C-3 rear spring question: Mono spring vs 9 leaf

[Robert M.]

Hi all,
I have a question about rear springs, and hope to get some good knowledge input.

I have a 1970 small block roadster. It's meant to be a nice driver. About 18 years ago I bowed to marketing pressure and installed the TRW Rear Mono Spring. I think it is the 330 lb model. The 9 leaf spring originally installed had a much lower rate, which I fail to recall.

My question is this: Do I have get a better ride with the stiff TRW Mono Spring, or the soft 9 leaf spring, and what are the pluses and minus' of each spring?

It's been so long ago I don't remember how the 9 leaf spring felt, handled.

[Timothy B.]

Re: C-3 rear spring question: Mono spring vs 9 leaf

Robert,

I think you will get a better ride with the stock 9 leaf spring. If it's in nice condition put it back and try it.

Install new rubber donuts where it attaches to the trailing arm and don't torque the four rear cover bolts until the weight of the car is on the ground.

[Jim T.]

Re: C-3 rear spring question: Mono spring vs 9 leaf

Robert my 1970 original owner coupe's rear spring was allowing the car to bottom out going down the highway on a trip with the back loaded with stuff. I changed the rear spring at least 21 years ago since my 70 was a daily driver and used on almost all road trips since it had air conditioning. I installed the Vette Brakes composite 360 spring. I liked the performance change of the stiffer composite spring after changing it and still like it today. Another change I liked with the composite spring was the reduction of the Corvette squat with strong acceleration. My 68 convertible 327/350 4-speed with strong acceleration would of course still do the Corvette squat. After seeing the difference with the general overall ride of the composite spring I installed the same type of composite rear spring on the 68. Sure don't miss the Corvette squat when I get on it and I do like the difference in the 68's ride.
Rear springs are really pretty easy to change on my 68 and 70 drivers if I were to have them judged.
One of the things that helped me make the initial decision to go with a composite spring instead of a new replacement for my 70 many years ago was that the 81 automatic Corvettes and all later years of Corvettes use composite springs.
I would not install my original 70's rear steel spring again unless I was going to have it judged.

[Duke W.]

Re: C-3 rear spring question: Mono spring vs 9 leaf

I think by 1970 Chevrolet went back to a constant rate sping as in 1963, and the '63 rear spring rate is about 162 pounds/inch, so this aftermarket spring is about double the OE rate - actually a little higher than the F-40/41 HD spring, which is 305 lb/in.

This has two effects. It significantly increases the rear ride rate, which will appear as a "stiffer" ride, and it will need a significant increase in rebound damping to control body bounce - both due to the increased ride rate and the inherent lack of damping in a composite spring compared to a multi-leaf steel spring.

The increased rear ride rate also increases rear roll stiffness, and if there is not corresponding increase in front roll stiffness relative balance will bias toward oversteer.

I've discussed this a zillion times, but will say again that these springs do not "wear out" in the traditional sense. What can kill them is corrosion!

Loss of rear ride height (and increased harshness) is usually the result of compressed and hardened spring link cushions. This is the cause of "sag" and it also causes an equivalent loss of jounce travel, which increases the propensity to bottom.

These problems are easily solved with a few hours labor and a few dollars in parts. Remove, disassemble, cleanup, and inspect all the leaves. If there is no serious corrosion, they are perfectly serviceable. I recommend applying a corrosion resistant coating to the leaves, but this gets into some judging issues, so each individual has to make a choice between OE appearance and additional corrosion protection.

Reassemble the spring with new liners and install on the chassis with new link cushions and as new ride height and suspension performance will reappear.

Duke

[Jim T.]

Re: C-3 rear spring question: Mono spring vs 9 leaf

I did also change my front springs in my 70 with the addition of the composite rear 360 spring. Installed the "518" GM springs.