As the title states, does anybody know when the transition from the straight-1910 to offset-1911 headlamp fork took place? I've consulted all the regular sources and couldn't find anything that detailed it down to the month.
You might try Leon Parker.
Leon makes cast iron reproductions of the '09-'10 straight forks from original Ford print. That print he has may have the obsolete date on it, that may tell a date.
Excellent suggestion. Thanks much. I've already sent him a note.
Not the authority here, but I suspect you may find this change was not restricted to a particular month...possibly a running transition over a period of months as changeovers involved multiple suppliers and components. I think it probable that Ford exhausted these various parts inventories and completed contract delivery commitments before changes became fully executed. Case in point may be the current discussion regarding 1915 front wheel hubs. I'll be curious to hear your findings.
Did a review of Bruce's CD encyl. and gained some number info.
The forked headlamp brackets are T-3663 (Right) and T-3664 (Left)
T-3663 Part# 1301 ('09-'11) Part# 1301B ('12-'14)
T-3664 Part# 1348 ('09-'11) Part# 1348B ('12-'14)
The part #'s changed to rev B when the brackets were made of drop forged 'E' steel. These are the curved off-set ones.
Bruce says the '1911' cars probably began by Oct. 25, 1910, as that is when the Blue painted ones began, and many parts changed for the '1911 model year'.
Thanks Scott and Dan. My email to Mr. Parker has not yet been answered. When he does, I'll follow-up.
I suspect Scott is right. It would just be interesting to hear what has been found in era photos or people know from solid unrestored cars. To read the Guidelines it strictly breaks it down to model year. At least if it were known when the offset fork came on the scene there would be some sense of when they might have overlapped.
Maybe I'll try to post some early '11 era photos I have saved. One is particular is very good and I've been sitting here staring at a fork against the photo, but it's hard to determine what's what. I believe it also affects the height of the lamp. Gets tricky to tell as lamp diameters and chimneys change with each model.