STEVE / ALL - - -

I'M NOT SURE THAT ADDING CASTER WILL CORRECT THE "SHIMMY" BUT ADDING 1/2 DEGREE TOE-IN SMOOTHED OUT MY EXCALIBUR BY ABOUT 75%. OF COURSE IT DOESN'T DIVE AS QUICKLY INTO THE TURNS AND HAS A VERY SLIGHT "FEELING" OF FRONT END FLOAT IN THE TIGHT "TWISTIES" NOW BUT THESE ARE BARELY NOTICEABLE.

I REALLY BELIEVE THAT THE PROBLEMS WE ARE ALL EXPERIENCING WITH "SHIMMY" - PARTICULARLY IN THE 60 - 70 MPH RANGE - ARE A RESULT OF VERY MINOR TIRE IMPERFECTIONS AND ARE AN INCONVENIENCE BUT NOT REALLY SERIOUS. THEY APPPEAR TO BE EXACERBATED BY THE FACT THAT OUR CARS ARE VERY LIGHT COMPARED TO THE LOAD CARRYING DESIGN CAPABILITIES OF THE TIRES. ON A HEAVIER CAR THE IMPERFECTIONS WOULD BE LESS NOTICEABLE.

I'M GOING TO FOLLOW THE ADVICE ON JIM C'S POST AND HAVE THE TIRES AND WHEELS "PROPERLY" LOAD BALANCED.

Y'ALL HAVE A REALLY GREAT DAY,

BLACKJACK

My $0.02
Almost all cobras have a solid shaft connecting the steering wheel to the steering rack. The "rag" joint that our daily drivers have help dampen the effects of the front tires. Also as mentioned above we have light cars with big tires so any road or tire imperfections will not be mashed out with weight. Put your tires on a SUV and the shimmy will not be noticable on that vehicle.

I am running 17" Kumhos and I have very little if any shimmy. Maybe the lower profile performance tires are truer than most "S" rated tires?

I had a 1998 Honda Passport(Rodeo with badges) that had this same problem and the only way Honda could correct it was by putting better quality tires on and having them trued(shaving off high spots) and balanced on the car. After that the ride was like a caddy. Before the tire truing and on car balancing it was so bad at times my hands would tingle. The only problem was if you rotated the tires you had to rebalance on the car again. I suspected it was a bad set of rotors so rather than deal with it I traded for a Car. It was a shame as other than the shimmy/vibration it was a great vehicle.

If you are having a problem on your cobra find a shop that does on car balancing and tire truing and you will be suprised how much better it rides. Rotation of tires on a Cobra is not a option anyway.

OK, I’ve got to share this with you guys and gals. My EM also has a slight shake at 60 to 65 MPH. While I am determined to smooth it out, it doesn’t have to be perfect but smoother. This weekend, I get under the car and find two worn out stabilizer bar bushings and a loose strut rod bushing. Replace the bushings and tighten the strut rod. Now it’s more prevalent!

Next is the tires rebalanced / trued at a tire shop that uses the Hunter 9700 and see it this works. If that doesn’t improve the ride, the power steering unit is next.

I think it's several little things contributing to the problem. Light cars with imperfect radial tires. The lack of a rag joint in the steering column. Manual steering rack has more feedback than your cadillac's power steering ever would. And probubly fifty other things I can't think of. Every cobra I have driven with this problem did have 60 series tires. And it's only a transient problem 60-65 mph then goes away. Other than that I dunno

No wheel shake at any speed. Have a CMC mustang II rack, 15" american racing mags with 225/60R tires by cooper. Been as high as 115 mph no shake or vibration.

Rich

Yesterday I took all five of my wheels (Trigos) and tires (BFGs, mounted) to my local Chevy dealer(he had the machine I needed) and had the wheels turned on a Hunter 9700 machine. This machine checks the rims for out of round, checks the tires for force variation and checks the tire/wheel comb for balance. All five of the assemblies were in balance. All five wheels were found to be round. Two of the tires had major force variation. One front and one rear were off by 30 pounds. The technician thought it was excessive. I made the bad guy in the front my new spare. The rear guy I will replace.

