Dennis:

I am back to thinking that this is a linkage problem. The gears should not control the legnth of the arc that the wipers eventually travel through. If the gears were actually slipping, then an wipers would travel through an arc of the same length but the arc would rotate about the wiper shaft. My wipers traveled too far in both directions before they started jamming.

Although the shaft nuts were tightened and the linkages were checked for looseness, the entire mechanism was not observed while operating. When time allows I will wet the windshield with a garden hose and take a look under the dash with the wipers on. If the cause of slop isn't obvious, then the whole mechanism is coming out for closer inspection.

Note to self -- add a small bottle of Rain-X to the list of things needed before going on a long trip in a 40 year old vehicle. My kid calls the car "Fear Factor". Did your parents regularly drive a 1923 whatever at 70 MPH?

Best regards,

Joe M