Working down the list of running changes that took place during 1967 production at San Jose as the title states we look at windshield washer reservoir change from plastic bag to opaque rigid tank.
Like 65 and 66 production started San Jose started out by installing a black plastic washer bag and bracket. Bracket was welded to the drivers side inner fender panel but differs from 65 & 66 in its design and shape. Here are three pictures to illustrate the typical installation
7R106xxxx
7R1627xxxx
7R1648xxxx
Then they changed to the hard plastic opaque reservoir attached to the drivers side inner fender panel with three hex head screws
7R2230xx
And for the record the head markings found on this example. From 7R02S2072xx
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With one of the largest samplings to date the change over point was pretty easy to see once all of the information was inserted into the tables. For all samplings I notate if the car appears to have been restored some time in the past and if there are any indications of possible repair to the area or panels (restored or not restored). Using the actual build date VINs are organized in order and for examples (in this case possibly only 30% of the sampling) those are placed with other similar groups of like sequential numbers) As in the past orphan findings (most often restored cars) are isolated and not included and with this a strong line exposed itself. Perfect - no. Best we currently have to go by IMHO yes.
So in terms of build date according to what I've collected and what has been submitted the range for the change over appears to be between March 29th through April 7th 1967.
Believe it might be down to two days but I have three restored cars built on the 5th through the 7th that create the possibility of the wider range. They each have the bag. Without these three the survey drops the possibility within a two day spread but just being safe at this point.
As for the possibility of both being installed on the line at the same time I believe that jumping back and forth between the welding of a bracket and not welding one on would only cause confusion and there was really no reason to since the unused earlier version/parts could be recycled back through the service parts channels as they did for damaged parts that arrived at the plant and at close out at the end of the production year.