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Hey guys,

I'm hoping some of you can chime in on diagnosing what may be going on with my 99' Miata. At about 62mph a heavy vibration starts (the whole car) not so much in the steering wheel but mostly under my seat. The dash vibrates and makes noise when it happens. The car stops vibrating after 75mph.

-I already changed out a suspected wheel bearing, that didn't solve the issue.
-I already changed the engine mounts, that didn't solve the issue.
-I got my tires re-balanced twice at discount tire, that didn't solve the issue.

The only thing left I can think of is perhaps a harmonic balancer? Diff or axles?

One weird thing I noticed is, I don't remember the heavy vibrations before installing my flyin miata clutch and lightened flywheel. I'm pretty darn sure I did everything correctly and it drives quite amazingly with the new cutch and flywheel.

Thanks for any opinions or suggestions.
 

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They do that... It has something to do with the harmonics of the car.

Google 65mph shimmy and you will find a good bit of information on it and things that people have done to limit it.
 

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You can't handle all of my brown.
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163 Posts
I've had a driveshaft bolt come loose and fall out. Made a vibration at highway speed that was at a higher frequency than the normal 65 shimmy.
 

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You might even check out the motor mounts.
 
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