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Several weeks ago there was a discussion on the board regarding the configuration of the engine-mounted clutch cross shaft stud and its seal. I've done a little research on this one and I think that I have some interesting information to report. First, though, and considering my disdain for discussions of trivialities, my apologies for resuming discussion on a rather "esoteric" subject.
First, the easy part: the engine mounted ball stud specified for use in PRODUCTION for every Corvette from 1963 to 1981 was GM #3752863. This is confirmed by reference to the various AIMs and other documents. The GM #3752863 ball stud incorporated a FELT dust seal of GM #3743355.
Now, the not-so-easy part: for SERVICE, the ball studs specified were somewhat different. For 1963-64, the SERVICE ball stud specified by GM was GM #3816340. I do not know the configuration of this ball stud. Beginning in about 1965, the GM #3816340 ball stud was replaced by GM #3866568. This ball stud remained the SERVICE ball stud for all 1963-72 model Corvettes for many years continuing right up to the present time. I'll describe it later.
Beginning about 1973, the GM #3752863 became the SERVICE ball stud for 73+ model Corvettes and was ultimately specified for all 73-81 Corvettes. Keep in mind that this is the same ball stud that was specified for use in PRODUCTION for ALL 1963-81 Corvettes, but was NEVER specified as the SERVICE ball stud for 63-72 Corvettes.
Within the past several months, the GM #3752863 ball stud was discontinued from SERVICE and replaced by the GM #3866568. So, now, the GM #3866568 ball stud is the SERVICE ball stud for all 1963-81 Corvettes. As far as I can tell, though, the 3866568 ball stud was never used in PRODUCTION-----at least it was never specified for use in PRODUCTION on Corvettes.
How do the GM #3752863 and GM #3866568 differ? Well, they are the same in all functional dimensions----the overall length, the length of the threaded portion, the thread size of the threaded portion, and the OD of the ball which articulates with the bellcrank. So, they are interchangeable. The differences involve the configuration of the shaft portion between the ball and the flange, the configuration of the flange, and the seal material. The seal is high-density, black foam rubber rather than the felt used on the 3752863. So, now we know how these rubber seals got into the mix of things.
One other curious difference that I noted regarding the shaft portion of the ball studs is that the 3866568 has a very thin, lightly cut annular groove around the shank whereas the 3752863 does not. I don't know the purpose of this groove. Otherwise, the shank portion of the 2 ball studs are shaped slightly differently, but it's impossible to describe that difference since it's very subtle.
Since the 63-81 PRODUCTION ball stud, GM #3752863, was available in SERVICE since 1963 (I confirmed that, too), why did GM not specify it as the SERVICE ball stud for 1963-72 Corvette applications? I don't know the answer. Was the GM #3866568 ball stud ever used in PRODUCTION, even though I can find no record of it? Unfortunately, I don't know the answer to that, either. However, I know the ball stud on my car to be original so, when I get a chance, I'm going to inspect it for the presence or absence of the lightly cut annular groove. And, I'll compare it to NOS known examples of the 3752863 and 3866568 which I have.
First, the easy part: the engine mounted ball stud specified for use in PRODUCTION for every Corvette from 1963 to 1981 was GM #3752863. This is confirmed by reference to the various AIMs and other documents. The GM #3752863 ball stud incorporated a FELT dust seal of GM #3743355.
Now, the not-so-easy part: for SERVICE, the ball studs specified were somewhat different. For 1963-64, the SERVICE ball stud specified by GM was GM #3816340. I do not know the configuration of this ball stud. Beginning in about 1965, the GM #3816340 ball stud was replaced by GM #3866568. This ball stud remained the SERVICE ball stud for all 1963-72 model Corvettes for many years continuing right up to the present time. I'll describe it later.
Beginning about 1973, the GM #3752863 became the SERVICE ball stud for 73+ model Corvettes and was ultimately specified for all 73-81 Corvettes. Keep in mind that this is the same ball stud that was specified for use in PRODUCTION for ALL 1963-81 Corvettes, but was NEVER specified as the SERVICE ball stud for 63-72 Corvettes.
Within the past several months, the GM #3752863 ball stud was discontinued from SERVICE and replaced by the GM #3866568. So, now, the GM #3866568 ball stud is the SERVICE ball stud for all 1963-81 Corvettes. As far as I can tell, though, the 3866568 ball stud was never used in PRODUCTION-----at least it was never specified for use in PRODUCTION on Corvettes.
How do the GM #3752863 and GM #3866568 differ? Well, they are the same in all functional dimensions----the overall length, the length of the threaded portion, the thread size of the threaded portion, and the OD of the ball which articulates with the bellcrank. So, they are interchangeable. The differences involve the configuration of the shaft portion between the ball and the flange, the configuration of the flange, and the seal material. The seal is high-density, black foam rubber rather than the felt used on the 3752863. So, now we know how these rubber seals got into the mix of things.
One other curious difference that I noted regarding the shaft portion of the ball studs is that the 3866568 has a very thin, lightly cut annular groove around the shank whereas the 3752863 does not. I don't know the purpose of this groove. Otherwise, the shank portion of the 2 ball studs are shaped slightly differently, but it's impossible to describe that difference since it's very subtle.
Since the 63-81 PRODUCTION ball stud, GM #3752863, was available in SERVICE since 1963 (I confirmed that, too), why did GM not specify it as the SERVICE ball stud for 1963-72 Corvette applications? I don't know the answer. Was the GM #3866568 ball stud ever used in PRODUCTION, even though I can find no record of it? Unfortunately, I don't know the answer to that, either. However, I know the ball stud on my car to be original so, when I get a chance, I'm going to inspect it for the presence or absence of the lightly cut annular groove. And, I'll compare it to NOS known examples of the 3752863 and 3866568 which I have.
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