fiberglass/composite rear spring

[Mel S.]

I want to replace the rear spring on my 66 convertible 350 motor with a fiberglass/composite one. The question is that I see different spring weighs to pick from - 315#, 340# and 355#. I want a nice "non-choppy" comfortable ride. Any information will be appreciated.
Mel

[Gary B.]

Re: fiberglass/composite rear spring

Mel,

Are you aware that the spring rates you quote are MUCH higher that what came on your ‘66 originally, presuming you had the standard, two-stage 9 leaf spring?

The rwo-stage, 9-leaf spring used from 1964 thru 1974, GM #3850839, has the following spring rates:

140 lb/in @ design load of 1360 lb
196 lb/in @ design load of 1965 lb


So even the lowest fiberglass spring with a rate of 315 lb/in is more than double the initial spring rate of the 9 leaf. I don’t think anyone sells a fiberglass mono leaf spring that comes close to the 140 lb/in rate.

Gary

[David H.]

Re: fiberglass/composite rear spring

I want to replace the rear spring on my 66 convertible 350 motor with a fiberglass/composite one. The question is that I see different spring weighs to pick from - 315#, 340# and 355#. I want a nice "non-choppy" comfortable ride. Any information will be appreciated. Mel

Mel

Answer will vary depending on your choice of spring manufacturer (brand). Whose spring do you intend to use?

Ride quality is a combination of spring and SHOCKS - recommendation from both Manufacturer and users for quality shocks.

Numerous threads on CF re composite springs and paired shocks.

My car is a WIP, I have not driven it with new spring/shocks. After review of numerous threads and manufacturer recommendations, I went with a 355# TRW spring with Bilstein Heavy Duty shocks on front and Bilstein Sport shocks on rear. HD front with Sport rear is a common recommendation for ride quality. Bilstein Sport reportedly do a good job of damping rear fiberglass spring. (1980 originally with FE7 suspension)

Dave

[Mark E.]

Re: fiberglass/composite rear spring

I installed a 330# composite spring from VBP (who I think is out of business) on my 454 car. The ride is stiff and choppy, and the car sits about 1" too high. Look for a recent thread I started about shocks which discusses this. It's baffling why Corvette vendors represent these stiff springs as "smooth riding".

So I'll either restore and reinstall the original spring or get a lighter composite spring. Here's a company which offers a 180# spring:

https://hypercoilonline.com/leaf-springs-1/corvette-composite-leaf-springs/c3-corvette-high-performance-street-series/

I don't know anything about this company; Google just found it.

If you choose composite, ask a lot of questions about ride quality and height.

[Mel S.]

Re: fiberglass/composite rear spring

Thanks to all. Good information. I will do more research
Mel