Police were called to the incident between Greenfield and Holmfirth shortly after 4:30pm, and found a red Ford Mondeo and a Jeep Commander partly blocking the road after a collision.
A Greater Manchester Police spokesman said there were no reports of any injuries, but there was some debris spread around the carriageway. Officers from West Yorkshire Police assisted GMP at the scene.
The smash happened about 400 yards from the district boundary with Kirklees, near the bends before the long straight stretch. It was very close to the spot where off-duty policeman Graham Lyne was knocked off his motorbike and killed last month.
Figures obtained last year by Saddleworth News under Freedom of Information laws showed that the A635 between the Clarence roundabout and the boundary was the second-most dangerous road in Saddleworth, with a total of 45 accidents between 2000 and 2009 in which at least one person was injured. Only the A62, with 75 incidents, had more.
However, there were just two such crashes on the A635 in 2010, in keeping with the overall decline in the number of road accidents in Saddleworth in recent years.
Oldham Council recently announced in the Oldham Chronicle that it would be introducing a 50mph limit on the road, in response to safety concerns. You can read that article here.