The wife and I went for a ride during the afternoon and the shake was noticably reduced. When I get the potato replaced on the rear I will report the results.

If you have a shake, have your wheel/tire assemblies checked on one of these machines. The hunter site (www.gsp9700.com) will give you the location.

Bob

Spare what?

Shimmy a Bye Bye
 

This Hunter machine WORKS!

I had a pretty noticeable shimmy between 45 and 60 until today

This website gives you your local dealer with the machine.

Best $17.00 I've spent. Come to think of it, I think it's the cheapest thing I've ever done for my car.

http://www.gsp9700.com/:LOL:

Nothing like a good balance. I can't tell you how many times I have heard of a shimmy or vibration in the 60-65 MPH range that was cured by a good balance. Just because a shop balances them does not mean it will be good enough for our use!
Rick

I have been fighting this phenomenon too. Up to 60mph on smooth asphalt it was ok but past that and it began to shake. Much worse on concrete freway with the tar strips. Tires and wheels had been spin balanced. Yesterday I went to Roger Kraus Racing and had them Dynamic balance the two front wheels & tires on the Hunter machine. It necessitated puting a small (1/2 oz) weight on the polished outer surface, with the rest of the weight to the inside. I am going to put the wheels back on the car tonight and test it tomorrow and will report back. I sincerely hope that was all I needed.

Rick

PS: As a side note to the following post, perhaps the tri bar knockoffs themselves affect the "shimmy" after the wheels have been balanced off the car? Food for thought????

This is a good post for any type of vehicle owner. Just to add one of my own experiences with my everyday vehicle. I have an LR Discovery that came with security nuts on the alloy wheels. I suffered wheel vib and after three attempts to have them balanced (with no cure !) took a closer look. I took off the nuts and weighed the security nut in comparison to four remaining standard nuts - it was 2x as heavy. So replaced the security nut with a standard nut...end of problem.
regards to all on CC
charlieh

Here's what I have, and no shake or shimmy
 

OK, not original at all but dead tight and smooth!

Column is an all rebuilt unit from a 1986 T-Bird. Has 6 way tilt and all-new power assist.

Wheels: Billet Specialties Rebels, 17 inch

Front tires are Pirelli P-Zeros at about 10.5 inch diameter


The handling and rock solid smoothness has to be experienced. It's one of the things that were not screwed up in my "turnkey" :rolleyes:

I don't think there is a problem with the 17" wheels and tires shaking. The problem is with the 15" tires. My Goodyear Eagle 1's are way off, especially the rears. Manufacturers defect. The place I had balance them said I would be better off to buy two new ones as they were off by a pound each.

Ross

I know that the OEM boys. Ford, GM, Nissan, etc. always deal with hormonics in a chassis. I had a collision shop for over 30 years. A Nissan Pathfinder has a 3 lb weight cantilevered off it's right rail about mid way under the "B" center piller post. It's there to counteract the hormonics engerated throughout the chasiss. The shaking/shimmy is a common problem among all brand of Cobra replicas, and I believe is related to hormonics, and may be lessened by doing some of the things spelled out.

I just dug this out of my files and thought if might shed some light on this topic.

The 65 MPH "Shimmy"
This is fairly common although it is usually corrected fairly easily.
First and foremost, be sure your tires are properly balanced. It must be done by a competent technician using a dynamic balancer. Some shops perform dynamic balancing, but they don't do it correctly. It should be done using a more sensitive setting and the technician should properly install the balancing weights. It should also be re-checked after weight installation. In addition, most major tire manufacturers put a marking on each new tire to indicate the "heavy spot" on the tire. Kevin Lakkis, field development engineer from Toyo Tire, notes:
Toyo measure uniformity – Radial Force Variation, Lateral Force Variation, Balance, etc. AND no tire leaves the factory beyond certain limits. (That is why Toyo has so few vibration complaints).
Every Toyo tire is marked at the low balance point with a yellow dot (it is not always a yellow dot with all tire manufacturers, but it is with Toyo). OE tires are also marked with a red dot, marking the low RFV spot (so they can be match-mounted with the rim).
A general rule is to match the yellow dot to the valve stem, however, many wheel manufacturers drill the valve stem hole at the light spot of the wheel.

