Police later named the missing pair as Jamie McClement and John Fury of Twechar. James Gibson, also of Twechar, apparently escaped from the vehicle and raised the alarm.
The bridge failed as record rainfall hit western Scotland: 80 roads were closed and only two bridges open over the Clyde because of flooded access roads. Traffic disruption made the task of emergency workers more difficult.
According to the Glasgow weather centre, the city received as much rain, about 4.5 inches, as would normally fall during the whole of December.
Strathclyde Chief Constable Leslie Sharp, who went on a helicopter tour of the region, said many families in the low-income area were not insured.
"Although they will be back in their houses before Christmas, it will take months to dry out," he said. "Their presents and Christmas decorations have all gone. There is going to be a lot of cold comfort this Christmas."Reuse content