67 Fiberglass Rear sring

[Roy Braatz]

I've had my 67 for 20-plus years a coup, 327-350HP four speed and thinking of replaceing the rear spring with the new Fiber one. First which one 330lb or 360lb.? and has any one been realy happy with the exchange on ride or what ever?
Thanks ROY

[Mike S.]

Re: 67 Fiberglass Rear sring

The 360# spring is recommended for big block cars. I believe VBP would suggest the 330# for a small block and most types of driving.

You can reach VBP at 800-237-9991 or VBandP.com.

[Duke W.]

Re: 67 Fiberglass Rear sring

330 pounds/inch is double the fixed rate '63 spring. Yours is variable but averages about 160 lb/in.

Rather than buying a new spring, why not just overhaul the original spring. As long as it has not lost signficant material due to corrosion, it is probably okay and a good anti-corroison coating, new liners, and new spring link cushions should make it nearly like new.

Duie

[Wayne W.]

Re: 67 Fiberglass Rear sring

And if you use that fiberglass spring you will notice considerable rear end bounce.So get some very good rear shocks, or you will be dissapointed with the ride.

[Nick Vigorito]

Re: 67 Fiberglass Rear sring

I have a fiberglass rear spring on my 67 SB. It was there when I bought it so I don't know the rate. It is probably a 300 or a 330 lb. I have KYB gas shocks and I do get considerable bounce in the rear at times over larger bumps or uneven pavement. If you are traveling fast enough I can even see it making conditions dangerous. Outside of the bouncing the ride is pretty good. What is the ride like if I go back to the original type steel leaf spring? Should I be using a different shock?

Thanks!

Nick

[Duke W.]

Re: 67 Fiberglass Rear sring

A couple of thoughts regarding damping. First, the stiffer the spring the more rebound damping authority is required to control body bounce. Second, all springs have an inherent damping rate and the OEM multileaf steel spring has higher internal damping than a single leaf composite spring, and even for the same rate, a composite spring will likely require more rebound damping authority although damping is a subjective parameter, and there are no magic formulas to determine ideal damping rates.

Your best bet on shocks is always to buy adjustable shocks like Koni or Spax, so you can dial in the amount of damping that is suitable for your specific spring rates and driving conditions.

Duke

[Roy Braatz]

Re: 67 Fiberglass Rear sring

nick I have little or no bouncing and I do have gas shocks, its just that it rides a little hard and thought may be a fibber spring would ride better, but I dont wont it to bounc all over the place.

[Grant M.]

Re: 67 Fiberglass Rear sring

Vette Brakes sells a specially-valved KYB rear shock specifically recommended for use with the composite spring. We installed a composite (with the KYBs) on our 78 and are very pleased with the ride/handling. On the other hand, we have a new 7 leaf rear spring on our small block 65 (with newer GM shocks)and I can't say that the ride/handling on that car is all that harsh. The stiffer spring does make me think that a rear sway bar (not stock for 65) would help control what seems to be oversteer in cornering.

[Duke W.]

Re: 67 Fiberglass Rear sring

If you combined the HD seven leaf spring with the base variable rate front springs, THAT is why your car oversteers. Installing a rear anti-roll bar in the rear will make it oversteer even more.

If your car has base front springs and the HD rear spring, you can either replace the rear spring with the correct nine-leaf base rear spring or increase the size of the front anti-roll bar to reduce the oversteer bias.

If you increase rear roll stiffness either with stiffer springs or a larger anti-roll bar, or installing a bar where there was none before the car will be biased toward less understeer/more oversteer.

Increasing front spring or bar rate will increase understeer/decrease oversteer.

Duke

[Nick Vigorito]

Re: 67 Fiberglass Rear sring

Thanks Duke.

Given that I need to get shocks with more damping than the KYBs to go with the fiberglass spring on my 67 SB, do you know if you can adjust the Koni's or Spax to have more damping than the non-adjustable KYBs I have now? Anyone have any experience with QA1 adjustable shocks that I see advertised in the Corvette Magazines? I don't know anything about any of these shocks. I assume they all can be adjusted while on the car?? Perhaps I should just check out those special KYBs sold by Vette Brakes...

Nick

[Duke W.]

Re: 67 Fiberglass Rear sring

I've never personally compared the shocks you mention, but I would suspect that the the stiffest setting on Konis or Spax would be stiffer than the KYBs.

The Konis must be removed to adjust. The Spax can be adjusted on the car.

Duke