Fiberglass vs. Composite Rear Spring

[Don O'Conell #33101]

I'm in the process of redoing the front and rear suspension on my '69 L68. Have gotten almost all of the parts. I ordered a TRW 330 lbs/in spring in early January. Kept calling every other week and was told it was on back order. In March I started looking around and could not find one in stock. Finally some one mentioned that the TRW spring line was bought out by Vette Brakes so I ordered one of theirs (don't know if they bought them out and discontinued the line).

The Vette Brakes fiberglass spring came with a note stating never expose the spring to excess heat and allow a minimum 3" exhaust clearance and to use heat shields.

My questions are:

1) Is TRW really out of the Composite spring business?

2) Does the fiberglass spring have about the same characteristics as the composite (I've got a friend with a '72 with the TRW and I really like the ride)? I'll be using it with the KYB gas shocks tuned for the composite.

3) If anyone has used the fiberglass, does someone make the heat shields?

Thanks for any advice before I commit to this one

Don #33101

[Jim T.]

Re: Fiberglass vs. Composite Rear Spring

I have the Vette Brakes fiberglass rear spring on the rear of my 68 and 70 Corvettes. I like the ride, that is why I bought the second one after trying one on the 70 first. I don't think that my installation instructions stated anything about installing a heat shield. There was a minimum amount of clearance that was specified from the two exhaust pipes under the rear spring. This was met and have had no problems yet operating without a added heat shield. What spring rate did you purcahse? Mine are both the 360. I don't have any information about the TRW buyout.

[Michael W.]

Re: Fiberglass vs. Composite Rear Spring

Don,

I have a TRW spring on my '73, not sure of the rating. Make sure that you compensate adequately for the more supple response of the new spring with your shocks. I didn't, almost got seasick from the bouncy ride!

Regarding the heat shield, my kit came with one. It's nothing more than a rectangular piece of sheet aluminum with four holes in it and mounts between the spring and retaining bracket. It keeps the heat of the exhaust pipes away from the spring where they come close to each other near the diff. cover.

Mike


Quebec NCRS Chapter

[Bill D.]

Re: Fiberglass vs. Composite Rear Spring

A shield was used by the factory on '81/82 cars with fiberglass spring.You can use that since it is a moulded and drilled piece of sheet metal.If you want or need a more substantial shield because of tight clearance to exhaust try contacting Koolmat @ 1-800-koolmat.

[Joe L.]

Re: Fiberglass vs. Composite Rear Spring

Wild Bill-----

Yes, there were a variety of exhaust heat shields used in the 81-82 period for the Corvette rear exhaust system. However, all are now GM-discontinued. They may be available in the used market, though.

[Tom Freeman]

Re: Fiberglass vs. Composite Rear Spring

Don, It was my understanding that a "fiberglass" spring and a "composite" were the same thing. Kind of like the new "fiberglass" vettes actualy being SMC, sheet molded composite.

tom...

[Jerry Clark]

Re: Fiberglass vs. Composite Rear Spring

Hi Don:

When you asked about this I shared Tom's assumption but did not feel comfortable with assumptions in this regard. Vette Brakes are the ones to straighten this out for sure but it sounds a lot like technospeak to me, lets baffle em' with bull. My Fiberglass spring was purchased almost five years ago and came with no such shielding requirements, didn't install one and with the KYB shocks the ride quality is excellent.

jer

[Gerald Lee]

Re: Fiberglass vs. Composite Rear Spring

I don't know much (read nothing) about composite springs and KYB shocks but I have them. My question is there a way to tune the KYB's or do you have to purchase the correct valved shock for the application. My '66 SB is very bouncing when going over normal dips in the road (the rear only).

Regards,

Gerald Lee #31112

[Duke W.]

