It is an incontrovertible fact that the first generation Camaro and Firebird were among the most beautiful cars ever built by General Motors. They were available as coupes, or, for a few dollars more, you could buy one with a folding top. Unbeknown to the buyers of the convertible, four “cocktail shakers” were included at no extra cost. They were there for a very good reason.
When Chevrolet engineers drove an early prototype of one of the convertibles around the test track at the GM Proving Grounds, they found that the car suffered from more “cowl shake” than they’d like, indicating that the roofless body was too flexible. I’ve included an image below of a reproduction body shell made by Dynacorn International for a ’67 Firebird so you can see that there’s not much steel between the bow and the stern of this car when there’s no roof.
One solution would have been to further reinforce the rocker panels and stiffen the floor, but this would have added weight and cost. Someone remembered that the second generation Corvair convertible introduced in 1965 also had a problem with cowl shake, which had been remedied by adding dampeners to each corner of the car. These dampeners were steel cans, each containing a heavy weight mounted on springs. The idea was that these devices could be tuned to counteract the harmonic vibrations or resonant frequency of an overly-flexible body.
The Chevy engineers bolted four dampeners in their Camaro prototype and were satisfied by their efficacy.
The dampeners, known as “cocktail shakers,” were filled with automatic transmission fluid on the assembly line. Decades later the devices have proven to be reliable; their only problems are caused by rust or springs that get weaker over time. There’s a market for used shakers, which have unique part numbers for Pontiacs vs. Chevrolets, front vs. rear, left vs. right, and model years 1967-1968 vs. 1969. The difference is usually in the mounting bracket.
Chevrolet General Manager Pete Estes, who’d been alarmed by a Camaro convertible’s cowl shake in an early test drive, was delighted by the improvement his engineers made for the later prototype – until he learned how they’d accomplished it. He was not amused by the hundred pounds of weight added to each car by four shakers, but it was too late to design and implement another solution.
I could not find a photo of a shaker mounted in the engine compartment of a Camaro, as they’re hidden by lots of stuff. However, you can clearly see the front-mounted shaker above the spare drive belts in this Corvair, as its engine seems to have been installed in the rear of the car for some reason.
About 110,000 Camaro and Firebird convertibles were built for the 1967-1969 model years. 1970 Camaros and Firebirds were not equipped with cocktail shakers for the simple reason that GM didn’t build convertible versions of the second generation cars.
Chevrolet next built a Camaro convertible in 1994, and there was a Firebird twin in that year, too. The new convertibles were shaker-less; they relied on a strengthened chassis to reduce cowl shake.
Sooo, these were all “shaken, not stirred?” I’ll see myself out now, LOL!! 🙂
Packard used a similar idea (“harmonic front end stabilizer”) in its V-12 models in the early Thirties, but they were mounted on the ends of the front bumper, later adding them to the rear bumper as well. They went away for 1937 after the introduction of independent front suspension (and some frame modifications.)
I think Lincoln also used a version of these in the four-door convertibles from 1961 on,
A typical stupid GM half-azz kludge. Instead of proper body design they resorted to reducing shake by this kind of band-aid idiocy. I had a ’68 Firebird 400 convert w/ Hurst 4 Spd, loved the car (it was a real ticket-getter!), but I was aware of these cocktail shakers that to me represented short-cut engineering, all too common at GM.
Maybe a band-aid, or maybe clever engineering. I agree a properly designed stiff body/chassis would be best, but in those days before computer-aided engineering, it wasn’t that easy. And who knows, adding the proper stiffness into the stampings may have added more weight or dimension in places where it would get in the way of other functions. Now the extra mass ‘vibration absorber” (not strictly a damper) bolted to the transmission of some Vega’s in a vain attempt to reduce NVH was definitely a band-aid.
I dunno, I’d call it lazy engineering. Nash somehow built a properly stiff unit body starting in the ’50s, even the ’53 Rambler Custom Convertible, though it did have side window frames.
At least Packard’s answer of chrome cylinders curled into the bumper ends looked kinda cool.
My 2 ’56 Packards didn’t need those though.
Chrysler used computer aided design for their 1960 switch to unibodies. While it was nothing as sophisticated as CATIA, it was based on computer design experience gained from their rocket design process.
GM also had an early computer design system called DAC-1 ready around 1964 they developed with IBM. Theoretically considering a three year design cycle that may have been available for use on the Camero / firebird chassis.
GM also owned Saab when Saab had cowl fracturing issues during the late 90s-early 00s. Maybe computers wouldn’t have helped them too much…
Yeah, there are definitely convertibles where the added chassis bracing adds over 100 lbs. I would have been annoyed as Estes was, because it seems like a kludge, but it’s not like those convertibles belonged on a track.
Also, I am nearly certain I’ve seen third-gen F-body convertibles, but maybe someone like ASC built them.
Then Mercedes engineers were “stupid” too – the vaunted W124 convertibles have similar vibration dampers….
Yep, they added weight and cost without actually improving the structure of the car. Makes perfect (non)sense!
The 1982 Camaro I test drove for a co-worker of my mom’s, who was thinking about buying it, HAD a fixed roof, and the cowl shake was so bad at 75mph the inside mirror was so blurry it was useless, kind of like motorcycle mirrors used to be before they counterweighted the head. I knew right then those would never be on my radar screen, besides the fact they are butt ugly.
Amazing. Somehow, I’ve never heard of these. Never owned a 67-69 Camaro/Firebird Convertible either, so maybe that’s why.
I’m surprised at the interesting ‘fixes’ that they used to correct/ Band-Aid an issue. And for as little money/time as possible.
Porsches and TR7s also had harmonic dampers.
So did my BB8 Prelude and that was a tin top.
But I love the cocktail shaker full of ATF – one Hydramatic coming riiiight up, boss.
Hydramatic would actually be a pretty good name for a cocktail at bar with an automotive/Art Deco/Mid Century Modern theme. I’ve always thought an old car dealership showroom from the 30s-60s would make a pretty neat bar.
After a major drivetrain issue with my mother’s 1964 Rambler American, it was replaced by a yellow 1967 Camaro coupe. We’d never been a GM family, but the Camaro (and Corvair from the same year) were beautiful cars – both have aged extremely well.
Interesting that four relatively expensive, and heavy, dampers were added to remedy the problem with the convertibles. This is the same division that decided not to add springs to deal with the first generation Corvair’s potential swing axle issue. Maybe the bean counters were at lunch, or maybe, being 1967, everyone was just high and giggling.
Early Citroën 2CV used similar inertia dampers in place of hydraulic shock absorbers. A different application but using the same principle.
“It is an incontrovertible fact that the first generation Camaro and Firebird were among the most beautiful cars ever built by General Motors”
Wow, a completely subjective opinion and one that really cant be backed up. If one reads the reviews at the time, they were very mixed. There simply was no great love of the new F Bodies. Favorable but hardly gushing. “incontrovertible fact”? Hardly.
These dynamic dampers are still more sophisticated than the lumps of cast iron installed in the front bumpers of early Porsche 911s to cut down on oversteer.
Thanks for a fascinating post! Some MotoGP racing motorcycles have mass dampers; known as lunch boxes,
the contents of which remain unknown; but this might be heading in the right direction (?).
Not exactly my favorite car (along with the Firebird but it is good to see two ‘unmolested’ ones if only in a picture.
Chrysler K-cars used the front bumper as a tuned mass damper- at idle, you could clearly see the bumper vibrate in time with the engine. It worked surprisingly well at smoothing out the 2.2 four.