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10-08-2002, 05:07 PM
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CC Member
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Join Date: Nov 2000
Location: Houston,
Tx
Cobra Make, Engine: Unique FIA
Posts: 2,064
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Not Ranked
Are we talking "cowl shimmy" or actual steering wheel shake?
__________________
All my ex's live in Texas
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10-08-2002, 05:16 PM
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CC Member
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Join Date: Jun 1999
Location: Woodinville,
WA
Cobra Make, Engine: VICTORY, 92 C.I., belt drive, saddle bags.
Posts: 666
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Not Ranked
Shimmy, Rattle, and Roll
For me, its plain ole front wheel shimmy. I have little to no cowl shake due to the design and strength of the Can Am chassis.
But.... the notion that my rack (steering box) and dampener needs catering to is what I am hanging my hat on this moment.
I would like to know more of the truth about the phenomena of "induced" or "inherent" shimmy due to the design characteristics of the "cobra" suspension set up. Could that be the actual root cause which then requires suitable remedy to correct?
Hmmm.
Zderf
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10-08-2002, 05:28 PM
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CC Member
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Join Date: Sep 1999
Location: New Orleans, LA , USA,
Posts: 195
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Not Ranked
Hormonics? Anyone who has worked as a collision technition will tell you that most cars have hormonic off-set weights possitioned on the chassis somewhere. I am certain that most Nissan Pathfinders have a 4 or so lb. weight bolted hanging off the frame just under the pasenger side "B" center pillar post. This is to counter-act the hormonics generated by the engine chassis/suspension. I believe we are all dealing with some hormonics in all makes of our cars. Shaving and truing tires and all the other remedies mentioned and you may still have a slight shaking due to the hormonics. Live with it and enjoy your ride, a small price to pay for our enjoyment of a real performance car.
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10-08-2002, 05:36 PM
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Senior Club Cobra Member
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Join Date: Mar 2001
Location: Southern Connecticut,
CT
Cobra Make, Engine: SPF - 351W, 944 non-turbo
Posts: 2,105
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Not Ranked
Hey Jim:
Believe me I read your link. I've put a lot of thought and effort into trying to eliminate this problem. While I understand that it may go away for some owners when they balance the tires or get the wheels aligned, for some of us it just goes on.
I would love to put my tires on one of these Hunter machines your link recommended but I have not been able to find one. I am convinced that 90% the vibration comes from the tires with maybe 10% coming from the wheels. I understand that tires that are dimensionally round may not be round dynamically. When they roll under load they go up and down. When I worked for Armstrong Rubber (as a tire engineer for 12 years) we had a machine that could identify these out of (dynamically) round tires and correct them. It was only used for OE tires!
There is a good chance that little cars with big (heavy) tires are more prone to this condition than are heavy cars with little tires. One the harmonic sets up (60 to 80MPH) there is really no way to stop it. I think the shake comes and goes because the tires do not roll at the same rate and cancel and reinforce the vibration as the car progresses down the road.
I have been driving now for 40 years. When I started driving in 1962 there were no such thing as dynamic balancing or computerize alignment. In spite of lacking the new high tech gizmos cars of 40 years ago did not have steering wheel shake! I driven a number of rust buckets over the years and none of them had steering wheel shake!
Could it be that radial tires and Cobras do not get along well? Could it be that Trigo wheels are not round?
Bob
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10-08-2002, 05:54 PM
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CC Member
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Join Date: Aug 2002
Location: Dacula, (Atlanta),
GA
Cobra Make, Engine: Unique 427 SC, Southern Automotive 427W Stroker
Posts: 1,649
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Not Ranked
I didn't set up my Unique, but I can happily report that the steering (and car for that matter) are rock steady at all speeds. I'm running the standard setup i.e. MGB steering assembly and Compomotive 16" wheels and Goodyear rubber.
__________________
After a good hard ride.....oil pressure is over 50, temp is below 190, she idles and no new dents. LIFE IS GOOD!
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10-09-2002, 04:45 AM
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CC Member
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Join Date: Nov 2000
Location: Houston,
Tx
Cobra Make, Engine: Unique FIA
Posts: 2,064
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Not Ranked
My Unique also has not had steering wheel shimmy, but it did have a cowl shake at around 60 mph. I got the wheels balanced
and it went away.
My friend's Classic roadsters has a harmonic type of body shudder at 60 to about65 mph. ( feels like it starts at the rear then
passes through the middle of the car and goes out the front, does this over and over) An inspection revealed that the rt rear tire
is out of round radially by about 1/8 " We suspect that is the cause. Does anyone know where to get a tire shaved in the Houston
area?