In any case, when I mount my own tire, I spin up the wheel alone, mark the heavy spot, and match that to the yellow dot on the tire. In my limited experience, the heavy spot of the wheel is not always near the valve stem.

BTW, there is a new balance machine that puts a load roller wheel on the tire and actually measures RFV as well as balance. We are ordering one very soon. That type of machine should help with the 65mph shimmy. I plan to work with my local chapters with people who can’t seem to get rid of the vibration, and note exactly how sensitive the Miata is.
Check out this link: www.GSP9700.com
We (Toyo) have been using one of these machines for some time with excellent results.
We use it to diagnose vibration complaints.
There is a dealer locator which will help Miata owners find a tire dealer who has one of these special balancing machines. Since the GSP9700 is significantly more expensive than standard balance machines, it is safe to assume a tire dealer who owns one is an expert on diagnosing vibration problems.
Finally, if all else fails, take the tires to a specialist and have them "shaved" to 100% true. Manufacturing anomalies are not as uncommon as one would think. Shaving the tires will bring them back into the "round."
Next, the car should be properly aligned by an alignment specialist. Just because the car is new, don't assume that it has been properly aligned at the factory or by the dealer. Many dealers are not very good at alignment. Go to a specialist! If you want to get a very accurate alignment, tell them to let you sit in the driver's seat while they're doing it. The additional weight on one side of the car affects the alignment dramatically.
Consider installing aftermarket bracing to help reduce frame flexing. A rear subframe brace was standard from '92 to '96(?), but can be added to earlier models. A front subframe brace can be added as well as a shock tower brace. The combination of steps should eliminate the shakes.
If that doesn't take care of it, check out Dunlop Tire's description on troubleshooting vibrations.
Here's another tip that was sent in by Brent Tomerlin
I work with a large tire company and over the years I have had plenty of people with "uncurable" balance problems. These were on all cars, not just Miatas. They best solution I have found is to have the tires match mounted. This can be done with a balance machine with a match mount program. What happens is through a process of certain steps the machine figures out the high and low spots of both the wheel and the tire. It then instructs you where to line them both up. This will decrease the weight needed and also give the smoothest ride possible. I've also found that once you air the tire up the final time it's best to deflate once more just in case any air is trapped between the tire and wheel. This is a tedious process as you must semount the tire 3 times for each wheel and usually takes about an hour or so for 4 tires. Maybe two or three times in 6 1/2 years have I had somebody still have a vibration problem.

posted by Doug Reed, Reed Peformance, SPF dealer

Steering wheel shake
 

A couple of Valiums cured mine, temporarily.

Doug,

That is good advice. The place (ATI) that balanced my tires used the GSP9700. The machine does a great job. My car doesn't shake as much as it used to, but the rear tires are so out of round, ATI said I would be better off to buy two new ones. When they removed the tire from the rim, it looked like Goodyear overlapped the belts when manufacturing the tire. This is probably the cause.

Ross

My car has the problem as well. Early Superformance (#117) with Trigo's and Goodyear Eagles with 6000 miles on the car. I assumed it was a tire balance issue however now I know I am not alone.

Doug

Re: Here's what I have, and no shake or shimmy
 

Quit ragging on how piss poor your car was delivered. I speak for myself but I/m sick of hearing about it.
Dig at the builder every time you post--real frigging class%/

So you got a "lemon" learn to fix it into lemonade don't harp so--you are sounding like a whiny spoiled child that didn't get his way. WHAA! WHAA! WHAA!-- for darn near a year. Always the builders fault, never yours.

Sure you spent money on your car--we all did some of us have had problems "lemons" but eventually we made "lemonade ".

Seems like there are several WCC owners out there that have nothing but good to say about Vern Redel and his builds.

Sort of puts you in a questionable light, especially since we've only heard you side of it:LOL:

Ya'll have a good one, today:rolleyes:

GR
 

You are one of the grouchiest and nastiest people on this site and I am sure I speak for many here that they would not miss you if you stopped posting. Do take some viagra and try to have a great day.. I will.. :cool:

:LOL: