1967 - Bolt Identification (5/16-18 x 7/8") (Grade 5, "C" headmark)

[Scott S.]

This bolt (pictures below) was in one of my "Seat Track to Floor bolts" bags (should be UPC 1Seats-J5, Item 9, GM 3847757). There should be eight bolts total (four per seat). Seven of them measure 5/16-18 x 7/8" long, six are "E" headmark Gr5 bolts, plus this Gr5 bolt (same dimensions) headmarked "C". All are indented hex bolts with att/flat washer (sems), pointed tip.

The eighth bolt (not shown) is different and appears to be incorrect, indented hex Gr2 with "E" headmark, flat tip, measuring 5/16-18 x 3/4" long, flat washer is not attached.

Is this 5/16-18 x 7/8" bolt (below) with "C" headmark and three lines (Grade 5) a correct headmark seat-track-to-floor bolt for 1967?

[Gene M.]

Re: 1967 - Bolt Identification (5/16-18 x 7/8&quot (Grade 5, "C" headmark)

Yes, It is one of many seen on mid years. The "E", "RBW" and others are used as well. I don't think GM cared who's brand they pulled out of the tray.

Typical mftg practice does not seperate them in use. All different mftg bolts of the same p/n are mixed.

[Peter H.]

Re: 1967 - Bolt Identification (5/16-18 x 7/8&quot (Grade 5, "C" headmark)

I Have Used The Bolts With The C On Them To Fasten The Hood Latch To The Firewall .

[Scott S.]

Re: 1967 - Bolt Identification (5/16-18 x 7/8&quot (Grade 5, "C" headmark)

Yes, It is one of many seen on mid years. The "E", "RBW" and others are used as well. I don't think GM cared who's brand they pulled out of the tray.

Typical mftg practice does not seperate them in use. All different mftg bolts of the same p/n are mixed.

I Have Used The Bolts With The C On Them To Fasten The Hood Latch To The Firewall .

Thanks for the replies Gene and Peter. They sort of open up a related can of worms. There are several posts in the archives indicating that the seat bolts changed throughout 1963-1967, but the accounts differ, so I looked up the seat bolts ("Screw Asm.") with each year's AIM below:

1963: all the same - Section 1, Sheet D4, Item 3, GM 3795514 Screw Asm. (all, front AND rear seat brackets)
1964: all the same - 1Seats, Sheet 4, Item 3, GM 3847758 Screw Asm. (all, front AND rear seat brackets)
1965: half and half - 1Seats-J4, Item 3, GM 3847758 Screw Asm. (rear seat bracket bolts only) ------- 1Seats-J4, Item 7, GM 3847757 Screw Asm. (front seat bracket bolts only)
1966: all the same - 1Seats-J5, Item 7, GM 3847757 Screw Asm. (all, front AND rear)
1967: all the same - 1Seats-J5, Item 9, GM 3847757 Screw Asm. (x8, all, front AND rear, 4 per seat)


I have found official documentation for "GM 3847758, Screw Asm." For 1967 (and probably other years) this bolt (Screw Asm.) is used in many places, including the steering assembly, UPC 9-A4, Item 9 (see below, Adobe PDF attachment, item 9). I have this particular Screw Asm. from the steering column here with me, it measures 5/16-18 x 1-1/16" (indented hex, Grade 5, "E" headmark, pointed tip, captive washer).

I found this same drawing from the 1967 AIM pictured in another GM publication dated October 1, 1967 which shows the dimensions of the bolt used in this same application, specifically referencing 1967-1968 steering columns, and calling out the exact same measurements as the Screw Asm. from my steering column, 5/16-18 x 1-1/16" (see Jpeg picture below, item 9, same item number as in the assembly manual). That would seem to nail down the characteristics of GM 3847758 as fairly certain.


So far, I have not found any official GM source stating the dimensions for GM 3847757 Screw Asm. I have read conflicting information in the archives that they have pointed tips, and that they have flat tips; they measure 5/16-18 x 3/4" and 5/16-18 x 7/8"; they have serrated captive washers, and they have plain captive flat washers.

One of my eight seat bolts is obviously incorrect, having a flat tip but no grade marks and no captive washer. The remaining 7 of my seat-track-to-floor bolts (1Seats-J5, Item 9, GM 3847757) are Grade 5 indented hex bolts with pointed tips, measured carefully several times at 5/16-18 x 7/8" long. A couple were 27/32" long, just shy of 7/8" long, but that is due to inconsistencies with the formation of the pointed tip. They were all noticeably longer than 3/4". Six have the "E" headmark and one has the "C" headmark, otherwise identical.

