1991 miata shimmy

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. Thanks in advance, Frank

Reply to
J. Frank Freeman
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setting under a

the car

around 65 MPH,

computer

high speed

improvement, OK,

but still no

still present

maintained

appreciate any input

Congratulations on joining the Miata family! Get over to

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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:

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

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

Reply to
Iva

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.

Reply to
Mike

]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

Reply to
Leon van Dommelen

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.

Reply to
Lanny Chambers

On Fri, 21 May 2004 16:24:41 GMT, Lanny Chambers wrote in news: snipped-for-privacy@newssvr24-ext.news.prodigy.com:

[chop]

To reinforce Lanny's point: I had new tires installed a while back and had the shimmy even though I had them 'properly' balanced. I had them try twice with no luck. So I went to another shop and insisted that they be very precise. They even partly sneered when I made them use the smallest weights, implying that I was being ridiculously anal. But the shimmy was gone.

Reply to
Dave Null Sr.

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?

Reply to
Dave Christian

Reply to
J. Frank Freeman

Reply to
J. Frank Freeman

Reply to
J. Frank Freeman

So the first balance was at 38 psi? Anybody know how much the error involved might be?

Some tires have a pronounced stiff spot where the bands are joined, giving a shimmy even when properly balanced.

If the shimmy is not too bad, you could try changing the tire pressure a bit or swap wheels front to rear.

Leon

Reply to
Leon van Dommelen

Reply to
J. Frank Freeman

One last possibility: I had a shimmy in my '91, though it started around 80 or so. Replaced a bent rim and she's smooth to 115, fast as she's been to date.

DonB

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DonB

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J. Frank Freeman

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chuckk

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