Rear spring outer bolts/castle nut

[Rich C.]

Re: Rear spring outer bolts/castle nut

One thing is for sure, you don't want to have one break!!! I had the right one go, VERY LOUD BANG, SCARY!!! It allowed the spring end to dig into the pavement, which in turn twisted the leaf spring. Frame bumper did it's job and kept tire travel from tearing up wheelwell! Luckily I was 100 feet from my driveway.

[Don L.]

Re: Rear spring outer bolts/castle nut

I bought several pair about 15 years ago that I still have - necked-down shanks, 14 threads, Grade 8 (six radial lines), "C" headmarks, black phosphate; photos below.

John, is it possible that the bolts in your photo are reproduction? Reason I ask is that my original bolts (currently in the car) are grade 7 (5 marks) and a comparatively larger "C" than the reproduction bolts that I just bought from Paragon. The Paragon bolts have the same 6 marks as the ones in your photo and the smaller "C" as shown as well in your photo. The bolts I got from Paragon look EXACTLY like yours.

My quandary now is; should I use the reproduction bolts that do not appear to be grade 7, or should I use what might be an original but tired grade 7 bolt?

[Ronald L.]

Re: Rear spring outer bolts/castle nut

Don,

I don't think so, in addition to the data I posted above, I later found a box of these in GM wrappers, C six bars. I bet its a 90's thing.

[Russ S.]

Re: Rear spring outer bolts/castle nut

Like this ? So I guess the center number "92" is not the year of production. From a box of suspension bolts I got off eBay.

The original bolts from my 66 are the Rockford 92 with the five lines.

[Joe L.]

Re: Rear spring outer bolts/castle nut

The original bolts from my 66 are the Rockford 92 with the five lines.

Russ------

There's no way those bolts were originally installed on a 1966 Corvette. Those bolts are GM #351592 and they did not even exist until mid-1974.

[Patrick H.]

Re: Rear spring outer bolts/castle nut

John, is it possible that the bolts in your photo are reproduction? Reason I ask is that my original bolts (currently in the car) are grade 7 (5 marks) and a comparatively larger "C" than the reproduction bolts that I just bought from Paragon. The Paragon bolts have the same 6 marks as the ones in your photo and the smaller "C" as shown as well in your photo. The bolts I got from Paragon look EXACTLY like yours.

My quandary now is; should I use the reproduction bolts that do not appear to be grade 7, or should I use what might be an original but tired grade 7 bolt?

Use a new one, and as a judge I would expect it to be black.

The odds of me seeing the head mark are quite small. If everything else looks correct, the odds of me wanting to get a mirror out to check the headmark are even smaller.

[Russ S.]

Re: Rear spring outer bolts/castle nut

Russ------

There's no way those bolts were originally installed on a 1966 Corvette. Those bolts are GM #351592 and they did not even exist until mid-1974.

Joe, Ok. I am surprised the bolts on my 66 aren't original as I bought the car in 79 with an original spring still in it but I guess it sure is possable someone changed the bolts between 74 and 79.

What head markings and length are suppose to be in a 66?

Thanks for the correction.

[Ronald L.]

Re: Rear spring outer bolts/castle nut

Russ,
Original head marks over the years is where I started with this...

Personally I would not touch ANY of the repro stuff NONE, heads marks from far off continents that no one has ever seen on original cars, or no head marks at all. How can you assess quality and safety with that strong of unknown in a critical fastener as this.

In that data of collected bolts over several decades, SBC & P head marks fit the original design and looked old a worn. I chose to go with safety with a new black set of C head mark with 5 bars. The alternatives were Z or C in Zinc coating 5 bars, C with six in black coating.

5 was the original spec and the guy that probably knows off the top of his head that exact difference between 290M and 300M isn't on the forum, so finding that out defers to others or waits.

With a little more work we will probably fine tune it to this:
Originals: SBC, P at some time late 60's C is introduced. Rockford 92 and its derivatives for a couple of 1970's model years were discussed, and then zinc...probably a 1980 thing from other events that happened around that time. And finally the 1st post production service part as a 6 bar C.