It appears to be undisputed that GM 3847757 is an indented hex, Grade 5 bolt with attached washer. The question seems to be about the Length, the Captive Washer (serrated or plain) and what ought to be the most obvious distinction, whether it has a Pointed Tip or a Flat Tip.

Does anyone have information, official GM documentation or otherwise, to set the record straight on GM 3847757 Screw Asm.?

[Ronald L.]

Re: 1967 - Bolt Identification (5/16-18 x 7/8&quot (Grade 5, "C" headmark)

Scott,

From a famous 66 survivor car seen at the 2011 Novi National Convention, as well as another not so famous survivor 66 car that has the exact same configuration on bolts that have NEVER been removed from the car...

3847758 was a blunt tip screw circles in the head mark.

For 1966 (even though the asy sheet UPC 1 J5 was changed in 1965) they used this screw on the inboard seat bracket - both sides.



Interestingly enough the outboard screws were a E head mark dog point 3847757 as is shown in the AIM.

It seems from 64 on this usage flip flopped if you look at the threads on this topic and its logical this had to do with assembly difficulties in that area.

Now what you may find is a trend by year that the screw changed suppliers, but you won't find all suppliers head marks in a given year such as 1966.

Sourcing to suppliers just did not work that way.

And, and we know, if you look at other areas where this screw is used on the car, these two survivors had E's in all those places.

[Rich P.]

Re: 1967 - Bolt Identification (5/16-18 x 7/8&quot (Grade 5, "C" headmark)

The 2 bolts your talking about could have been used on no less than a dozen places on a mid year. Flat tip, pointed tip, 1/2", 3/4" and 7/8". All recessed head with captured conical washer. All were black phosphate.

[Ronald L.]

Re: 1967 - Bolt Identification (5/16-18 x 7/8&quot (Grade 5, "C" headmark)

By model year quarter a purchasing employee would not be sourcing and requiring a supplier to deliver two completely different parts for the same application under the same part number - the systems don't work that way.

Yes the plant could substitute in an emergency, but haphazzard material control was not the norm.

The norm "here" is many of these cars were restored 30 years ago, and then again 15 years ago and got all sorts of other parts mixed in, especially when you consider what you can find on the web about the various companies supplying screws to these two part numbers.

[Scott S.]

Re: 1967 - Bolt Identification (5/16-18 x 7/8&quot (Grade 5, "C" headmark)

By model year quarter a purchasing employee would not be sourcing and requiring a supplier to deliver two completely different parts for the same application under the same part number - the systems don't work that way.

Yes the plant could substitute in an emergency, but haphazzard material control was not the norm.

The norm "here" is many of these cars were restored 30 years ago, and then again 15 years ago and got all sorts of other parts mixed in, especially when you consider what you can find on the web about the various companies supplying screws to these two part numbers.

Ron,

From researching these bolts previously, they are all indented hex grade 5, all black phos, mostly the same headmark ("E"), all 5/16-18 thread, all (but one) having a pinch-point, it seems that because these bolts were so similar, they were used interchangeably. Not like an emergency substitution, more like it was a "generic" bolt size with multiple applications, so they used whatever was closest at hand. You can't easily tell these bolts apart, unless you stand them up on their heads next to each other, to notice a 1/16" or 1/8" difference in length from bolt to bolt, and the places where they are used don't require that kind of precision length. Any of them will do, and it seems this particular bolt was used in that way.

What you say about many of these cars being restored over the years (sometimes more than once) is certainly true, but the car I'm working on has been in the family since 1976 and was in storage from 1993 until 2008 when we began the restoration. It had not ever been restored previously. This evening I will get my notes and list what was found for each location of these bolts. It was very consistent, the only surprise was the one bolt on the seat tracks.

[Scott S.]

Re: 1967 - Bolt Identification (5/16-18 x 7/8&quot (Grade 5, "C" headmark)

Scott,

From a famous 66 survivor car seen at the 2011 Novi National Convention, as well as another not so famous survivor 66 car that has the exact same configuration on bolts that have NEVER been removed from the car...

3847758 was a blunt tip screw circles in the head mark.

For 1966 (even though the asy sheet UPC 1 J5 was changed in 1965) they used this screw on the inboard seat bracket - both sides.

Ron,

Sorry for the delay, this took a little longer than I anticipated...

I understand that the 1966 cars you examined had bolts like you say, I can only report on the 3847758 bolts used on my ’67. They are all pinch-point bolts at the locations called out in the 1967 AIM.

