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Some time ago a member e-mailed me with a question regarding correct universal joints for his mid-year Corvette. It so happened that I was in the process of doing a little research on this subject at the time and, although I provided him the specific information that he sought, I told him that I would post additional information to the board at a later time. Well, that later time is now.
In order to keep the post to a reasonable and acceptable length, I am going to make this a 3 part "series" and limit the scope of the series to the 63-79 model years. The reason for the selection of 3 parts is the fact that there are basically 3 different universal joint applications used in Corvettes during the 63-79 time period. The first is the rear drive half-shafts. The second is driveshaft application for all Corvettes from 1963 to 1967 and manual transmission models from 1968 through 1970. The third application is 1968 to 1970 Corvettes with TurboHydramatic trans and all 1971 to 1979 Corvettes.
To begin with I want to state that all Corvette PRODUCTION universal joints used from 1963 through 1979 are NOT equipped with grease fittings. Also, although the configuration of u-joints of a given part number are the same, markings on the trunnion or bearing caps may vary. I have a large collection of NOS examples of every u-joint ever used on a production Corvette from 1963 to 1979 and I can say with certainty that markings vary within part numbers.
1963-1979 REAR DRIVE HALF-SHAFT UNIVERSAL JOINTS:
1963 thru approximately mid-1965
During this period, Corvettes were equipped with universal joint GM #3851520. This joint used a "cross-type" trunnion with no indentions in the center of the trunnion and no identification markings. The trunnion has a boss for a grease fitting, but it is not drilled and tapped. The bearing cap seals are black rubber. The bearing caps have a slight indented area in the center of the ends and there are no markings whatsoever on the ends. Bearing caps are 1.185" in diameter. I believe that these u-joints were of internal, GM manufacture.
approximately mid-1965 through approximately 12-76
During this period, Corvettes were equipped with universal joint GM #3889696. This universal joint used a "square-type" trunnion. There were no indentions in the center of the trunnion and some examples have an undrilled boss for a grease fitting, while others don't. Some examples have a "dabbed-on" pink dye inspection mark on the corner of the trunnion, some have a "dabbed-on" yellow inspection mark, and some have no inspection mark at all. Some trunnions have a very small Chevrolet "bow-tie" cast into them, the first time that I have ever seen a vintage part with a cast-in "bow-tie" emblem. Other trunnions simply have "GM" cast into them. Most bearing caps have flat, non indented ends. Bearing cap seals are black rubber and bearing caps are 1.185" in diameter. I believe that these u-joints were of internal, GM manufacture.
approximately 1-77 through end of production 1979
During this period, Corvettes were equipped with universal joint GM # 374246. This universal joint used a "cross-type" trunnion without indented center. On the center of the trunnion was cast "Spicer" and various manufacturing marks. There is an undrilled boss for a grease fitting. Bearing caps ends have an indented area with the word "Spicer" either stamped or cast-in. Bearing cap seals are black rubber.
GM #374246 was available in service until September, 1993 when it was replaced by GM #7834387. In July, 1996 the latter part was discontinued and replaced with GM #26049843. This current part uses a "round-type" trunnion manufactured from forged powder-metal. There is a round indention on both sides of the trunnion center, there are no markings indicating manufacturer, and there exists no boss for a grease fitting. Bearing caps are longer than previous u-joints and the ends are indented. The number "55" is stamped on the ends and bearing seals are black rubber. Although totally different in configuration to the originals, I believe these to be a very high quality piece.
I also want to emphasize that although several part numbers have been used over the years, all are functionally equivalent inasmuch as all Corvette half-shafts during the 63-79 period used the same size u-joint.
Part II---All 1963-1967 Driveshaft U-Joints and 1968-1970 With Manual Transmission U-Joints-----To Be Continued Later......................
In order to keep the post to a reasonable and acceptable length, I am going to make this a 3 part "series" and limit the scope of the series to the 63-79 model years. The reason for the selection of 3 parts is the fact that there are basically 3 different universal joint applications used in Corvettes during the 63-79 time period. The first is the rear drive half-shafts. The second is driveshaft application for all Corvettes from 1963 to 1967 and manual transmission models from 1968 through 1970. The third application is 1968 to 1970 Corvettes with TurboHydramatic trans and all 1971 to 1979 Corvettes.
To begin with I want to state that all Corvette PRODUCTION universal joints used from 1963 through 1979 are NOT equipped with grease fittings. Also, although the configuration of u-joints of a given part number are the same, markings on the trunnion or bearing caps may vary. I have a large collection of NOS examples of every u-joint ever used on a production Corvette from 1963 to 1979 and I can say with certainty that markings vary within part numbers.
1963-1979 REAR DRIVE HALF-SHAFT UNIVERSAL JOINTS:
1963 thru approximately mid-1965
During this period, Corvettes were equipped with universal joint GM #3851520. This joint used a "cross-type" trunnion with no indentions in the center of the trunnion and no identification markings. The trunnion has a boss for a grease fitting, but it is not drilled and tapped. The bearing cap seals are black rubber. The bearing caps have a slight indented area in the center of the ends and there are no markings whatsoever on the ends. Bearing caps are 1.185" in diameter. I believe that these u-joints were of internal, GM manufacture.
approximately mid-1965 through approximately 12-76
During this period, Corvettes were equipped with universal joint GM #3889696. This universal joint used a "square-type" trunnion. There were no indentions in the center of the trunnion and some examples have an undrilled boss for a grease fitting, while others don't. Some examples have a "dabbed-on" pink dye inspection mark on the corner of the trunnion, some have a "dabbed-on" yellow inspection mark, and some have no inspection mark at all. Some trunnions have a very small Chevrolet "bow-tie" cast into them, the first time that I have ever seen a vintage part with a cast-in "bow-tie" emblem. Other trunnions simply have "GM" cast into them. Most bearing caps have flat, non indented ends. Bearing cap seals are black rubber and bearing caps are 1.185" in diameter. I believe that these u-joints were of internal, GM manufacture.
approximately 1-77 through end of production 1979
During this period, Corvettes were equipped with universal joint GM # 374246. This universal joint used a "cross-type" trunnion without indented center. On the center of the trunnion was cast "Spicer" and various manufacturing marks. There is an undrilled boss for a grease fitting. Bearing caps ends have an indented area with the word "Spicer" either stamped or cast-in. Bearing cap seals are black rubber.
GM #374246 was available in service until September, 1993 when it was replaced by GM #7834387. In July, 1996 the latter part was discontinued and replaced with GM #26049843. This current part uses a "round-type" trunnion manufactured from forged powder-metal. There is a round indention on both sides of the trunnion center, there are no markings indicating manufacturer, and there exists no boss for a grease fitting. Bearing caps are longer than previous u-joints and the ends are indented. The number "55" is stamped on the ends and bearing seals are black rubber. Although totally different in configuration to the originals, I believe these to be a very high quality piece.
I also want to emphasize that although several part numbers have been used over the years, all are functionally equivalent inasmuch as all Corvette half-shafts during the 63-79 period used the same size u-joint.
Part II---All 1963-1967 Driveshaft U-Joints and 1968-1970 With Manual Transmission U-Joints-----To Be Continued Later......................