Knowing this from about 100 bolts many still in GM wrappers - how can you trust a repro with no marking on the head, or RBW markings on the head only just because RBW was a good head mark for the 60's???

[Dick W.]

Re: Rear spring outer bolts/castle nut

FYI almost all the bolt manufacturers have left the country. Moved off shore. You have no clue as to where most bolts are manufacturered today. Saving grace though, after a major problem with counterfeit bolts 10 or so years ago, our government has come down on substandard fasteners, and for the most part, no matter where they come from they meet the specs of grade 5, 8 or whatever

[Don L.]

Re: Rear spring outer bolts/castle nut

Use a new one, and as a judge I would expect it to be black.

The odds of me seeing the head mark are quite small. If everything else looks correct, the odds of me wanting to get a mirror out to check the headmark are even smaller.

Patrick, this one's not my normal/anal approach for judging detail. Like you, I don't think any judge will want to stand on his/her head long enough to tell how many marks are on my spring bolts.

I'm concerned for the strength of the new bolts I have, being as their markings don't match the ones that are in the car presently. The ones in now are a dead match for the original bolts shown in this thread. I need to decide - aged/tired(?) vs new/uncertain. Since Ron advises that the bolts I have were seen as new GM in the 90's, I gain some level of confidence in the new ones.

Has anyone ever tested a bolt marked to be certain a particular grade and found it to be counterfeit? I could have that done in my metallurgy lab here at work, however, I'd of course lose the bolt in the process. If anyone has an extra...

[Ronald L.]

Re: Rear spring outer bolts/castle nut

Don, Music to my ears! Where is your lab? I'll donate the RBW's that I took off that I see are sold by a MI supplier. As far as other old bolts, I'll have to ask my source and are there other willing to donate old bolts to the cause?

[Wayne M.]

Re: Rear spring outer bolts/castle nut

.....5 was the original spec and the guy that probably knows off the top of his head that exact difference between 290M and 300M isn't on the forum, ....

Ron: ASTM A370 is the spec; 290M and 300M refer to grades of tensile strength (I'm guessing that it's ultimate yield -- ie. pulled to failure, and guessing again that the units are lb/sq.in -- ie. 290M = 290,000 psi).

Maybe someone with the spec. manual or the knowledge could confirm.

[Joe L.]

Re: Rear spring outer bolts/castle nut

Joe, Ok. I am surprised the bolts on my 66 aren't original as I bought the car in 79 with an original spring still in it but I guess it sure is possable someone changed the bolts between 74 and 79.

What head markings and length are suppose to be in a 66?

Thanks for the correction.

Russ------


I would say that the bolts on your car were changed sometime between about mid-1974 to July, 1980. The GM #351592 bolt, used in PRODUCTION for some 1975+ Corvettes, was also the SERVICE bolt for all 1963-74 Corvettes during that period. Of course, it's possible the replacement was done after July, 1980 if bolts were purchased out of dealer shelf stock which went into their inventory before July, 1980.

5 lines with a "C" in the center is one of the known headmarkings from the 63-74 period. There may well have been others, though.

What is the finish on the 351592 bolts you have?

[Russ S.]

Re: Rear spring outer bolts/castle nut

Joe, I had them re-finished black oxide as that is what they appeared to be. BTW the bolts on my 73 (which I bought new in 1973) appear to be black oxide and have a head marking of L7 with five slashes.

[Gary B.]

Black phosphate vs. Black oxide? Why one vs the other

... And that newer black coating was not black phos, it was a much heavier coating that took lots of effort to scrub off and verify head marks.

Ron,

Do you know if both black phosphate and black oxide treatment were used for chassis bolts, nuts, washers, during the C2 and C3 era? If both were used, what was the likely criterion that dictated one vs. the other? Was there more black phosphate during the C2 era vs. the C3 era? Or vice versa?

Thanks,

Gary