We've discussed the change from "smooth/flat" design to "ribbed" design that took place at all three assembly plants in the spring of 1969. Recently had a reason to look at this deeper and with my usual collection and graphing process I've come up with a possible change over period for the Dearborn plant. To be useful, surveys like this rely on documentation (pictures in this case) and actual completion date for each example.
Here are examples of both styles
The "smooth or flat" style has two short rib one at the lower rear corner in front of the shock tower area and one at the bottom of the panel above the frame rail. Wire loom often blocks the view of the rear one from clear view in pictures or in person.
The "ribbed" panel has two addition ribs for strength and sound deadening placed vertically in the center of the panel as shown
In collecting the data I found the following and offer it here as evidence of when the change took place. Using a group of cars and my findings the results are pretty clear IMHO. Focus is on the 30 period when the change took place. The vast majority of cars used for the survey were unrestored cars
- Completed Mar 11 - 9F16831x - Smooth Panel
- Completed Mar 15 - 9F17187x - Smooth Panel
- Completed Mar 25 - 9F17742x - Smooth Panel
- Completed Mar 25 - 9F48183x - Smooth Panel
- Completed Mar 31 - 9F48158x - Ribbed Panel
- Completed Apr 2 - 9F48188x - Ribbed Panel
- Completed Apr 2 - 9F17968x - Ribbed Panel
- Completed Apr 16 - 9F18298x - Ribbed Panel So we are down to a 5-7 day period. Hope this helps.
If anyone has documentation from a car completed on or between Mar 25 and 31st that may help get this closer
