Restoring spring bolts

[Anthony C.]

Hi , I am restoring my 70 project and changing the rear spring bolt cushions . I have the cushions already and was thinking of reusing the old original hardware ( washers, bolts , and castle nuts. . Would this be a wise choice being they are 50+ yrs old or should I just buy a new kit . Regards Tony ..

[Gary B.]

Re: Restoring spring bolts

Tony,

You will get differing opinions about reusing those bolts. That question has appeared multiple times in the archives, with the same recommendations as in this older thread.

https://www.forums.ncrs.org/showthread.php?16506-C2_rear-spring-bolts&p=81584#post81584

[Ron G.]

Re: Restoring spring bolts

Anthony,

I think first you need to determine what your objective is what you're gonna do with the car. Are you going to have a judge or just drive it and have some fun with it. If it is the latter, I would probably change out the bolts. If you're gonna run it through the system to have it judged and you're both in good shape, they're straight they're not pitted then I would have them replated. Their original finish was black phosphate.

[Joe L.]

Re: Restoring spring bolts

Anthony,

Their original finish was black phosphate.

Ron------


I'm not so sure about this. The spring end bolts used from 1964 through 1972 were GM #3831585. The original bolts on my 1969 were definitely either zinc or cadmium plated. For 1973-74 the bolt changed to GM #6271686. I do not know the finish of this bolt.

The last available bolt, GM #458982, which was used in PRODUCTION from late 1977 thru 1982 and SERVICE for all 1963-82 after July, 1980 was black phosphate finished.

[Ron G.]

[Joe L.]

Re: Restoring spring bolts

Joe,

the concern the user had was for a 1970 Corvette not a 69. Every 70–72 Corvette, spring bolt I ever looked at was always black phosphate. Actually, the majority of all 68–69 Corvette, I've seen were also black but they could've been a silver bolt as well I just haven't seen it and I have judged and we looked at a lot of chassis

Ron------


Yes, but the same spring bolt was used for 1964-72, GM #3831585. Unless there were optional finishes specified, they should all have had the same finish. Also, keep in mind that the spring bolt available from GM for SERVICE since 1980 has been black phosphate finished. So, I wonder how many of the cars you've seen actually have had their original spring bolt and not a SERVICE replacement installed sometime after 1980?

One other thing to keep in mind: GM specified in the factory service manual that whenever these bolts are removed from the car for any reason, they should be replaced. I expect that GM dealer service departments would have taken that seriously since it was actually quite rare for GM to specify mandatory replacement for any other fastener on the cars. So, if a Corvette came into a dealership service department for, say, the spring cushion replacement, the bolts would likely have been replaced.

It is possible that there were alternate finishes specified for these bolts. If black phosphate was one, certainly zinc or cadmium plate had to be another. As I mentioned, I am absolutely certain that my original owner 1969 originally had the latter. And, I'm just as certain that my car would not have been the only 1964-72 ever built with bolts so-finished. However, at the very least, I do not think that any car should suffer a judging penalty for zinc or cadmium finished rear spring bolts.

By the way, my car has black phosphate finished bolts on it now but not to conform to any judging standard. It's just because that's all that has been available from GM for 44 years and I choose to follow the GM admonition that the bolts should be replaced whenever removed from the car for any reason. Is it actually necessary that these bolts be replaced whenever removed from the car? Ever see what happens if one of these bolts breaks with the car on the road?

[Ron G.]

[Paul Y.]

Re: Restoring spring bolts

I have, and it was a mid year on Independent Pass just on the Aspen side of the summit above timberline with a cliff on the other side with thousands of feet drop off. These local boys were very blessed that day and I don't think they even had a clue. Declined any assistance as they had a tow vehicle enroute.

[Joe L.]

Re: Restoring spring bolts

Joe,

I don't doubt for one moment that when you bought your car New, if you say they were silver, then they were silver. Again, I am referring to our cars with super low mileage and not just one or two lots of them. Again, I'm referring to this gentleman 1970 Corvette. I never seen a super low mileage 70–72 Corvette with Silver Spring bolts not to say that it didn't happen. I'm just sharing my experience in opinion.

Ron------


Assuming that the 3831585 all had a zinc/cadmium finish, I suppose it's possible that the GM #6271636 was factory-installed well before the AIM's indicate in 1973. I would not expect this part number as early as 1970 but it's possible for 1971 or, especially, 1972. As I mentioned previously, I know nothing about the 6271686; it could very well have had a black phosphate finish.

Do you know what the manufacturers' ID head marking(s) have been on the 70-72 models you are familiar with?

Attached are photos of an NOS GM #3831585. Note that the packaging is very old style GM; very likely from the later 60's-early 70's. This bolt has a natural, machined steel finish unlike either a zinc/cadmium or black phosphate. It's very similar to the 1975-E77 bolt, GM #351592, except it does not have the "92" headmarking.

GM#3831585bolt(a).jpgGM#3831585(b).jpgGM#3831585(c).jpg

[Jeffrey S.]

Re: Restoring spring bolts

I'm not sure this helps, but I believe this is the original spring bolt from my Oct '68 car.
Jeff

[Joe L.]

Re: Restoring spring bolts

I'm not sure this helps, but I believe this is the original spring bolt from my Oct '68 car.
Jeff

Jeff-----

I'm very confident it's original.

[Jeffrey S.]

Re: Restoring spring bolts

Joe,
Thanks for that. I don't know why I replaced these- it was at least 10 years ago.
Jeff

[Mark E.]

Re: Restoring spring bolts

Joe,
Thanks for that. I don't know why I replaced these- it was at least 10 years ago.
Jeff

Maybe because the threads are badly corroded.