65 mph HARD shake

Yes, I know that everyone and their dog has reported this problem, but I'm starting to think that mine might be a little worse. I've got a '99 Miata I purchased back in July, and it has always had the 65 mph shake. I had new tires put on and asked them to take extra care when balancing the wheels. This seemed to make the shake all but completely go away. Over the past 6 months the shake has returned and gotten worse. I examined my tires and they were shot, looked as though the alignment was out. So I had the car aligned (which was severely out of adjustment as it turns out), then purchased new tires again last week. The shake has not gone away, in fact it feels like it is still getting worse...

It starts at around 58-59 mph and can go up as high as 75+ mph depending on what mood it is in. It is a hard shake, I feel it all over the car, seat, steering wheel, dash, mirrors shake, I can see the hood shaking relative to the road, and the entire inside of the car is rattling (the top hinges, stuff in glove box, basically anything that isn't welded). Not sure where to go from here, the guy I had align it said that none of the suspension/steering parts appeared to be broken or too worn, they were just badly misaligned. All tires are sitting at

29psi.

Any ideas?

-Tim

Reply to
twistednerve
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Forgot to mention, this car has about 123,000 miles on it. So even though the alignment guy said everything appeared fine, I supposed it is possible that some parts could be worn, just not sure where to start.

Thanks,

-Tim

Reply to
twistednerve

My car had this problem, too. I installed a shock tower brace and it helped immensely. I even put a cheap one that I got off Ebay on. I am sure you will get a lot of people saying that shock tower braces on a Miata don't help but I feel that this mod made my car a lot less loosey goosey in the front.

Reply to
DBLZOOM

I think that the strut tower braces help, even the cheap ones, at least to some degree.

This problem being described, however, is more than simple cowl shake. It sounds like he has a bent and/or badly balanced wheel, but they have been balanced more than once and they have not told him anything is wrong. Unless the shop is incompetent, I would start looking at other parts of the front suspension like the hubs, a-arm bushings, shock mountings, etc.

It might help to take it to a new tire shop or mechanic anyway.

Pat

Reply to
pws

I would agree that a bent wheel or some such problem is very likely, do you have access to a spare set of wheels and tires or a friend with a miata who'll allow you to investigate this? It'd be easy to do at home, swapping out all 4, if the problem goes away you might even be able to figure out which one / ones have the problem by doing a quick test drive in between swapping each tire back onto the car.

Chris

99BBB
Reply to
Chris D'Agnolo

My '91 had the worst shimmy I've ever seen when I bought it last year. It had 90k on it and original shocks. I put Bilsteins and Yoko tires on it and the shimmy was gone. I didn't do anything else at the time (I didn't even have the chasis braces in yet). when I put my Blizzaks and steelies on the winter there was a light shimmy at 65 +/- 3 mph, but nothing as bad as the shot shocks. Makes me thinnk this is why Mazda started putting Bilsteins on at the factory.

Reply to
jeff.remson

That is good idea. I actually do have a friend across the street with a '93 Miata and I bet he'd be willing to let me try his wheels. Hopefully they will fit. I don't mind spending the money to fix it, but I'm a tightwad by nature and hate the idea of throwing 100's of $'s in a direction without knowing if it is going to fix the problem. It'd be nice if there were a way to try and diagnose w/o dumping a bunch of money into new rims or suspension parts that I may not need.

This is a good step in the right direction, thanks.

-tim

Reply to
twistednerve

That is a good idea by Chris.

Unless you've got extra-large rotors, the wheels from your neighbor's '93 miata will fit.

You can actually do two wheels at a time, because the miata is so easy to lift one entire side up rather than one corner at a time, but if it cures the problem, then as Chris suggested, you will want to switch them back one at a time to find the problem wheel.

Be careful doing hard starts if you have 2 different types of tires on the back while you are investigating the problem. That rear end can get very *squirmy* depending on the difference in tires.

Good luck,

Pat

Reply to
pws

Jeff might have a good point on the shocks if they're high mileage but I'm with Tim, no / low cost repairs are the best. The miata can be so picky about wheel balancing some people say that you have to go to the place that has the really state of the art machine. You can find lots of info on miata.net .

Keep us posted, Chris

99BBB
Reply to
Chris D'Agnolo

On Thu, 13 Apr 2006 12:46:48 GMT, snipped-for-privacy@yahoo.com wrote in news: snipped-for-privacy@e56g2000cwe.googlegroups.com:

Last time I bought new tires the installer did what was supposed to be a high precision balancing. But he was using weights that weren't very close in value to what was indicated. I tried to impress on him that it needed to be done to a much higher tolerance. But he insisted this was fine. It wasn't, and the shimmy was quite severe.

