton by over 80%. Today the section between junctions 30 and 31 carries almost 30,000 vehicles every day.