'69 leaf spring replacement/revival

[Peter Rastello (33299)]

I went in for new tires and an alignment last weekend only to be told the car is currently not align-able. Seems the leaf spring is almost completely flat, and the adjustment cam already maxed out. Rear wheels are visibly out of camber. The alignment guy mumbled something about having the spring re-arced, but I'm not sure that's the best way to go.

I've looked throught the 'Zip' catalog and found 7-leaf, 9-leaf, and high performance fiberglass springs rated at 315+ lb/in spring rate. Those of us who read 'Leaves of Spring' by Gary Beaure in the last Corvette Restorer know that I should be looking for a two-stage, 9-leaf with a 140 lb/in spring rate.

Okay. So, since Zip doesn't seem to be in the know: 1) where should I look? 2) Can my original be 're-arced' as suggested? 3) Any follow-on comments to the referenced article as far as spring rate? 4) How about the fiberglass version (assuming for one rash moment that I don't really care about maintaining my current NOS correct vette).

Thanks in advance, Pete.

[Joe L.]

Re: '69 leaf spring replacement/revival

Peter-----

The situation that you describe does not necessarily mean that your rear spring is "worn out". In the loaded circumstance, the spring is supposed to be nearly flat. Some folks mistake this condition for a worn out spring. If your spring is lower in the center than at the ends when its in the loaded condition, then you have a worn out spring, for sure.

The inability to achieve a proper rear camber adjustment within the range of the adjusting cams is a common 63-79 Corvette problem. It can be caused by a worn out spring but it can also be caused by several other deficiencies. These include worn inner ends of stub axles(VERY COMMON problem), worn positraction clutch packs, and distorted/deteriorated strut rod end bushings.

The rear spring is far too often blamed for the camber adjustment problem. However, if you do need a spring, I don't recommend "re-arching". Purchase a new spring.

[Duke W.]

Re: '69 leaf spring replacement/revival

Have you replaced your spring cushions? After 31 years they compress and harden. This causes the rear end to sag while simultaneously increasing negative camber. Renewing the cushions will restore ride height and probably bring rear camber back into spec, or at least allow it to be adjusted to spec. The four cushions are available from GM and other sources for about 10 bucks list, and it's an easy DIY job. With the car on the ground use a floor jack and wood block to jack up the end of the spring until the links is free. Then remove the link and reinstall it with the new cushions. The other major benefit will be a significant reduction in ride harshness.

Wear and comprssion of the spring liners can cause the same problem, but the magnitude of sag would be small compared to compressed cushions. Springs rarely "wear out" unless they are overloaded because steel has virtually no measurable "creep" characteristic. Old bridges and buildings do not sag or wear out unless they are seriously overloaded or corrode away. If you do replace your spring for whatever reason, replace it with the same rate. In addition to significantly roughening the ride, a significantly higher rate rear spring will add substantially more roll stiffness to the rear which will cause the car to oversteer more unless the front is stiffened up with higher rate springs and/or a bigger anti-roll bar to maintain the same front/rear roll stiffness distribution.

Duke

[Patrick H.]

Re: '69 leaf spring replacement/revival

Peter,

I agree. I find that the strut rod bushings are a problems as much as, or more, than anything else. These babies seem to wear out very quickly, despite miles or lack thereof.

Close inspection will likely show that you have a few of the aforementioned problems, but at least the bushings here are somewhat easier to see when they squish out.

Patrick