Congratulations on joining the Miata family!  Get over to
www.miata.net and be prepared to spend *lots* of time there.

The older Miatae are known to have a shimmy at 65 mph.  It's a
combination of things which can be helped with changing the sway
bars, having all four wheels aligned and installing a front shock
brace.  My '90 did it.  I've done all of the above except adding
the shock brace and that's sitting in the garage waiting for a
few spare moments to get installed.

See Lanny's site for alignment specs:
http://www.hummingbirds.net/alignment.html

And be prepared to spend lot of money on sunscreen. ;-D

Iva & Belle.)
'90B Classic Red.)
#3 winkin'  Miata

Lower the tire pressure to 28 psi all the way around and see it that helps.
The one time my 91A had the shimmy was when all 4 tires had very different
tire pressures.

]I just recently acquired the subject Miata, it had has been setting under a
]cover uncranked for 6+- years, after making many minor repairs, the car
]checks out fine with one exception, there is shimmy or bounce around 65 MPH,
]seems to be in the rear. We had to replace the tires which were computer
]balanced when installed, I first thought all they needed was high speed
]balancing , after $50 for the balancing there wasn't any improvement, OK,
]next I replace the shocks thinking this has to be the problem but still no
]improvement , the sensation of a tire being out of balance is still present
]in the rear. The car has only 38000 miles and in a excellent maintained
]condition.
]Has anyone else encountered a similar problem ? I would appreciate any input
]that might helpful in resolving my dilemma.

Do I understand that you replaced all 4 tires after the 6 year
storage?

And that all 4 wheels were then high-speed balanced?

Leon

First thing to do is remount all the wheels, tightening the lugs
progressively in the correct sequence with a torque wrench. If you have
wheel locks, get rid of them.

If the shimmy persists, then either they weren't balanced properly, one
of the new tires is out of round, or you have a bent wheel. The balancer
must be set to its maximum sensitivity. Here's another clue: if the
shop's smallest weights are larger than 1/8 ounce, they aren't equipped
to balance Miata wheels.

While alignment and bracing are good things for other reasons, they
don't affect wheel balance or concentricity, which are the only causes
of shimmy. All the other things will do is shift the resonant frequency
of the chassis, so it shimmies at a different speed.

Frank, I have a '90 with ~160K miles on it, but I've never had a shimmy.

On my OTHER car, however, I get a nice shimmy around 65.

Why?  The frame is bent.

Has the Miata ever been in an accident?

Thanks to all for your help, as a starter I plan to revisit the shop where I
had the high speed balancing done.
Thanks Again,
Frank