C-2 9 leaf vs 7 leaf hd

[Jim R.]

would it be a mistake to run a 7 leaf hd on a 63 that came with a 9 leaf originally, the spring i would buy would be a repop...also front springs are standard.

[Joe L.]

Re: C-2 9 leaf vs 7 leaf hd

would it be a mistake to run a 7 leaf hd on a 63 that came with a 9 leaf originally, the spring i would buy would be a repop...also front springs are standard.

Jim------


Many years ago when GM discontinued the 9 leaf, standard suspension rear leaf spring, they replaced it with the 7 leaf HD spring for SERVICE. So, GM apparently considers the 7 leaf spring an acceptable replacement for cars originally equipped with the 9 leaf.

I don't think you'll have any problem, at all, using the 7 leaf spring in place of a 9 leaf.

[Duke W.]

Re: C-2 9 leaf vs 7 leaf hd

. Without a corresponding increase in front roll stiffness via increased spring rate or a larger anti-roll bar, the handling would be biased toward more oversteer.
Messing with springs and bars can have serious negative consequences, which most guys who do no have a firm foundation in vehicle dynamics do not understand.

Duke

A mild understatement Duke. Get into an emergency situation, and the car becomes a monster to handle

[Joe L.]

Re: C-2 9 leaf vs 7 leaf hd

. Without a corresponding increase in front roll stiffness via increased spring rate or a larger anti-roll bar, the handling would be biased toward more oversteer.
Messing with springs and bars can have serious negative consequences, which most guys who do no have a firm foundation in vehicle dynamics do not understand.

Duke

A mild understatement Duke. Get into an emergency situation, and the car becomes a monster to handle

Duke------


I highly doubt that GM would have replaced the 9 leaf spring for SERVICE with the 7 leaf if there would be any significant problem in doing so, especially if a safety issue were involved. They could just as easily have discontinued the 9 leaf spring without supercession. In fact, in a case like this, that's what they usually do.

[Duke W.]

Re: C-2 9 leaf vs 7 leaf hd

I didn't know that GM substituted the HD spring for the base spring when the latter was discontinued (which is what I think you are saying), but I do know that whatever "engineering evaluations" are done for substitute parts may be cursory.

That cost me two lower radiator hoses on my Cosworth Vega because the GM replacement alternator belt was longer than OE, which caused it to rub against the hose. Clearly this substitution didn't receive much if any "engineering evaluation".

From my own experience I know that the '63 spring/bar setup is on the ragged edge of stability. The steering is very responsive with minimal understeer, but my SWC became a handful for me a few times at the limit, and I lost it twice (on public roads) - the only two times I have ever totally lost control of a car, which includes 35 years of racing and race track hot lapping. Those two spins were back circa 1965. The first time the road was wet, and the second time I was wet! At the time the car was shod with 6.70-15 Michelin X radials, and they had excellent grip for the era, but a well-deserved reputation for "sudden breakaway".

My advice to the OP is to search out a substitute rear spring that is closer in spec to OE, rebuilt the original, or find a rebuildable original.

Springs rarely "wear out" unless they are damaged in service due to overloading or collision. The other thing that gets them is corrosion. If a used spring has no serious corrosion and no evidence of damage, it is easily rebuildable with a cleanup, painting, and new liners.

Install it with new spring link cushions, and it will be like new.

Duke

[Michael H.]

Re: C-2 9 leaf vs 7 leaf hd

My advice to the OP is to search out a substitute rear spring that is closer in spec to OE, rebuilt the original, or find a rebuildable original.


Duke

I've driven two cars so equipped and owned another. The HD rear spring (without HD fronts) made the car... scary, to say the least. No problem in a normal turn but as soon as the issue was pushed a bit, things quickly/suddenly became very interesting.
I understand that GM may have recommended this combination at one time but if it were my car, I would find a rear spring somewhere near an original in rate, as Duke suggested.

[Michael F.]

Re: C-2 9 leaf vs 7 leaf hd

or replace the front springs to match the rear 7 leaf....sway bar also as required

[Duke W.]

Re: C-2 9 leaf vs 7 leaf hd

No problem in a normal turn but as soon as the issue was pushed a bit, things quickly/suddenly became very interesting.

Most owners would never know until the day comes that they have to take rapid evasive action. Then the car just snap spins totally out of control, and they never saw it coming.

That's why I run my cars on tracks and take advantage of freeway ramps whenever possible. I want to know how my cars respond at the limit, and if it ain't right, I fix it!