Re: Fiberglass vs. Composite Rear Spring

Assuming you have the de Carbon (high gas pressure) KYBs, it sounds like they may have failed. Is there any evidence of leakage. The fiberglass rear spring should not require a significantly different shock than a similar rate steel spring. If the gas pressure leaks out the shocks will go limp. Normal twin tube shocks degrade slowly over their service life, but high pressure gas shocks generally maintain their damping characteristics throughout their life, and then go away completely.

Duke

[Gerald Lee]

Re: Fiberglass vs. Composite Rear Spring

Hi Duke,

Thanks for the response. Actually, the shocks were just recently installed and the car has fewer than 1500 miles since restoration. When I say bouncing, I don't mean like a basketball. An example would be, when I go over a dip the car rebounds more that the compression. At least it seems that way. It definately does an extra bounce. I'm so new to the hobby that I don't really know if this is normal. My Tahoe or other cars don't produce the same effect on the same dip.

Thanks in advance for any advice.

Gerald Lee #31112

[Don O'Connell #33101]

Re: Fiberglass vs. Composite Rear Spring

Folks,

Thanks for all the responses. I'll be looking into the heat shields since the Vette Brakes instructions are very specific (i.e. recommended in all applications and "DAMAGE FROM EXCESSIVE HEAT WILL VOID WARRANTY" - guess somebody must have melted one and wanted a replacement under warranty).

With my worn spring I've only got about 1 1/2" exhaust clearance and I'm assuming (and I know what that can get me) that I'll get a little more clearance with the new spring.

So, off to get just one more part......

Don

P.S. Joe - I finally did track down the Timkin front and rear bearings (thanks).

[Bill D.]

Re:Heat shield

Koolmat is the company that designed the heat shield for Vette Brakes.VB does not offer it because of cost and demand.Many users decide to make thier own.The phone number I posted is no longer used,sorry!You can get a lot of info @ thier website below.

http://www.koolmat.com

[Don O'Connell #33101]

Re:Heat shield

Thanks Bill. I was just searching for them! Timing is everything.

Don

[Duke W.]

Re: Fiberglass vs. Composite Rear Spring

I don't have any experience with KYB, but I do with Bilsteins which are the original deCarbon shocks. It's an excellent design, but the damping rates are fixed. So if the manufacturer doesn't set them up to your taste, you're out of luck. Most run of the mill replacement shocks have insufficient rebound damping in my opinion, but it helps the ride. I assume you have the KYB Gas-A-Just which are supposed to be for sporty cars, and should have more rebound than than a "ride" shock. I think you need some input from other KYB users. An older KYB catalog I have lists the p/n for the Gas-A-Just as KG4514 (F) and KG 5501 (R) for all 63-82. They also list numbers for the GR-2 low pressure gas shocks. Hope you didn't buy those. They're a ride oriented shock and probably have insufficient rebound damping for a sports car.

I've recently become a fan of Spax shocks. They have 14 position adjustable rebound damping, and you can adjust them with the shocks on the car. I replaced the Bilsteins on my Cosworth Vega and was able to tune out an over rebound damping situation in the rear and insufficient situation in the front. One of the Bilsteins had gone bad so I took them down to Bilstein North America on a trip to San Diego. I presented them along with my 1979 purchase receipt, and they honored the "lifetime warranty" and rebuilt all four shocks. Now that's what I call customer service.

Don't know if Spax has a shock for C2/C3 Corvettes. They used to for the H-body, but they were out of production. Our Club did a co-op deal through Hutton Motor Engineering in Tennessee, and had 25 sets made special order for $250 a set, which is a steal considering the quality and tunability of the shock.

Duke

[Peter Rastello (33299)]

Re: Fiberglass vs. Composite Rear Spring

Don, I just got through reading most of the responsses to your post and am kind of surprised no one mentioned Gary Beaupre's article in the last restorer in which he mentioned the spring rate for a '69 is around 140 lbs/in (as I recall). He mentioned that most spring sources incorrectly listed the spring rate around 315 lbs/in. I'd be interested in hearing some opinions on that.

Pete.