Leaf spring identification

[Thomas B.]

This spring is on my 63. I think I see 9 leaves, 7 liners. May have been installed in the 80s when car was restored but not sure. Has a 7” rise from bolt holes to bottom at center of length as installed in the car with the ends not connected per the picture. Doesn’t look like any I’ve seen on the market today.

The short top leaf is thick like the bottom leaf and the other 7 leafs are thin.

Defibitely not and original 63 spring. I'm trying to determine if this is a standard or heavy duty spring.

Thanks for any input.

[Alan D.]

Re: Leaf spring identification

Would think you need to remove, bring to spring shop and have them measure the characteristic. If you plan to show the car, just get the correct looking spring.
Also note the camber bolt is in wrong direction and is later incorrect replacement part, the posi label may be incorrect.

[Thomas B.]

Re: Leaf spring identification

Alan, thanks for pointing out the incorrect parts and the spring shop idea. Seems to be a heavy duty replacement from sometime in the distant past. Only has a 7” arch and some arch remains with the weight of the car on it. Not very scientific, just my impression. I was thinking of replacing it with a 6/3 spring and hopefully soften the ride quite a bit. I believe the front coils and front sway bar are stock.

Zip Corvette have those:

https://www.zip-corvette.com/63-82-strut-rod-camber-adjusting-kit-reproduction.html

https://www.zip-corvette.com/63-64-differential-metal-tag.html

[Joe L.]

Re: Leaf spring identification

This spring is on my 63. I think I see 9 leaves, 7 liners. May have been installed in the 80s when car was restored but not sure. Has a 7” rise from bolt holes to bottom at center of length as installed in the car with the ends not connected per the picture. Doesn’t look like any I’ve seen on the market today.

The short top leaf is thick like the bottom leaf and the other 7 leafs are thin.

Defibitely not and original 63 spring. I'm trying to determine if this is a standard or heavy duty spring.

Thanks for any input.

Thomas------


This is not a GM spring of which I am aware of any origin, PRODUCTION or SERVICE, for any Corvette application.

[Thomas B.]

[Duke W.]

Re: Leaf spring identification

The '63 base/Z-06 spring rates are 280/550 lbs/in and the rear rates are 162/305 lbs/in. These spring rates aren't the actual rates you feel What you feel are the wheel rates. Due to the leverage of the front control arms the front wheel rate is about 80 lbs/in, but the leverage on the rear spring is much less. so the wheel rate is only slightly less than the spring rate. The actual slips my memory right now, but it's probably about 140 lbs/in.

The rear has a higher rate because as the car is loaded, most of the weight of people and cargo is born by the rear. Also different front and rear wheels rates help attenuate pitching motions on short wheelbase cars, and if you've ever ridden in a Smart car you can probably remember the hobby horse pitching motions, which are not very pleasant.

Based on the wheel rates and respective loads the ride frequency can be calculated. This is the frequency that the front and rear would oscillate at if it were frictionless and you raised or depressed the body at end and then released.

Again I can't recall the exact ride frequency I computed, but with base springs the front is no more than 1 Hz and the rear is maybe 1.5 Hz. This is why base suspension C2s have decent ride quality. The HD springs double the wheel rates

The high roll centers mean that the springs provide considerable roll stiffness, so for small blocks only the front has a modest size anti roll bar. Increasing the spring rate, antiroll bar diameter, or adding a bar on an end where there was none will increase roll stiffness. If the front it will increase understeer, and if the rear it will increase the propensity to oversteer, and since C2 small blocks are already pretty neutral, anything that increases roll stiffness at the rear without a compensatory increase at the front can cause a dangerous oversteer condition at the limit. Note that both the Z-06, F-40, and F-41 spring and bar combinations actually increase understeer because these HD setups were designed for big track road racing, so a little more understeer bias is a bit more forgiving.

If you can find a serviceable or at least rebuildable '63 base spring you would be wise to procure and install it.

Increasing spring rates on base suspension Corvettes is not a good idea unless you are seriously racing. It will not really improve "handling" which is mostly a function of tire grip, but will considerably stiffen the ride. I recently rode in L-78 with F-40 on Southern California's deteriorating roads and the ride was punishing!

Also standard replacement shocks don't have enough rebound damping to control a stiffer spring, so the ride ends up bounty.

If you want better "handling" get rid of the cheap. junky, low speed rated tires that have a wear rating of 600, and replacement them with some serious performance tires. At best the former generate about 0.75g lateral on a level surface no matter what you do to the suspension.

Duke

[Thomas B.]

Re: Leaf spring identification

Duke,
As always very enlightening. Had no idea about the oversteer implications of increasing rear spring rate. So I take it that small block C2s were set up not to have a propensity for excessive oversteer or understeer and for a sporty but comfortable ride.

I definitely want to change the spring since the ride is quite stiff and bouncy or choppy and add to that the dangerous oversteer condition. Do you feel the readily available 6/3 springs with 140/196#/in variable spring rate would be an appropriate substitution for the original 63 springs which were 162#?

[Duke W.]

Re: Leaf spring identification

Yes, C2s are quite neutral handling. They do have a bit of trailing throttle oversteer...not as bad as a contemporaneous 911, but the three link rear suspension has a lot of toe, camber and track change with jounce and rebound along with poor anti-squat characteristics, which can make a C2 a bit dicey at the limit, especially if you lift off the throttle, which unloads the rear suspension causing changes in camber, toe, and track.

Handling is very sensitive to static rear toe setting and any amount of static toe-out can make it feel like it's possessed by the devil. A couple of years ago I helped an owner correct a severe handling instability (oversteer) due to the right rear having a bit of static toe-out rather than toe-in. These cars are extremely sensitive to static toe-in and it better be in the ballpark or the car will be a beast.

For '68 the rear roll center was reduced, which reduced rear roll stiffness yielding a bit more understeer bias.

If you can't find a '63 constant rate rear spring, the '64-'67 variable rate spring should work out okay.

Duke

[Harry S.]

Re: Leaf spring identification

63 9 leaf spring.

Before, notice no liner between leaf 1 and 2.

Spring (3).jpg

After, just needed liners and a new bolt.

Spring (12).jpg

[Thomas B.]

[Thomas B.]

[Harry S.]

Re: Leaf spring identification

Harry,
Is your spring an original 1963 9 leaf spring? Very nice. Interesting that all of the leaves seem to be the same thickness, compared to my repro spring with the thick top and bottom leaves and 7 thin leaves in between. Yours should have an even higher spring rate than mine.

Yep, it's an original spring.

[Duke W.]

Re: Leaf spring identification

The 64 -67 spring should provide a softer ride looking at the spring rates for each. Wasn’t that the reason for the different spring for 64 - 67. The 63 spring was too stiff?

After the '63 went into production the engineers went to work on NVH (noise, vibration, harshness). That's why rubber isolators were added to the body mounts and numerous other minor changes that continued to the end of C2 production.

The thought on springs was that variable rates would improve ride quality without sacrificing handling, but I think they went back to constant rate springs in '68.

Duke

[Gary B.]

Re: Leaf spring identification

[Joe L.]

Re: Leaf spring identification

After the '63 went into production the engineers went to work on NVH (noise, vibration, harshness). That's why rubber isolators were added to the body mounts and numerous other minor changes that continued to the end of C2 production.

The thought on springs was that variable rates would improve ride quality without sacrificing handling, but I think they went back to constant rate springs in '68.

Duke

Duke------


1968-74 rear springs were the same ones used for 1964-67. The 68+ front springs were different but were still variable rate design.