When I bought my '91 MR2, I thought I had made a big mistake. At the limit it acted like a '65 911. The fix was easy - 20 mm larger rear section tires in the same aspect ratio, which added 400 pounds load capacity to the rear and brought tire load capacity distribution in line with vehicle weight distribution. It also corrected the highly optimistic speedometer.

This brought the handling to near nirvana. Dan Gurney was reported to have helped with final tuning of the suspension on Angeles Crest Highway. I've always wanted to ask him if he likes oversteer. The 7" wheels and fender wells had plenty of room for the bigger tires, and my hunch is that the tires were "downsized" 20 mm just before start of production to allow the installation of tire chains.

Toyota recognized the "problem" and completely redesigned the suspension for '93, and those later models have slower responses with a lot more understeer and basically don't handle as well as the earlier second generation models with a proper tire setup.

All they needed was more tire load capacity in the rear.

My Cosworth Vega also had a rapid transition to oversteer at the limit. Also an easy fix - hard urethane bushings on the front anti-roll bar links in place of OE rubber. In fact, the first set I installed were off a Firebird Trans Am. Ever since it's been perfect dead neutral. Guys who rode with me at track events were always amazed.

I recommend the same thing for C2 Corvettes. I'm not sure about C3s. The reason they redesigned the rear strut rod bracket was two fold - less camber change for the wider tires and it also lowered the rear roll center for less roll stiffness, which added a bit more understeer bias, but I remember a ride in a friends '70 L-46 on Mullholland several decades ago. He was pushing hard and the car felt pretty edgy. I told him he was going to spin, and that's exactly what happened on the next corner! ...no damage other than his bruised ego.

Duke

[Bill M.]

Re: C-2 9 leaf vs 7 leaf hd

In addition to the handling issue, the 7-leaf is very stiff in ride.

Chevy restricted its use as an option to the highest-performance engines because it is just too stiff for a daily driver (unless you're in your 20s!)

[Glen S.]

Re: C-2 9 leaf vs 7 leaf hd

Eaton Spring has a 9 leaf available that closely resembles the original 9 leaf spring.

http://www.eatonsprings.com/index.html

[Harry S.]

Re: C-2 9 leaf vs 7 leaf hd

Jim, there are original 1963 9 leaf springs out there. It may take some time to find one. Remember, the 1963 9 leaf spring is a 63 only spring, so know what they look like. I found one last year and paid about $300.00 for it. I then restored it with a Quanta kit.

[Rick S.]

Re: C-2 9 leaf vs 7 leaf hd

"I then restored it with a Quanta kit."

Harry, unfortunately the Quanta is not currently available, as I inquired of them that I couldn't find it on their website last week and got this response:

We cannot supply the paint at this time and are in the process of reworking the price on the kits. Sorry for any inconvenience.

Quanta Products LLC.
743 Telegraph Road
Rising Sun, MD 21911
(410)658-5700 (800)235-8788



Rick

[Steven S.]

Re: C-2 9 leaf vs 7 leaf hd

Duke, I wish I had your suspension knowledge, it certainly seems you have a very good understanding of it.

Steve

[Duke W.]

Re: C-2 9 leaf vs 7 leaf hd

A good primer on the subject, which is meant for the non-engineer enthusiast is Fred Puhn's "How to Make Your Car Handle". It's old, but the basics haven't changed, and I think it is still in print.

Duke

[Joe L.]

Re: C-2 9 leaf vs 7 leaf hd

About 10-12 years ago a friend of mine with a Corvette shop purchased a very original 1968 Corvette from an estate sale. The car was an original owner which was purchased new by a fellow that was an inspector for the California Department of Transportation (CALTRANS). He drove the car day-to-day until about 1978 (the last registration sticker on the license plate expired in 1978). Then, the car was stored in his garage, apparently never to be driven again by him. After his passing, my friend purchased the car from the estate.

The car was a coupe with 300 hp 327 and THM-400 transmission. It was LeMans Blue with Medium Blue vinyl interior. I don't recall the serial number, but I do recall it was a VERY early build car.

I had a chance to inspect the car thoroughly, including the chassis since it was on a lift in my friend's shop. MOST unfortunately, I took no notes and took no pictures. I could kick myself for that now. Anyway, among some other things I remember is that the car was equipped with the original rear shocks and, apparently, the original rear spring. The shocks were the HD, "coullee hat" shocks and the rear spring was a 7 leaf. I recall looking at these very carefully and I am virtually certain they were original to the car. The shocks had 1967 dates on them. The front stabilizer bar was a 3/4" unit. I do not recall, if I even inspected them at all, what the front springs and front shocks were.