1966 Differential Cover Dates. Post what you have!

[Chuck B.]

[Mike B.]

Re: 1966 Differential Cover Dates. Post what you have!

Thanks for your post Chuck. Perfect for this thread!

[Mark M.]

Re: 1966 Differential Cover Dates. Post what you have!

Hi Mike,
The lower picture of the AZ rear end cover you posted shows the pattern # on it. GM 1 * That's interest to see the 7 missing as I have a same 375 cover here with the same pattern # but the 7 is there. John Hinckley in his article " Know The Code " said the patterns were made of cast iron or stainless steel. Tag characters for dates, casting numbers and pattern numbers were brass and soldered on to the plates which were fastened with solder, pins or screws to a pattern. That missing 7 has me guessing it got knocked off? The 5 in that picture seems to be crooked! The 375 cover was used a long time, 65-77. I have a number of rear ends and covers which I'll check when I can. There's at least one 66 big block there. Gives me a reason to clean up an old mess.

[Mike B.]

Re: 1966 Differential Cover Dates. Post what you have!

Good Evening Mark,

Thanks for the clarification about where the pattern number is. For some reason I thought you were referring to a number on the housing vs. the cover plate. Schooled again! I also thought that all covers had GM 1 cast into them. Now I know that this is the cover plate pattern number that could have various GM XX numbers cast at the foundry. I just viewed various numbers on 3871375 cover plates for sale online.

Please let me know what you find on that '66 HD differential you have. I'm still looking to match up a nice unit with my car. I need an "AU" 3.36 coded HD posi unit for a December 1st, 1965 built L36 car.

Take care,
Mike

Hi Mike,
The lower picture of the AZ rear end cover you posted shows the pattern # on it. GM 1 * That's interest to see the 7 missing as I have a same 375 cover here with the same pattern # but the 7 is there. John Hinckley in his article " Know The Code " said the patterns were made of cast iron or stainless steel. Tag characters for dates, casting numbers and pattern numbers were brass and soldered on to the plates which were fastened with solder, pins or screws to a pattern. That missing 7 has me guessing it got knocked off? The 5 in that picture seems to be crooked! The 375 cover was used a long time, 65-77. I have a number of rear ends and covers which I'll check when I can. There's at least one 66 big block there. Gives me a reason to clean up an old mess.

Closeup Cover.jpg

[Larry E.]

Re: 1966 Differential Cover Dates. Post what you have!

FWIW: Here is a picture of my 66 L72 Rear Suspension. We can see that there are dates on the Differential but I
do not have the exact dates in front of me. Car is stored now so can not look. Car is a Late June Build St. Louis Body.
Also picture of the upper ratio stamp. Note: Mine has the Julian Stamp Code. Yes I know the thinking was that Julian
Stamp Code did not start till later.(Around 1970 or so) BUT my ratio is FC (4:56) and all the pictures(Not Many) I have of this
ratio ALL HAVE JULIAN DATES. See Below> Please prove me wrong and show me a non-julian dated FC Coded C2.
Thanks in advance>Larry

[Mike B.]

Re: 1966 Differential Cover Dates. Post what you have!

Hey Guys - Just crawled under my 66 L72, late June 66 build[ATTACH=CONFIG]115945[/ATTACH], and the rear cover shows no raised date codes at all.
Uh, disregard the big Yellow Paint Blob, done by the PO when they did a body-off back in the early 90s.
[ATTACH=CONFIG]115944[/ATTACH]

Hi Mike,

Just realizes how close your differential dates are to the example I've posted photos of already in this thread. Figured you may like to see more shots of this '66 HD "AZ" 3.55 posi unit. This is the one with the missing "7" in it's "38713 5" cover plate casting number. See post #30 & #34. I've got more clear shots of this unit & it's connecting hardware if anyone's interested in more photos. It's difficult to make it out from the sharp angle there at the posi lube tag, but I think this cover has no date either.

I grabbed these pics a few years ago from an eBay listing. It's not often that I run across what I feel is an all original example advertised by a seller who knows how to take clear shots of what they're selling. Hats off to this guy.

Enjoy,
Mike
June '66 HD 3.55 Posi (1).jpgJune '66 HD 3.55 Posi (2).jpgJune '66 HD 3.55 Posi (3).jpgJune '66 HD 3.55 Posi (4).jpg

[Wayne G.]

Re: 1966 Differential Cover Dates. Post what you have!

AA3DB721-81FD-43FB-8668-3000A28382B8.jpg

[Mike B.]

Re: 1966 Differential Cover Dates. Post what you have!

Wayne to the rescue!

Thanks for moving this thread back up again. Excellent photo of your '66 cover. It shows everything I'll need when shopping for a correct replacement for my '66. So far I've got 2 excellent reference shots of undated covers from 2 very close cousins of my car. My buddy Ric's '66 HD posi cover is shown in black paint in post #1. His car's (L36) build date is December 7th while yours (L72) is December 9th. My car's (L36) build date is December 1st so as of now I'll assume I need an undated cover.

Anyone who can provide a post here of whether your '66 posi cover is dated or not would be very much appreciated. Small block or big block cars makes no difference. Your response about original cover info will surely help our knowledge of '66 differential ID markings.

Mike



[QUOTE
=Wayne Gibson (7421);929735][ATTACH=CONFIG]116087[/ATTACH][/QUOTE]