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72 Buick Skylark, vibration at 70mph
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jtdaniels55
New User
Oct 25, 2019, 8:24 PM
Post #1 of 2
(1536 views)
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72 Buick Skylark, vibration at 70mph
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Greetings, all. Glad to be a part of the group..
I have a 72 Skylark, restored. 195K miles, about 8K on a rebuilt, 350cu engine, performed by Jasper in Indiana (at the time). Had it since December 1974. I'm attached to it. : )
I have an interesting problem at about 70mph.. The car has a very noticeable vibration at that speed, much like you'd feel with a tire or wheel out of balance. But.. the interesting thing is it's oscillatory.. as I hit about 70,71,72.. and hold that speed, the vibration begins, slowly increasing from nothing, to its maximum value, and then decreases slowly back to hardly noticeable. I'd say the period of the cycle is about 3-4 seconds.. This repeats as long as i hold that speed. I haven't tried it at anything over 75, and there is absolutely no vibration of any kind at 60. In city driving the thing is absolutely perfect. At idle you can't tell it's running. Good acceleration, smooth, solid, crisp shifting.. The vibration doesn't shake your fillings loose; but the hood vibrates noticeably; you can feel it distinctly in the steering wheel. Something's not right. And it's reproducible.. Happens every time..
The engine is basically stock. Jasper did their basic rebuild about 7-9K miles ago. It has a Carter 4bbl and a performance manifold. The transmission is original, has been rebuild a few times. It has some sort of shift kit in it, and I'm not sure exactly how that would play in the discussion, but it's there.. The driveshaft has been replace with a high-performance type, installed by my shop a month ago. It was custom made for this car. ("My shop" is a small group of engineer/mechanic types, they typically work on race cars, and older classic Barrett-Jackson-type cars, and normal people cars too.. I have had enormous success with everything they have done with this car and my other one. So, I'm assuming they're competent.. a fair assessment I believe.) The rear-end gears have been switched from stock 256, to 343, and back to 273, in a 5-year period. (I had a mid-life gear-head crisis and wanted torque..) $5/gal gas forced me to settle for 273. They also replaced the control arms in the back. Tires and wheels are all new, and have been balanced and checked for "ovalness," which led to one tire being warranty-d-out.
I used to drive it all over the US.. Phoenix to Detroit, Phx to SF, Phx to LA.. Before I decided to restore it (and started changing everything), it was rock solid on the freeway all the way to 90. I can't recall exactly when I noticed the vibration which is unfortunate, I know, but I stopped driving freeway miles a while ago, and just didn't drive it much for a few years. I do understand that changing things from stock implies this type of thing happening.. But they got the engine better than it's ever been.. So solutions are probably there.. I'm just concerned that the vibration, which is significant in my mind, might cause some other problem. My guys thought the driveshaft might be "jump-roping" I think was the term, which could cause a problem, so it was changed.. I'm not a mechanic, but I am an engineer, so I can understand the technical stuff, and I like it...
I can't think of anything else to enter here.. I hope there's enough to generate some curiosity.. Any thoughts from anyone is deeply appreciated.. thanks for your kind attention.. : )
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Oct 26, 2019, 12:16 AM
Post #2 of 2
(1513 views)
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Re: 72 Buick Skylark, vibration at 70mph
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Congratulations? You can write as much as I do which is an achievement.
Quote your comments in that novel "> Before I decided to restore it (and started changing everything), it was rock solid on the freeway all the way to 90. <"
See the mistake there? It was fine and you changed everything. This car (knew many new thru scrap heap all were still smooth was the "Buick" idea.) Do note saving fuel wasn't even a thought at all except for a terribly short range of miles you could go on a tank of fuel. Don't even try to fight with that you'll lose with this car.
Quote you again "> $5/gal gas forced me to settle for 273. <"
Why could you possibly be worried about the cost of fuel for a nano second? The original engine which no longer means much nor all the changes was meant to use more pure fuel than you will get now. Lead was the "drug" to boost up octane (rating of octane mind you) to squelch down having to use more real "octane" which would cost way too much.
Enough: That speed with the expected wheels and tires that would fit on this thing now is right where a resonance frequency would and does become a problem. The original car was stuffed full of balancing acts, rubber and metal, CV jointed driveshafts at both ends sometime using U-Joints, a spring loaded centering ball good luck doing that again you know that's long gone with all the changes.
The skinny is you had ONE defective tire and tossed just one? There's the key problem now. You are unlikely to find quality control on products cloned or made now nor the machines that could check it before being used - all done, game over.
The real problem now is how YOU can just put up with it the way it is and still enjoy all those many years of memories? You'll never get rid of that vibration I don't think the quality control is "retro-possible" anymore for a one car fix.
Fond memories - I mean that!
Tom
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