1963 motor mounts

[David L.]

Re: 1963 motor mounts

Pictured below is a pair of NOS 3980701 mounts (1970 Corvette and maybe late 1969 Corvette).
GM # 3980701 replaced GM # 3967767 (1969 Corvette mounts) in Oct. 1969 and GM # 3980701 was removed from service in July 1970 as per Chevrolet Parts History (for service parts, not assembly line parts).

Dave

[Joe R.]

Re: 1963 motor mounts

Thru the years I have sold dozens of those. Guess since those had the part numbers on them and were in the GM box people assumed they were NOS but actually NORS parts. Originals did not have the part number.

JR

[David L.]

Re: 1963 motor mounts

Thru the years I have sold dozens of those. Guess since those had the part numbers on them and were in the GM box people assumed they were NOS but actually NORS parts. Originals did not have the part number.

JR

It seems odd to me that the 3980701 mounts were only sold "over the counter" from Oct. 1969 to July 1970 and that theses "over the counter mounts" would have the part number on them but the 3980701 mounts installed on the 1970 assembly line (and possibly at the tail end of the 1969 assembly line) would not the part number on them. Did the factory use two different molds, one for "over the counter" mounts and one for assembly line mounts or were the "over the counter" mounts made in one factory while the assembly line mounts made in a different factory?

According to my notes on Aug. 8, 1989, I had the following engine mounts in my collection that I purchased at swap meets:
1. a used 1963-1965 Corvette engine mount with the number "3796050" number.
2. a pair of 1961-1968 Chevrolet passenger mounts with the number "3777409".
3. a used L1966-1968 Corvette mount with the number "3886488 AU 79".
4. a pair of NOS (or NORS or whatever) L1966-1968 or maybe 1969 Corvette mounts with the numbers "3967767-GREEN" and "3886466-BLACK" on each mount. These would be "over the counter" mounts.

Dave

[Joe L.]

Re: 1963 motor mounts

It seems odd to me that the 3980701 mounts were only sold "over the counter" from Oct. 1969 to July 1970 and that theses "over the counter mounts" would have the part number on them but the 3980701 mounts installed on the 1970 assembly line (and possibly at the tail end of the 1969 assembly line) would not the part number on them. Did the factory use two different molds, one for "over the counter" mounts and one for assembly line mounts or were the "over the counter" mounts made in one factory while the assembly line mounts made in a different factory?

According to my notes on Aug. 8, 1989, I had the following engine mounts in my collection that I purchased at swap meets:
1. a used 1963-1965 Corvette engine mount with the number "3796050" number.
2. a pair of 1961-1968 Chevrolet passenger mounts with the number "3777409".
3. a used L1966-1968 Corvette mount with the number "3886488 AU 79".
4. a pair of NOS (or NORS or whatever) L1966-1968 or maybe 1969 Corvette mounts with the numbers "3967767-GREEN" and "3886466-BLACK" on each mount. These would be "over the counter" mounts.

Dave

Dave------

I HIGHLY doubt that original mounts used in PRODUCTION differed from the same mount sold in SERVICE. I expect that both had part numbers on them. However, the numbers are usually very faint and may be hard to discern on an aged, greasy engine mount that's also had some degree of heat and age induced rubber deterioration over time.

[Joe L.]

Re: 1963 motor mounts

JR,

Here is my answer:

Upper left: Aftermarket mount, # 2249
Upper Right & lower Right: L66-68 Corvette, # 3866466
Lower Left: 1970 Corvette & maybe Late 69 Corvette, #3980701

Dave

Dave-----

The mount on the lower left is not an original GM mount-----it's aftermarket. Note the configuration of the locking bracket versus the configuration of the same bracket in your photo of the NOS GM #3980701. The configuration of the NOS mount evidences the "angled" ends of the bracket. This is characteristic of the 3980701 mount (I have many NOS and they are all like this). Aftermarket usually has the "flat" bracket.

[Joe L.]

Re: 1963 motor mounts

Dave------


A little more info on the locking mounts:

The GM #3980701 was available as a separate part for a short time (until July, 1970). However, thereafter it was available as part of kit GM #3990916. The kit included one GM #3980701 motor mount + one GM #399803 through bolt, one GM #9422299 locking nut, two GM #103342 washers, and an instruction sheet. This kit was available until 1978 when it was replaced by kit GM #6258154.

GM #6258154 was originally released about September, 1972. It contained one motor mount GM #330973 + one GM #399803 through bolt, one GM #9422299 locking nut, two GM #103342 flat washers, and an instruction sheet. The 330973 was never available separately in SERVICE. The 6258154 was finally discontinued without supersession about 8-10 years ago.

Some folks think that the motor mounts for all 1970-82 were the same. They are incorrect.The GM #3980701 motor mount was used in PRODUCTION for 1970-72 Corvettes. The GM #330973 was used in PRODUCTION for 1973-82 Corvettes. While the two mounts are functionally interchangeable, they are not configured exactly the same. The most prominent difference is the configuration of the locking bracket. The 3980701 has a locking bracket with "angled" ends. The 330973 locking bracket has "rolled down" outer edge. In addition, the spacers used on all 3980701 mounts as well as early 330973 mounts were of cast or forged construction. Later examples of the 330973 mounts use a fabricated steel spacer with butted ends. The cast/forged spacers are attached to the frame of the mount with projection or spot welds. The fabricated steel spacers are attached with MIG welds.

Shame on any 1970-72 owner showing up on the judging field with 330973 motor mounts!

[Chester C.]

Re: 1963 motor mounts

I know now what the locking bracket looks like and that 63's did not have that feature but just what is the purpose of a locking bracket.

[David L.]

Re: 1963 motor mounts

Dave------

I HIGHLY doubt that original mounts used in PRODUCTION differed from the same mount sold in SERVICE. I expect that both had part numbers on them. However, the numbers are usually very faint and may be hard to discern on an aged, greasy engine mount that's also had some degree of heat and age induced rubber deterioration over time.

Joe,

I totally agree with you. I never said that assembly line mounts did not have part numbers on them.

Dave

[David L.]

Re: 1963 motor mounts

I know now what the locking bracket looks like and that 63's did not have that feature but just what is the purpose of a locking bracket.

Back in 1967 when I was 20 years old I owned a 1960 Chevrolet convertible w/283 engine that I replaced the A.T. with a 3-speed M.T. with a Hurst Mystery Shifter. When one of the engine mounts failed the engine would lift up a few inches on one side when I accelerated. I had to replace the mounts. Sometime in the 1960's GM had a "quick fix" cable to fasten to the engine mounts so that when the mounts failed the engine would only lift up a little bit. When the locking mounts fail the engine will only lift up a little bit, not a few inches.

Dave

[David L.]

Re: 1963 motor mounts

Joe,

I bought my 1966 Corvette convertible in 1979 and drove it for about one year before I started to what turned out to be a 16 year restoration. The 4-speed transmission was original but the engine was not. The mounts that I removed were the 330973 mounts. I assume that the engine mounting bolts are GM # 399803 bolts as they are 7/16"-14 X 4 7/16" with the "R", "S", and "C" marking on the heads.

Thanks for the info about the 1970-1972 3980701 mounts.

Dave

[Joe L.]

Re: 1963 motor mounts

Joe,

I totally agree with you. I never said that assembly line mounts did not have part numbers on them.

Dave

Dave------


I realize that. I was simply agreeing with your opinion that the PRODUCTION and SERVICE mounts were not different.