Cocktail Shakers: Maybe on a Cadillac or Rolls-Royce, but a Camaro?

Despite the known dangers of putting ethanol in your own tank before driving—as opposed to putting it in your car’s gas tank—there have been some official associations between alcohol and automobiles. The 1957 Cadillac Eldorado Brougham came with a custom minibar in the glovebox. If you have the means to own a Rolls-Royce Ghost, you can order it with a “Coolbox” installed at the Goodwood works that keeps the bubbly chilled (for backseat passengers only, one presumes) and has dedicated storage for a couple of champagne flutes.

You might think, then, that when vintage Camaro enthusiasts talk about “Cocktail Shakers” in their convertibles, they might be discussing something similar, but in this case the term has nothing to do with the fruit of the vine or its grain-based cousins in the EtOH family. It has to do with how Detroit automakers did a clever bit of “engineering by afterthought.”

Most of us probably think of our car’s roof as being there to protect us from the elements, but the roof is a structural element. Removing the roof to make a convertible (or cutting a big hole in the back of the body to make a hatchback) decreases the body’s overall stiffness. That’s obviously an issue when a vehicle uses monocoque or unibody construction, but even convertibles with body-on-frame designs can exhibit symptoms of their bodies flexing like cowl shake. Every structure has one or more resonant frequencies. Those resonances can create an oscillating feedback loop that results in vibrations that the driver and passenger can feel.

During the development of the first-generation Camaro’s convertible iteration, when then recently-installed Chevrolet General Manager Pete Estes was given a ride in an early prototype at the General Motors Proving Grounds near Milford, Michigan, the new boss found the vibrations to be unacceptable for a production vehicle. Estes tasked his engineers with immediately finding a solution.

Normally, the solution would be to make the mid-section of the body less flexible, but while conventional methods like reinforcing rocker panels and stiffening the floor ameliorated the shaking, it didn’t completely solve the problem. Eventually, Estes’ team came up with something that had earlier been used on Chevy’s own Corvair, similar to how Ford engineers had addressed the torsional vibration of the early-1960s Ford Thunderbird and Lincoln Continental convertibles (which shared a platform). Rather than address the bodies’ flexibility, the engineers attacked the vibrations. Since the vibrations were the result of resonant frequencies, they realized that if they could effectively dampen those frequencies, they could not cause the vibrations. In the case of the Conti, Ford engineers mounted weights on the end of what are essentially leaf springs in each corner of the car’s body. The assembly is acoustically tuned to the body’s resonant frequency, and when the body is subjected to loading, the energy from that loading, which would normally start the feedback loop of oscillations, is instead absorbed by the damper.

The early-’60s Continental and T-Bird are large cars, with substantial body overhangs front and rear, so there’s no problem fitting in and hiding the relatively long mechanical dampers. Corvairs and Camaros, though, are relatively compact, so for the redesigned 1965 Corvair convertible, Chevy engineers put a weight on a coil spring inside a sealed cylinder filled with automatic transmission fluid, all tuned to the body’s resonant frequency. The sprung weight would dampen the body’s vibrations while the ATF would dampen the motion of the weights. The motion of the weight inside the cylinder is not unlike the contents of a cocktail shaker, hence the nickname. The capsule ended up being small enough to be tucked vertically in the corners of the body.

At the next demonstration of the Camaro convertible, when engineers took their boss for a ride, Estes was very pleased with the lack of vibration. He wasn’t as happy when he found out about the solution. Not only was he reported to be vocally disappointed in what he considered to be an inelegant, albeit clever, solution, the four canisters added about 100 lbs to the weight of what was supposed to be a sporting automobile. Estes tasked the engineers with coming up with a better solution, but they were never able to replace the Cocktail Shakers before the convertible Camaros were discontinued when the second-gen Chevy pony car was introduced as a mid-year 1970 model.

While you may be able to buy a complete, new reproduction convertible body for your first-generation Camaro, sourcing the Cocktail Shakers might be a bit more difficult, as they are long since out of production and nobody appears to be manufacturing repro units. GM made about 60,000 first-gen Camaro ragtops, so used dampers can be found, though they are getting rarer.

Installing used units shouldn’t be a problem, as it is a very simple mechanical device, and the only things that can go wrong are a broken spring or leakage of the ATF. They’re also not prohibitively expensive. Advertised prices are between $125 and $500 each (try Camaro Central and Heartbeat City).