The incident, which took place at around 11.50am on Friday, involved a 78-year-old man who came to a stop while driving his blue Seat Ibiza northbound near junction two.
A white Mercedes Citan van driven by a 38-year-old man crashed into the back of the Ibiza when it stopped.
The Ibiza driver was taken to the Queen Elizabeth University Hospital in Glasgow and died on Saturday from what was believed to be an unrelated condition.
The Mercedes driver was taken to Glasgow Royal Infirmary with minor injuries following the crash but was later released.
Police closed the road for a short period of time to investigate the crash.
Officers have appealed to drivers who may have witnessed the collision to come forward.
Sergeant Mark McGowan said on Saturday: “It is important that we can establish exactly what happened here and we are appealing for anyone who may have seen either vehicle involved before the incident took place to get in touch.
“We would also ask anyone who was driving in this area yesterday before midday who has dash-cam footage to get in touch with us. You may have information that can help.”