Looking to find out what is the correct differential tag for my 66 350 it was in February 66 #1099 and there 389s
Around the same time as your 66 was likely being built at San Jose there was a change taking place at the rear end plant with the engineering number shown on the tag. From C5 to C6 it appears Notice in the two examples below both with Feb 1966 dates and the new number dated before the earlier number. Suggests IMO that there was a transition period where they were labeled either way. But if you have one made with the same info shown below you should be safely representing what your car likely came with if you don't have any records from your specific car since its from the last week of Feb 1966. Hope this helps
There are a number of earlier longer threads on the subject. I used the words "rearend tag" to find some. One example is posted below that happened to focus on the OP's 6S1097 auto
Drivetrain Tags (https://www.saac.com/forum/index.php?topic=24677.msg183749#msg183749)
(https://www.concoursmustang.com/forum/gallery/21/6-280525180025-210531498.jpeg)
From the patina in the picture, it looks to me like this is all original, except for it looks like it has some white goop between the differential and the housing, and I would only expect them to be using a gasket? I'm certainly no expert, so am I right or wrong?
Roy
Quote from: TA Coupe on May 28, 2025, 06:31:27 PMFrom the patina in the picture, it looks to me like this is all original, except for it looks like it has some white goop between the differential and the housing, and I would only expect them to be using a gasket? I'm certainly no expert, so am I right or wrong?
Roy
Yes originally they used a black gasket. Not unusual to find some home grown fixes on driven Shelbys over the years of course
Looks like someone took a red oxide primer rattle can to the housing and such also. Not sure why they cared but their car - their choices
Quote from: J_Speegle on May 28, 2025, 06:06:24 PMAround the same time as your 66 was likely being built at San Jose there was a change taking place at the rear end plant with the engineering number shown on the tag. From C5 to C6 it appears Notice in the two examples below both with Feb 1966 dates and the new number dated before the earlier number. Suggests IMO that there was a transition period where they were labeled either way. But if you have one made with the same info shown below you should be safely representing what your car likely came with if you don't have any records from your specific car since its from the last week of Feb 1966. Hope this helps
There are a number of earlier longer threads on the subject. I used the words "rearend tag" to find some. One example is posted below that happened to focus on the OP's 6S1097 auto
Drivetrain Tags (https://www.saac.com/forum/index.php?topic=24677.msg183749#msg183749)
(https://www.concoursmustang.com/forum/gallery/21/6-280525180025-210531498.jpeg)
Is there a current source for getting a replacement Diff tag for a '66 GT350? Trying to help a buddy his tag is MIA.
I understand that the photo is not of the original posters' inquiry, but while we're judging the obvious strays from that of the O.E.M.'s effort of what appears to be "tub & tile caulk" and "ugly" paint, I believe the retaining nut is also "incorrect". :)
Scott.
Quote from: pbf777 on June 29, 2026, 11:15:53 AMI understand that the photo is not of the original posters' inquiry, but while we're judging the obvious strays from that of the O.E.M.'s effort of what appears to be "tub & tile caulk" and "ugly" paint, I believe the retaining nut is also "incorrect". :)
Scott.
;D :o
Well, let's add the copper washer under the nut, too.
Quote from: roddster on June 29, 2026, 12:10:06 PMWell, let's add the copper washer under the nut, too.
But, even though your probably right, wouldn't that be under the tag and hence not visible? :-\
Scott.
Quote from: pbf777 on June 29, 2026, 02:43:39 PMBut, even though your probably right, wouldn't that be under the tag and hence not visible? :-\
Scott.
And if the tag is attached to a stud that got a washer, found a lot not present on studs with tags in the early years All of the studs didn't get them every year. Worker's at Sterling plants choice though there were "typical" locations/practices. They are not always consistent in pattern on unrestored examples.
Often, since the washers are so thin and small diameter they are difficult to see especially with road grime on everything
Quote from: J_Speegle on June 29, 2026, 03:14:25 PM. . . . . found a lot not present on studs with tags.
Yes, I'm sure this, like many things that "were" procedurally outlined and "suppose" to be practiced, but just didn't happen; but of the many, and I mean truly "many", 9-inch pigs that I have pulled over the decades, those that actually seemed to have been unmolested, I'd have to say "rarely", and I certainly wouldn't expect, to not find the copper sealing washers in place. And the "tag" isn't a good substitute, therefore I seem to doubt that there was a deliberate intention by the production planers of leaving the copper washer out on the stud with the tag. But of course that doesn't mean it didn't happen. ::)
Perhaps your of a specialty business has caused you to see a greater concentration of unique production runs which contained this specific anomaly and hence your drawing the impression and statement of: "a lot"? :-\
Scott.
Quote from: pbf777 on June 29, 2026, 04:40:12 PMPerhaps your of a specialty business has caused you to see a greater concentration of unique production runs which contained this specific anomaly and hence your drawing the impression and statement of: "a lot"? :-\
No - Specific business so just memory and a decent size collection of pictures of including pictures of details like being discussed. Helps the memory portion of the comment above ;) Do think I could have chosen a better picture to include in this thread. Often readers do get distracted by other details contained in the pictures and the thread takes a turn.
I think a little "wandering" is a good thing! As if only inadvertently, it presents an opportunity for greater sums of talking and learning subject matter on the forum, this that might not have otherwise been made available if one had to open an individual thread just to point out otherwise small nuances and so otherwise wouldn't have been brought to light. :)
But yeah really, "tub & tile caulk"! You should have known the photo was going to go viral! ::)
Scott.
By the time 6S1099 was built, the number would be a "C6ZX" rather than "C5ZX."
Also, more than likely, it was not originally equipped with a Detroit Locker, so the "L" in the 3.89 would not be there.
Here is an example. This particular tag is the original from 6S933.
Quote from: Brant on June 29, 2026, 10:06:37 PM. . . . . it was not originally equipped with a Detroit Locker, so the "L" in the 3.89 would not be there.
The rear differential options for these did not 'ever' include the "Trac-Loc"? :-\
Scott.
P.S. Looks like the "correct" nut in this picture! ::)
Quote from: pbf777 on June 30, 2026, 11:19:08 AMQuote from: Brant on June 29, 2026, 10:06:37 PM. . . . . it was not originally equipped with a Detroit Locker, so the "L" in the 3.89 would not be there.
The rear differential options for these did not 'ever' include the "Trac-Loc"? :-\
Scott.
P.S. Looks like the "correct" nut in this picture! ::)
It was phased out for 66. Another cost cutting issue by SA. If a customer wanted a Trac Loc or a Detroit locker it was to be dealer installed according to factory memos.