The A740 originally started in Paisley town centre, heading north west out of town on Greenock Road - a route now taken by the A726. However, with the construction of the M8 and Glasgow Airport, the A726 now takes a detour around the south west end of the runway and so passes through Junction 29 of the motorway; the ex-A740 is now lost under the airport runway. Beyond the airport, we rejoin the old route and cross the Black Cart Water at Barnsford Bridge.
The A726 now follows the A740's old route past the B790 junction and across the A8 Greenock Road to meet the unclassified Old Greenock Road. Here the road dog-legged to the west onto Barrhill Road, along which a number of housing schemes (East Craigend, North Barr amongst others) have since been built. Barrhill Road, and so the old A740, turns left before the modern roundabout on the A726. This may now be a dead-end, but across the A726, the old route can once more be picked up as it runs down to the old ferry slip for the Erskine Ferry.
The A740 crossed the Clyde by the ferry, for the very short stub of Erskine Ferry Road to lead it up to its terminus on the A82 (current A814).