Attn Joe Lucia Please Lend Us Your Brain(s)

[Chuck S.]

In an effort to help a fellow Vette owner, Duke, I, and several others have discussed, researched, argued, measured, and generally exhausted and confused ourselves into an impasse.

The subject of the original thread was a '78 that "squats", i.e. had ride height lower than design. The discussion turned to spring hanger bolts. Even we know that the C2s and earlier C3s had spring hanger bolts (3831585) that were 6.25" long. But, I am sure I bought some spring hanger bolts by mistake at a Bloomington swap meet that were 1"-1.5" shorter; they had the same head stamp (which means nothing in itself), with the same reduced cross-section shank, 9/16"-18 threaded end, and cotter pin hole in the end. When I discovered my error, I thought they were for a later C3, but I can't confirm that. Can you give us a thumbnail history on C2/C3 spring hanger bolt applications, service part revisions, etc.?

Also, I maintain that IF the '78 originally used the shorter spring hanger bolts, the inadvertant use of longer bolts would cause the car to "squat"; Am I right? I believe Duke takes the counterpoint, but I'm not sure anymore.

Please...give us some relief here!

Chuck Sangerhausen

[Duke W.]

This probably doesn't help, but...

I just measured the spring link bolt shank length on a neighbor's '77 and it looks like the same as my '63 - 6.25 inches. I helped him change the cushions a year ago to restore ride height. We found an after market link bolt on the car,so I suggested to him that he buy new bolts along with the cushions. He bought the parts from GM and when installed, it raised the rear and brought the pitch attitude back to neutral. The parts catalog indicates a change in p/n circa '75, but the question remains as to whether they had different shank lengths.

Yup, a shorter bolt will raise the ride height, and a longer one will lower it. Years ago when my '63 first began to sag I stacked a few washers between the nut and the bottom retainer to raise the rear. This effectively shortens the bolt. Later, when I realised compressed spring cushions was the problem, I replaced them and got rid of the washers. The ride height was restored, but what really amazed me was the reduction in ride harshness.

Duke

[Greg A.]

Re: Attn Joe Lucia Please Lend Us Your Brain(s)

Chuck, Duke and Others...

It was my original post that initiated this discussion. My thanks to all of you for the comments/suggestions.

I took a good look at the spring and bolts, etc. this morning and think I may know what some of the problem is. Carefully counting the spring leaves, I find it is actually just a 7 leaf spring. No FE7 on this car (no rear anti-sway bar), so I believe it should have been replaced with a 9 leaf spring. I'm not sure how this would alter the ride height, but I know it's not the correct replacement spring.

Wayne mentioned bow in the spring. It has a slight bow "up" (ends curve up slightly.) Is this the proper direction of bow? Spring bolts are 6.25" long which appears to be the standard.

Next week, I'll take it back to the shop that did the spring replacement and question the use of the current spring.

I have some photos for anyone interested...again, thanks for the assistance.

Greg

[Ol'Geezer]

Re: Attn Joe Lucia Please Lend Us Your Brain(s)

Greg --

Seems to me that the bow is inverted. Are you sure that the spring is not upside-down?

[Tony H.]

Re: Attn Joe Lucia Please Lend Us Your Brain(s)

When I bought my 1970 BB no A/C Corvette about 10 years ago, it had the 7-leaf (replacement) spring in the rear but originally had a 9-leaf spring. The 7-leaf spring gave the car's rear a lower (more squat) ride height. The previous owner told me he had replaced the original spring to the 7-leaf spring for better cornering via lower center of gravity. I eventually replaced the rear spring with a 9-leaf spring and the ride height came up to normal. Hope this helps.

[bruce 11495]

Re: Attn Joe Lucia Please Lend Us Your Brain(s)

Just a few thigs to consider 1. There was a difference in overall lengths of rear springs between years, I can't remember how much, 1.5 -2.25 sounds familiar. 2, There is also a difference in widths, the 60s cars had a wide spring hence the spacer between the spring and diff 3The ideal arch is just enough so that the car won't have that bottom out feel when you go over a dip in the road. IF the spring is straight or curled up slightly the problem to watch for is the half shafts won't travel over center. You'll break either the rear end or the half shaft or both. Hope this helps

[Duke W.]

It's just amazing, Tony-...

some of the misguided and convoluted logic that amateur engineers, like the previous owner, come up with!

Duke

[Joe L.]

Re: Attn Joe Lucia Please Lend Us Your Brain(s)

Chuck, et al-----

So you want to know about rear spring bolts, huh? Well, why don't you just ask me to prove Einstein's theory of relativity? That might be easier. But, here goes anyway:

From 1963-72, it's easy. The GM #3831585 bolt was used. This bolt was 6-3/8" long.