1BoltWeld-A12, Item 10, 3847758 - pinch point
Both RH and LH sides of the cowl, can be seen from the back side through a hole in the birdcage up under the dash (see pictures below). AIM shows four, I can only see two of them (the uppers) clearly. Indented hex, grade 5, “E” headmark (both). Unsure of length, haven’t tried to remove them. I posted pictures of them a while back when I was trying to figure out where these were found in the AIM, checked them again today to be sure of the tips.

~~~~~~~~~~~~

I spent a few hours one afternoon removing and checking all the bolts I could reach on 1ASM-D2 a few months ago, and wrote all of my findings on a copy of the AIM page that I brought with me for that purpose. The 1966 and 1967 AIM pages are identical for this page. This is what I found:

Item 1, 3855554 Screw Asm: couldn’t see it or reach it, it was up under the dash

Item 4, 3847758 Screw Asm. - pinch point, but wrong bolt (factory substitution)
Indented hex with attached CFW, black phos, grade 5. However, this was an assembly line substitution for 3847758, which I noticed because:
A) at 5/8” diameter, the attached CFW was too small
B) it had “ELH” inside 4 circles for the headmark, which I had not ever seen for any GM 3847758 bolt, but which I had recently discovered at the 1967-only hood-catch to cowl bolts location (11-13-B5, Item 5, GM 3860518). Measures 5/16-18 x 7/8”. Similar to 3847758 except for the size of the attached CFW and being too short. All six of my hood-catch to firewall bolts are identical to this one.

On a related note, Item 6, 3846202 Screw Asm, another very similar bolt, was another Assembly line substitution on this car, again using the same “ELH” grade 5 hood-catch bolt (pinch-point) as was substituted for Item 4 described immediately above.

~~~~~~~~~~~~~~

1Doors-K6, Item 5, 3847758 Screw & Washer Asm. (x8) - pinch point
All eight are the same, grade 5 indented hex black phos bolts with attached 3/4” CFW, “E” headmark. 1/2” ATF. 5/16-18 x 1-1/16”.

~~~~~~~~~~~~~~~

9-A4, Item 9, 3847758 Screw Asm. - pinch point
Indented hex, grade 5, “E” headmark, 3/4” attached CFW, 1/2” ATF. This is the bolt shown in the 1968 Illustrated Parts Book, page is titled “1967-68 Corvette Steering Column and Support (Typical)” that I attached in Post #4 above. The 1968 IPB (October ’67 printing) says the Item 9 bolt (same Item number as the AIM page, and pictured being used at the exact same location as the call out in the AIM) measures 5/16-18 x 1-1/16”. That’s what mine measured.

~~~~~~~~~~~~~~~~~

11-13-A2, Item 4, 3847758 Screw Asm. - pinch point
These bolts (eight of them) hold the small underbody splash shields to the bottom of the inner fender/body. In my case it also secured the Battery Access Panel at the bottom (C60 car). Same bolt used at this location since 1964. All of mine are grade 5, indented hex pinch-point bolts, “E” headmark, all 1-1/16” long.

~~~~~~~~~~~~~~~

11-13-B6, Item 7, 3847758 Screw Asm - pinch point
All four hood hinge-to-body bolts are the same, “E” headmark, grade 5, black phos, indented hex with attached 3/4” CFW, 5/16-18 x 1-1/16”. 1/2” ATF.


To the best of my knowledge, that is every usage for the GM 3847758 on the 1967 model year Corvette. On this particular car, excluding the hood-catch to firewall assembly line substitution bolt found under the dash, every GM 3847758 example was the same: pinch-point, grade 5, indented hex, “E” headmark, black phos, measuring 5/16-18 x 1-1/16”.




I will try to post what I've found for the other bolt you referenced (3847757) tomorrow.


That’s all I have for tonight


Picture #1: 1BoltWeld-A12, Item 10, 3847758, RH upper, front side (front clip removed, looking down into the cowl area)
Picture #2: 1BoltWeld-A12, Item 10, 3847758, back side, RH upper, back side (pinch point)

[Ronald L.]

Re: 1967 - Bolt Identification (5/16-18 x 7/8&quot (Grade 5, "C" headmark)

The 66 AIM can't be the same as 67.

The MY started out with the bolt 757 being used and was changed in 65 and then on 1-16-6...but the plant did not implement the change.


if the x757 part is the blunt tip and is ONLY found in 66 on the inboard attachments then the AIM is basically flipped.

The dog points were on the out board attachments and the same head mark as the column screw, etc.