Piston Slap: Flexin’ the Corvair’s frame?

Tito writes:

Hi Sajeev, I wrote to you a long time ago at another blog in a galaxy far, far way asking which car my mom should buy after totaling her old Scion. The eventual answer ended up being “nothing” for many years. I basically forced her to stop dilly dallying and buy something, so she bought a new Kia Forte because it was cheap and had all the bells and whistles she wanted. Anyway, since you asked for more Piston Slap, I’ve got a classic car query for you.

I have a ’65 Chevy Corvair Monza convertible. It’s been upgraded to look like a Corsa model. I bought it just under five years ago and since buying it, I’ve rebuilt the engine (four-carb, 140-horse engine with a little extra cam and electronic ignition), rebuilt the rear suspension, rebuilt the shifter, replaced the differential, and done various other smaller projects. There’s always something to spend money on! The front suspension was rebuilt shortly before I bought it. All in all, the car is now a tight, well-sorted driver (see attached pic cruising through the redwoods in California).

Here’s the question: While second-generation Corvair convertibles are known not to be as stiff as first-generation ones, this car has never felt overly willowy. However, in the last few weeks (I’m not driving as much because of the pandemic), I’ve noticed that the car feels distinctly more flexible, which seems more apparent in the cowl area. It’s not classic cowl shake you get from going across railroad tracks and the like, but a lower frequency looseness. I haven’t had a chance to get under the car to inspect the suspension, since I just finished moving. Hoping to do that soon.

But what would cause a sudden change in how the car feels structurally? Besides doing a visual inspection on the suspension, what else should I check? I should mention that this car does not have any obvious rust on it besides a little bubbling under the paint in the doors. Thanks, Sajeev!

Sajeev answers:

No, thank you for keeping the Piston Slap flame alive all these years!

The Corvair was the first unibody vehicle made by General Motors/Fisher Body, but chassis integrity never came into question. (The same can’t be said for Ford’s first foray into unitized design, the massive 1958 Lincoln.) Unless this has been a non-beach-going California car all its life, rust is always a concern: Get a smartphone endoscope, run it behind the dashboard/below the windshield and look at every corner of the cowl.

Odds are the chassis is fine, but I am no Corvair expert. Luckily, Hagerty’s Mr. Kyle Smith is. He suggests the following:

“The front suspension is only held to the uni-body with six bolts. But with no clunk or rattle stated, I wouldn’t think any of those to be loose. The strut rod bushings would be my first check, as these set the caster of the front end and are rubber bushed at the chassis connection towards the rear of the wheel well.”

Kyle’s comment about strut rod bushings sounds spot on: Speaking from personal experience, a recently installed (2–3-week old) strut rod bushing failed on my 1995 Lincoln Mark VIII due to an installation/manufacturing mishap. The bushing let go under moderate braking forces; apparently, the nose dive was enough to pop the bushing out. Most likely, your issue (if applicable) isn’t that bad, but it’s still a good place to start.

To this day I still don’t know why that bushing failed happened. Since my daily driver needs to be fully sorted (old cars masquerading as new ones!), I threw away both sets of (firmer but supposedly still rubber) high-end strut-rod bushings, replacing them with cheaper and definitely rubber replacements, and everything tightened back up to perfection once more.

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