For 1973-74, things changed. For these years, the bolt used was GM #6271686. As far as I can tell, this bolt was about 5-3/4" long. It was discontinued from SERVICE in 1976.

For 1975, things got REAL complicated. For 1975, the standard bolt was changed to GM #351592, which was 6-3/8" long. However, in PRODUCTION other bolts were also used in order to adjust the rear bumper height. The 73-74 bolt, GM #6271686, was used to RAISE the rear bumper to the greatest degree. There was also another bolt available, GM #351591, to raise the bumper less than the aformentioned, but more than the standard GM #351592 bolt. This 351591 bolt was about 6" long. And there were two other bolts available to LOWER the rear bumper. These were GM #351593, which was about 6-5/8" long and GM #351594, which was about 6-7/8" long. The GM #351591, GM #351593, and GM #351594 bolts were NEVER available in SERVICE.

For the 1976 model year, things got a littler simpler. For this year, the GM #6271686 and GM #351594 bolts were discontinued and only the standard bolt GM #351592 and the PRODUCTION-optional bolts, GM #351591 and GM #351593 were used.

For the 1977-81 the standard bolt was changed to GM #458982. This bolt is 6-3/8" long. Also used in PRODUCTION was GM #458981, which was about 6" long and GM #458983, which was about 6-5/8" long. The shorter PRODUCTION bolt was again used to RAISE the bumper height and the longer PRODUCTION bolt was used to LOWER the bumper height. The GM #458981 and GM #458983 bolts were NEVER available in SERVICE. The GM #458982 replaced all earlier "standard length" bolts (6-3/8") to SERVICE all 63-82 Corvette applications. It remains available in SERVICE to this very day.

Why did things get so complicated in 1975 as far as spring bolts go? Well, if you recall, in 1974 Corvettes went to an impact absorbant rear bumper. However, for these bumpers to work according to FEDERAL REQUIREMENTS, bumper height (or rear "ride height", if you choose to use that term) was critical. For 1974, either the impact-absorbant bumpers were, technically, not yet a requirement (making bumper height not-so-critical from a regulatory perspective) or GM didn't discover how critical that bumper height was to meeting the standards. So, that's why all of the different spring bolts became important for PRODUCTION purposes starting in 1975. This allowed St. Louis to rather easily "fine tune" the rear bumper height.

Just to confirm once again, a SHORTER BOLT RAISES the rear bumper (or ride) height and a LONGER BOLT LOWERS the rear bumper (or ride) height.

By the way, in response to another question above, the 7 leaf HD rear spring SHOULD NOT SIGNIFICANTLY AFFECT REAR RIDE HEIGHT IN COMPARISON TO THE 9 LEAF SPRING. Acccording to GM-data, for a Corvette coupe, the difference should be negligible; for a convertible the 7 leaf HD spring should actually make the rear ride height about 1/4" HIGHER. As a matter of fact, about 10 years ago, GM replaced in SERVICE the last available 1-1/4" wide standard rear spring, GM #362153, with the last available 7 leaf HD spring, GM #354130. Unfortunately, the GM #354130 is now also discontinued.

And, lastly, in case any of you are wondering, the F-41 FRONT springs generally DO RESULT in a lower ride height than the standard front springs; however, the REAR 7 leaf HD F-41 spring DOES NOT.

From now on, you guys are going to have to start coming up with easier questions or I'm going to have to take a vacation from this place. In 2 weeks, though, I'm going to do that anyway.

[Duke W.]

Joe's vacation

We need to equip Joe with a lap top and RF modem so he can stay in touch with the Board while he's on vacation, which we know will include Bloomington.

Duke

[Chuck S.]

E=mc2

Joe,

That was a lot of work and we really appreciate it.

I have to find those old bolts, and see where they fit in this parade. I am thinking they have to be for '73-'74, 6271686, 5 3/4". Thanks again.

Now, does anyone know how we can print this stuff out with this black background? I'm afraid I will exhaust my ink reservoir and still not be able to read it.

Chuck Sangerhausen

[Roberto L.]

Re: E=mc2

Chuck, drag over the text, rightclick and choose copy, then open your favorite word processor (or Wordpad) and rightclick, choose paste. There you will be able to file the post or print it. There are other options but this one is an easy one. Roberto, NCRS #30019, RMC

[Chuck S.]

Re: E=mc2

Roberto,

Got it! Thanks.

I had to make minor revision to your instructions; I opened Word first, then went back to NDB, highlighted the text, and copied it from the toolbar. Then pulled up Word, pasted, and printed. Had a problem losing text highlight when I right-clicked on NDB.

Chuck Sangerhausen