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67 289 engine vibration

6925 Views 16 Replies 6 Participants Last post by  Dboxman7
On the freeway most noticeably above 60 mph, when on even flat road if I let off the gas, no problem, but when I give just enough to maintain speed I get a heavy vibration/shaking feel from the engine. Not violent like something is breaking, just too heavy to feel right. Doesn't do it when accelerating or when I let off the gas. I haven't started to try to diagnose yet... maybe vacuum advance? or ignition/timing?

Any thoughts or help appreciated!
1 - 1 of 17 Posts
Wheel balance (shake)? Bad pinion angle will cause a vibration under load. Also check slip yoke bushing in the tail shaft. Move the slip yoke up & down to check for excessive play. I've seen a bad bushing cause a vibration under load. Oh yea prop balance too.
1 - 1 of 17 Posts
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