As I was gathering up my stored parts to install the front shocks on my ‘66, I was checking the part numbers in the ‘66 AIM for the two grommets that are used at the upper end of the front shock absorbers. These two grommets are items 3 and 8 in this sketch from the ‘66 AIM.
IMG_6814.jpg
I have NOS examples of the “upper-upper” grommet (GM 3790341), but the only “lower-upper” grommets I had were ones that came with a set of AC Delco Reactek shocks I bought many years ago. The ‘66 AIM calls out part number 3708378 for the lower-upper grommets. In searching the DB archives there is limited information about grommet 3708378. In 2020, Joe Lucia talked a bit about grommet 3708378 and stated that GM claimed it was used through 1982. In fact, for Corvettes, that same part number appears at least as early as the 1956 AIM and as late as the 1982 AIM. This is in spite of the fact that as Joe reports it was discontinued from service in July of 1966. Which of course does not mean it was discontinued on the production line in 1966. In my Google searches I also found some evidence to suggest that GM 3708378 was used as early as 1949.
So my next questions were, what does GM 3708378 look like and how do my Reactek grommets compare? In searching Goggle images and eBay I was about to find several NOS examples of GM 3708378. Here’s one example I purchased on eBay.
IMG_6813.jpg
Unlike newer GM shock grommets and unlike the Reactek grommets, GM 3708378 does not have a reduced diameter on one side, it is simply a right, circular cylinder with a hole in it.
I don’t believe any of the common Corvette reproduction parts companies sell a comparably configured grommet. But in my Google search I found a company, Steele Rubber Products, who sells a very close reproduction (part # 60-0235-33; $8.29 ea). (As an aside, Steele Rubber says their reproduction is made from “EPDM dense rubber”.) The next image shows an NOS GM 3708378 on the left and the Steel Rubber reproduction on the right.
IMG_6809.jpg
Here are the dimensions for these grommets:
IMG_6815.jpg
The most obvious difference between the NOS GM grommet and the reproduction is the height, where the Steele Rubber grommet is about a tenth of an inch taller. That difference is easy to see with the grommets placed side by side.
IMG_6811.jpg
On a more subjective note, another slight difference between the GM NOS examples I have and the Steele Rubber reproduction is the GM examples seem a bit stiffer. But I only assessed that by pressing down on the grommets as hard as I could by hand. And who know how the stiffness of the GM grommet has changed since it was almost certainly made more than 58 years ago. Maybe the GM grommet started out a bit softer and gas hardened with age.
One question I can’t answer is whether GM 3708378 was indeed used on all Corvettes from 1956 through 1982. I’m assuming it was, but absent finding evidence from Bowtie cars I may never know. My inclination is to believe is was used over those many years since it was called out in the AIM and it never revised to another part number though 1982.
The upshot of my story is that NOS examples of GM 3708378 do occasionally show up on eBay. But a quicker way to procure a reasonable facsimile is by purchasing the Steele Rubber reproduction. I also want to be the first to admit that visualizing the lower-upper grommet once installed is pretty difficult. So the difference in configuration between the simple cylinder grommet vs one with a reduced diameter is unlikely to be seen on the judging field. But for those who want to use a grommet configured like the one GM probably used originally, it’s possible to do that.
Gary
IMG_6814.jpg
I have NOS examples of the “upper-upper” grommet (GM 3790341), but the only “lower-upper” grommets I had were ones that came with a set of AC Delco Reactek shocks I bought many years ago. The ‘66 AIM calls out part number 3708378 for the lower-upper grommets. In searching the DB archives there is limited information about grommet 3708378. In 2020, Joe Lucia talked a bit about grommet 3708378 and stated that GM claimed it was used through 1982. In fact, for Corvettes, that same part number appears at least as early as the 1956 AIM and as late as the 1982 AIM. This is in spite of the fact that as Joe reports it was discontinued from service in July of 1966. Which of course does not mean it was discontinued on the production line in 1966. In my Google searches I also found some evidence to suggest that GM 3708378 was used as early as 1949.
So my next questions were, what does GM 3708378 look like and how do my Reactek grommets compare? In searching Goggle images and eBay I was about to find several NOS examples of GM 3708378. Here’s one example I purchased on eBay.
IMG_6813.jpg
Unlike newer GM shock grommets and unlike the Reactek grommets, GM 3708378 does not have a reduced diameter on one side, it is simply a right, circular cylinder with a hole in it.
I don’t believe any of the common Corvette reproduction parts companies sell a comparably configured grommet. But in my Google search I found a company, Steele Rubber Products, who sells a very close reproduction (part # 60-0235-33; $8.29 ea). (As an aside, Steele Rubber says their reproduction is made from “EPDM dense rubber”.) The next image shows an NOS GM 3708378 on the left and the Steel Rubber reproduction on the right.
IMG_6809.jpg
Here are the dimensions for these grommets:
IMG_6815.jpg
The most obvious difference between the NOS GM grommet and the reproduction is the height, where the Steele Rubber grommet is about a tenth of an inch taller. That difference is easy to see with the grommets placed side by side.
IMG_6811.jpg
On a more subjective note, another slight difference between the GM NOS examples I have and the Steele Rubber reproduction is the GM examples seem a bit stiffer. But I only assessed that by pressing down on the grommets as hard as I could by hand. And who know how the stiffness of the GM grommet has changed since it was almost certainly made more than 58 years ago. Maybe the GM grommet started out a bit softer and gas hardened with age.
One question I can’t answer is whether GM 3708378 was indeed used on all Corvettes from 1956 through 1982. I’m assuming it was, but absent finding evidence from Bowtie cars I may never know. My inclination is to believe is was used over those many years since it was called out in the AIM and it never revised to another part number though 1982.
The upshot of my story is that NOS examples of GM 3708378 do occasionally show up on eBay. But a quicker way to procure a reasonable facsimile is by purchasing the Steele Rubber reproduction. I also want to be the first to admit that visualizing the lower-upper grommet once installed is pretty difficult. So the difference in configuration between the simple cylinder grommet vs one with a reduced diameter is unlikely to be seen on the judging field. But for those who want to use a grommet configured like the one GM probably used originally, it’s possible to do that.
Gary
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