Rebound Only Shocks

[David C.]

One of the Corvette repro suppliers advertises a rebound only repro shock for C2 and C3 which is supposed to be correct in function, as opposed to modern gas shock replacements which act both on compression and rebound. Is there anything to this?

[Paul O.]

Re: Rebound Only Shocks

David

Last year I was at a local chapters monthly meeting with a guest speaker. He was a retired engineer from the Delco-Moraine Shock division. He even commented on that ad in the driveline. That Delco never made a shock for GM's regular production that was rebound only.

[Dan P.]

Re: Rebound Only Shocks

I have rebuilt many original shocks .They were not like that . Delco did make a 90/10 drag shocks for Drag Master but that was to hold the front end up to transfer weight to the back wheels. If you peel there sticker of the Delco number is underneath . But these were not made for production cars.

[Duke W.]

Re: Rebound Only Shocks

90/10 drag racing shocks have very little rebound damping, but lot's in jounce. That's what keeps the front end up for best rear weight transfer. Such a shock would be a very poor choice for road use.

I've never heard of zero jounce shocks. As a general rule rebound damping should be greater than jounce in order to control body motion on rebound, and that's why I like rebound adjustable shocks like Spax and QA-1.

I have a test road not far from my house that has water drain channels across the road. Most people slow down to 15 MPH to traverse these drain channels, but typical production cars still exhibit excess rebound.

My test it to hit them at the 35 MPH speed limit, and if the body rebounds to greater than normal ride height I dial in more rebound damping. This makes for a somewhat firm ride, but body motion is very well controlled, and that's the way I like it. The only car I've ever owned that passed this test with OE shocks is my '88 Mercedes 190E 2.6 five-speed. Mercedes engineers back than really know how to setup a road car suspension - relative soft spring rates, lots of travel, and very well thought out damping rates.

I recall a Bob Riley magazine interview where he said that 90 percent of setting up a race car is shock tuning, and I contend that the same applies to a road car if you want to optimize the ride/handling tradeoff to your preference. In case you don't recognize the name, Bob is one of North America's premier race car designers.

Typical American performance cars of the era were "oversprung and undershocked". The oversprung (too stiff) part does not apply to the C2/3 base suspension, but the OE shocks are still too soft, especially in rebound.

Duke

[Tom B.]

Re: Rebound Only Shocks

I also read that ad for the restored original 10/90 (not 90/10) shocks with great interest as I was getting ready to replace the original shocks on my wife's '81. The left rear was leaking. I know they are original because she ordered this car new and I'm the only one that works on it except for alignments. Here's what I found. All four shocks compressed very easily and were very resistant to rebound. I have no way to tell if the compression (jounce) was actually only 10% but it isn't far off. I have some other nos Delco standard replacement shocks here I bought for something back then and never used and they have a much stronger jounce than the Corvette ones. The vendor claims C2/C3 Corvettes were designed to use these 10/90 shocks and modern gas shocks will not allow the suspension to work as intended. I believe that if GM had nitrtogen charged shock techology back then they would have surely used it on the Corvette.

Anyway, I put on the currantly available Delco gas charged shocks listed for a C3. I haven't driven it yet as I'm doing some other chassis cleanup so I can't give any before/after review yet.

Tom

[Don S.]

Re: Rebound Only Shocks

I'm a retired Monroe Shock employee and naturally prejudiced toward Monroe's. Have them on my 65 and they ride much better that the KYB's that I removed. Unless your going racing the Monroe units that you can buy at most Auto Parts stores are more that adequate. If you want to jar your fillings (or dentures) loose go with the exotic imports: KYB, Bilstien, Koni etc. Adjustable shocks are a waste for street driving and cruising as they only affect suspension control at high speed and load.

I can assure you that there is no way to determine the condition of a shock with out it being installed on a vehicle. The one exception is if it is completely worn out with zero resistance in either direction. We used very sophisticated test equipment (shock dyno) to determine control values. You physically cannot generate enough speed or force by hand to activate the valve stack. On most applications the shock is controlling the rebound of a spring that has hundreds of pounds load carrying capability. The spring will tend to control its self on compression.

The best shock test is on the car and is the tried and true bounce test. Get the bumper moving rapidly up and down and then release it. The bumper should move no more than 1 and half cycles before coming to rest.

OE shocks back then were designed to enhance comfort at the expense of handling. Most aftermarket replacement shocks were designed with a better balance between comfort and handling. There was always control built into compression and rebound and it was never 90/10 unless they were drag shocks.

[Duke W.]

Re: Rebound Only Shocks

Adjustable shocks are a waste for street driving and cruising as they only affect suspension control at high speed and load.

A few of us still like to drive our vintage sports cars/sport sedans in a sporting manner like attacking twisty canyon roads that aren't always very smooth or even an occasional track event. Starting with sticky tires, adjustable rebound shocks along with alignment tuning and maybe different anti-roll bars are the parts and tasks required to dial in the handling. The Corvette base suspension wheel rates (about 80 lb/in, front, and 140, rear for small blocks) are just fine and provide decent ride quality even with more rebound damping than OE.

Duke

[Dan P.]

Re: Rebound Only Shocks

I have had hundreds of NOS Delco shocks . NONE were 90/10 shocks . Some are softer on compression . But never 90/10 .

[Edward J.]

Re: Rebound Only Shocks

I agree with Don, The factory shocks tend to have resistance more one way that the other , percentage wise cannot tell you. I feel the older vintage shocks tend to have a little better ride feel and may not handle as good as the gas charged shocks of today.

[James B.]

Re: Rebound Only Shocks

I also read that ad for the restored original 10/90 (not 90/10) shocks with great interest as I was getting ready to replace the original shocks on my wife's '81. The left rear was leaking. I know they are original because she ordered this car new and I'm the only one that works on it except for alignments. Here's what I found. All four shocks compressed very easily and were very resistant to rebound. I have no way to tell if the compression (jounce) was actually only 10% but it isn't far off. I have some other nos Delco standard replacement shocks here I bought for something back then and never used and they have a much stronger jounce than the Corvette ones. The vendor claims C2/C3 Corvettes were designed to use these 10/90 shocks and modern gas shocks will not allow the suspension to work as intended. I believe that if GM had nitrtogen charged shock techology back then they would have surely used it on the Corvette.

Anyway, I put on the currantly available Delco gas charged shocks listed for a C3. I haven't driven it yet as I'm doing some other chassis cleanup so I can't give any before/after review yet.

Tom

Tom,

I'm looking forward to reading your upcoming review.

James