Mystery bolt to ID and potentially up for adoption

[Gary B.]

Can anyone identify the bolt in these images?


D1805D5A-B79E-4D48-92A2-A8ABADBA5762.jpg

5C7576AF-137D-4ED6-925C-3A766DC0A8E9.jpg


It’s a Gr 8, TR headmark bolt, with 7/16-20 threads x 1 3/4” long. I’m guessing it was zinc or cad plated, but the plating is no longer intact or obvious. Initially I assumed it came off my ‘66 or I had acquired it to replace an equivalent bolt from my ‘66 that was rusty. But after consulting with several knowledgeable bolt people, no one has been able to ID it.


I do know some similar bolts on a ‘66 that it is not. It is not any of the three 7/16-20 Gr 8 bolts that attach the steering damper to its RH bracket, or that attach that bracket to the relay rod. Those 3 bolts are either longer or shorter. Nor is it the 7/16-20 (I think) bolt that attaches the steering knuckles to the front spindles. Those steering knuckle bolts are longer.


But a TR headmark bolt is period correct for the 60s. But maybe for some year other than my ‘66. Can anyone ID this bolt? If that identification confirms that it doesn’t go anywhere on my ‘66 that I’m currently lacking, I’m happy to mail the bolt to anyone who wants it. On my dime. I’m loathe to throw away a vintage bolt that might be desired for someone else’s restoration.


Thanks,


Gary

[Mark F.]

Re: Mystery bolt to ID and potentially up for adoption

Gary,

it's been 15+ years since I tore my calipers apart, but IIRC the finer threads look like the bolts that hold the two caliper halves together...(?)

Mine are grade 8, but don't have the TR in the center...

Might that be what you have there?

P9180008.jpg

[Gary B.]

[Michael G.]

Re: Mystery bolt to ID and potentially up for adoption

Front lower control arm?

[Gary B.]

[Edward J.]

Re: Mystery bolt to ID and potentially up for adoption

Gary, I think the steering arm had 7/16 fine thread bolts they were grade 8, the steering arm bolts had two different Length bolts I believe.

[Gary B.]

[Michael G.]

[Gary B.]

[Gary B.]

Re: Mystery bolt to ID and potentially up for adoption

LIC used to see a repro of the front, lower A-arm to frame bolts, but they were an LE headmark, which I don’t believe is correct for C2. Paragon sells a TR repro, in zinc, and it says it’s 7/16-20 x 1 1/2”. I think a 1 1/2 “ long bolt would not quite completely emerge from the nut plate. So, I don’t know if the 1 1/2” length is the same length as the GM original.

Gary

PS. I just found a 1963 GM parts book online and it lists GM 454976 as 7/16-20 x 1 3/4, 300M. Suggesting the Paragon repro is 1/4” short.

[Michael G.]

[Gary B.]

Re: Mystery bolt to ID and potentially up for adoption

Michael,

Fortunately, this one was an extra in my stash.

It turns out there is still a minor mystery about that bolt. In the 63-65 AIM#0s the GM part number is 454976, which I can find in GM parts books. In the 66 and 67 AIMs, the part number is 454975. Which I can find no description via a Google search. In the 66 AIM, the revision notes start at #9, so the first 8 revision notes are gone. So, is GM 454975 a real #? Or was it a typo when the ‘66 AIM was created, which propagated to the ‘67 AIM?

Gary

[David B.]

Re: Mystery bolt to ID and potentially up for adoption

454976 7/16-20 x 1 3/4 zinc 300-M class 2A thread
454975 7/16-20 x 1 5/8 zinc 300-M class 2A thread both hex head

[Gary B.]

Re: Mystery bolt to ID and potentially up for adoption

Thanks David. That completely solves the mystery. Undoubtedly, the 66-67 bolt was 1/8” shorter to save a fraction of a penny per bolt. Times many tens of thousands. I have to think the 454975 bolt was never sold in service and that’s why it doesn’t show up in a Google search.

I suspect I have the 63-65 1 3/4” long bolts on my car. But I’m going to say GM was still using up ‘65 inventory when my ‘66 was built.

Gary

[Ronald L.]

Re: Mystery bolt to ID and potentially up for adoption

Someone has the GM standard parts book!