'61 differential dates?
Is the case on a 1961 Posi differential dated? If so is it judged? Where would the date be?
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Re: '61 differential dates?
casting date would be right next to the large thin P and the 3789812.Comment
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Re: '61 differential dates?
How can I tell the ratio of a unit by looking at the gears, etc?Comment
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Re: '61 differential dates?
Richard, to me a picture is worth a thousand words, so I will add the pictures of the dates and stamps already spoken of in this thread.
The ratio is determined by the stamped code on the passengers side per the picture "rear axle 006b". This is located at about 11 oclock if looking from front to rear at the rear axle.
You can find a chart of the codes in the Adams book.Comment
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Re: '61 differential dates?
Richard -
Most GM gearsets have the ratio stamped on the O.D. of the ring gear - pinion teeth-ring gear teeth (i.e., 10-37 would be a 3.70); it's also stamped on the rear face of the pinion gear, but you can't see that with the diff assembled.Comment
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Re: '61 differential dates?
Richard,
Attaching a photo of the codes for 61 Corvettes, too many to type out.
You may have to save it and open with a viewer that can magnify it.
KenComment
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Re: '61 differential dates?
Where is it at in the Noland Book? I can't seem to find it. Thanks!!!Comment
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Re: '61 differential dates?
As John mentioned above, MOST GM ring gears and pinion gears have the numbers stamped on them. BUT, MOST ring gear numbers are covered up by the ring gear flange of the differential, so only the numbers on the pinion gear can be seen, as shown below. The 10-37 are the number of teeth on the pinion gear and the ring gear. The 12 55 is the date the gear was machined, Dec 55, which would have gone into a 1956 car (possibly a Jan 56 built car).
Here are examples of Posi and NON-posi case numbers which include the CASTING dates.
This posi case has a casting date of G114 (it's from a pass car) which translates to July 11, 1964.
This non-posi case has a casting date of H279, which translates to Aug 27, 1959 (MOST PROBABLY it was originally installed in an early production 1960 car).
This is the other side of the non-posi case with the STAMPED letters/numbers. It is stamped AB908. The AB is the gear ratio code (this is a auto tranny code for a passenger car) the 908 is the date the rearend was ASSEMBLED which was Sep 8. The year is NOT included in the stamped date because it was already included on the other side in the CASTING date.
By the way, this style rearend center section was built at BOTH the Detroit Gear and Axle plant and the Buffalo (NY) plant. But Corvette rears ONLY came from the Detroit plant.
Just like many other cast iron parts (ie blocks, heads, etc), rearends had casting dates with either one or two digits in the casting number indicating the year. Detroit rearend cases had ONE digit for the year and Buffalo cases had TWO digits for the year. Also, there were two different Posi big Ps on the posi cases. The Detroit cases had a THIN P and the Buffalo cases had a thick P, as seen below. Again, Corvette rears ONLY came from Detroit.
And just for the heck of it, just in case anyone ever runs across one of these, here is a posi rear from a Canadian car (you northern states guys may encounter one some day).
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Re: '61 differential dates?
The rear axle identification chart I mentioned earlier is in the Adam's book on page 393, showing 1061 to 1962 axle codes.Comment
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Re: '61 differential dates?
The posi unit I found doesn't have the same number scheme decribed in the previous posts. On the end of the pinion I can see 3733372-9-37. The only other thing that is visible on the pinion is a white stamped "M46". This same white M46 is stamped on the edge of the ring gear as well. The only other numbers visible are on the carrier, 12 17 9 B and 22159X. What the heck do I have??
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Re: '61 differential dates?
The 3733372 is the part number. The 9-37 is the number of teeth on the pinion gear and ring gear. Thus, 37 divided by 9 is 4.11. That's the gear ratio that you have. The 22159X on the posi unit is the DANA number of the posi (DANA originally made the early posi units for GM). The 12 17 9 B tanslates to Dec 17, 1959 and I believe B is the second shift. A posi built in Dec 1959 would have been in a 1960 car, thus it would be the later, better, more desireable posi unit. But, it is a 4-series posi unit and you can ONLY use 4- and 5-series gears on it. You CANNOT use a 3-series gear on a 4-series carrier. Won't fit in the case.
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Re: '61 differential dates?
Tom: Thanks very much for the info. One last question, what does the M46 stamped in white on the Pion and Ring gear mean?Comment
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Re: '61 differential dates?
I don't recall ever seeing an M along with the numbers such as 44-45-46, etc. But that number 46 was GM's method of indicating pinion depth for setting up a rearend. To be able to interpret those numbers, you have to have the shop manual which has a table in the rearend section and the same type of pinion depth gauge that GM used to set the pinion depth.
Anyway, the 46 is familiar, but not the M.
I never went by the book anyway, because the instructions are for setting up a rear with new gears. When setting up a rear with used gears, or rebuilding a rear with lots of miles on it, the bottom line indicator of getting a proper setup is the tooth contact pattern when finished. And that pattern may or may not be exactly as illustrated in the book!!!
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Re: '61 differential dates?
Is the carrier I described (numbers visible are on the carrier, 12 17 9 B and 22159X) a Series 3 or the correct series 4?Comment
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