I went to a shop with a better reputation to have them rebalanced. Even they tried to laugh at me when I told them that they needed to use the smallest weights they had, trying to tell me that it wasn't such a big deal. I insisted, and the shimmy went away.

I would try to find another set of Miata wheels as suggested elsewhere and verify that a good balanced set makes your problems disappear. If the other wheels are just as bad, then you know you have other problems.

If it was the wheel, find a shop that takes you seriously.

Reply to
Red

The problem can hardly be shocks or other non rotating parts. It has to rotate with the wheels to appear in the shimmy range. A bent wheel and an incompetent shop* sounds the most likely to me, but it could be tires or brake disks, or smaller parts too. Though shocks and braces might well be able to mask the problem a bit.

Leon

  • Or a shop that thinks nothing of a wheel that is "just a bit" out of round, unaware of the sensitivity of the Miata. Which is not very competent anyway in my book.
Reply to
Leon van Dommelen

The leading causes are: TIRES- Out of balance, out of true, damaged, etc. Rims- Out of true or mismounted to hub. Wheels may be out of balance as well. Given a choice, I'd prefer to check and balance them (with valce stems installed) before new tires are mounted. Stick on weights are ideal for this, since they may need to be changed as part of tire balance. Bad Alignment will damage the tires, but of itself should not cause the "shake". Having said that - If the tires shimmy, and cup, due to misalignment and/or play, you will eventually get vibration.

A load force balance using a Hunter 9700 or equivalent by someone who KNOWS HOW to use it will allow a balance that makes the best of an existing situation, or (hopefully) identify the offending tire/wheel combination. Tires that "flat spot" when sitting are more difficult to deal with, and should ideally be checked after they are warmed up.

My average is about one out of five NEW aftermarket replacement tires require a load balance, or replacement due to ride disturbance. A new tire that load balances may not do so after several thousand miles. If a new tire requires an excessive amount of weight, reject it. Especially if it is not typical of the other three new tires.

Basically: Check each rim for run out and out of round. Checking the rotors for run out is also a good idea. Check each new tire for the same after it's mounted on a known good rim. Tread patterns that "visibly wobble" are also cause for tire rejection.

Some people advise driving the car long enough to warm up the tires before they have weights added. There is an additional opinion concerning "new" new tires and new tires from stock that are at least several months old. Sale tires tend to fall into the really new stock or really old stock categories.

Check static balance first. Rotate the tire on the rim for best static balance. Dynamic balance. Is the amount of weight needed more on one tire than the others? If the additional weight is around twice typical, the tire rim combination is suspect. Load balance - If a tire rim combination behaves poorly, and the rim is true, the tire is bad.

Shocks and braces can improve a bad situation, but will not cure it.

Making sure that you get good tires may not endear you to the tire dealer.

Occasionally, a bad rotor (warped, poorly balanced, etc.) will contribute to the problem, as will play in the suspension.

Reply to
Chuck

Grag the top of the wheels and push them in and out. Grab the sides and push and pull them. if you find any play in them, one of the ball joints on the susmpension or steering arms may be bad. you may also have a craked suspension arm bushing that does not start to act up until you get it up to speed and the tire thread starts to vibrate the worm part at the right frequency.. You may also have an out of round brake rotor but that is less likely.

Reply to
M. Cantera

Wow, a phenomenal amount of information here. Thanks a ton everyone. I was talking to my neighbor this weekend. He's a Mazda mechanic and a good guy, which is exactly why I DON'T go to him with every problem I've got, but he breached the topic so I felt obligated to describe to him my plight. Long story short, he's agreeing with the bent rim/out of balance theory and asked me to put the car up on stands and pull all the wheels off. He's going to take them to the shop he works for and put them on what sounds like a pretty high precision machine to check the balance and trueness of the rims/tires. He also happens to be the same neighbor who has the '93 Miata, and takes very good care of it. Hopefully this will provide an answer.

After fixing this this issue, I am going to replace the shocks and maybe install some shock towers, enough people seem to report positive results from doing this.

Thanks again for all the information, I've saved it off for use later if this doesn't get it.

-Tim

Reply to
twistednerve

Please let us know which Shock towers you get.

Thanks,

- Pat

Reply to
Pat Dreiding

Tim, I had a 99 Miata a while ago and never had any shake that you described. Why is the important, you ask? Well, the car I purchased (used) had aftermarket wheels and tires. Hope this helps you solve the problem. Cheers! Squat

Reply to
Squat

you're Evil Pat! Or was it Pat Evil?

Chris

99BBB
Reply to
Chris D'Agnolo

I want to see a miata.net Garage tutorial on changing shock towers.

Reply to
Lanny Chambers

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