Steven
PS do they use shaving cream when doing so?
__________________
All my ex's live in Texas
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10-09-2002, 05:55 AM
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CC Member
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Join Date: Feb 2000
Location: St. Lucia, West Indies,
WI
Cobra Make, Engine: Unique 427SC 383 stroker
Posts: 3,767
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Not Ranked
My Unique used to have a very noticeable shimmy at around 50 - 60 mph - I have to guess because the speedo didn't work back then. During the rebuild I swapped out the old MGB front suspension for Unique's newer coilover setup with the adjustable shocks, new rack, etc. At that time, I also installed 15 X 7.5 & 9.5 PS Eng. bolt ons with BFG 245 and 275's. Now there is no shimmy at any speed and I'm very pleasantly surprised at the quality of ride and handling. There is a bit of twitchiness at high speeds, though, due to a slight toe out up front which I will correct as soon as my tire shop finishes setting up their new alignment machine.
__________________
Tropical Buzz
Grant me the serenity to accept the things I cannot change, the strength to change the things I can, and the wisdom to know the difference. -(wasn't me)
BEWARE OF THE DOGma!! Dogmatism bites...
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10-09-2002, 08:14 AM
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CC Member
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Join Date: Apr 2000
Location: Leesburg,,
VA
Cobra Make, Engine: ERA Cobra #273, 427 S/O, ERA GT-40 #2057, Excalibur Cobra.
Posts: 1,011
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Not Ranked
BOB IN CT:
THE LINK TO HUNTER'S SITE IN JIM C'S POST TAKES YOU TO HUNTER'S "SITE". AT THE TOP RIGHT CORNER OF THE PAGE CLICK ON "LOCATE A GSP9700".
I LIVE IN ASHBURN, VA (2.3 MILES FROM NOWHERE) AND THE SITE IMMEDIATELY PRODUCED 41 SHOPS WITHIN 25 MILES USING THE GSP9700. THE PAGE LETS YOU SEARCH A RADIUS OF 10, 25 OR 50 MILES. FIVE OF THE SHOPS ARE WITHIN SIX MILES.
GOOD HUNTING AND - - - - Y'ALL HAVE A REALLY GREAT DAY,
BLACKJACK
__________________
It's impossible to make anything FOOLPROOF - - Because FOOLS are so ingenious.
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10-09-2002, 10:01 AM
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CC Member
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Join Date: Oct 2000
Location: Lake Stevens,
WA
Cobra Make, Engine:
Posts: 995
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Not Ranked
My older Unique was rock solid when I first got it with the 16" wheels and Z-rated Potenzas. When I replaced those with used 15" Compomotives and new BFG's it started shaking wildly at various speeds. After 3 trips to the wheel balancer only the front shakes slightly between 60 & 70. I met a guy with his own brand new mounting & balancing set-up and as soon as I get time I'll run them through the mill again.
Rich
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10-09-2002, 10:55 AM
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Renegade Nuns on Wheels
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Join Date: Aug 2001
Location: columbus,
Oh
Cobra Make, Engine: Unique 427 roadster with 351C-4B
Posts: 5,129
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Not Ranked
Rich, question please
What year is your car? Or chassis number. What size tires have you run and have any of them rubbed.
Thanks
Rick
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10-09-2002, 11:06 AM
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CC Member
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Join Date: Oct 2000
Location: Lake Stevens,
WA
Cobra Make, Engine:
Posts: 995
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Not Ranked
Rick,
It's a 1990, chassis #9063. The tires are 235/60's & 295/50's. And yes, if I hit a large dip in the road they rub. I think that's due more to the worn out rear springs than the tire size.
Rich
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10-09-2002, 11:12 AM
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Renegade Nuns on Wheels
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Join Date: Aug 2001
Location: columbus,
Oh
Cobra Make, Engine: Unique 427 roadster with 351C-4B
Posts: 5,129
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Not Ranked
Thanks Rich
So they only rub on the rear? I am planning on going with the new Kumhos that are 255 and 275/60 and trying to get a feel for if someone has run that size. Currently I have 225/60 and 275/50 and they never rub.
Chassis 9063! I have chassis 9007. We should compare notes. Are you still running the MG front end? Jag brakes? What have you done to your chassis and brakes? I am anxious to compare notes with someone else.
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10-09-2002, 01:18 PM
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CC Member
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Join Date: Oct 2000
Location: Lake Stevens,
WA
Cobra Make, Engine:
Posts: 995
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Not Ranked
Rick,
If I had it to do over again I'd go with the 255 & 275's.
As far as chassis & brakes, I haven't done a whole lot. The car still has the MGB front suspension, and other than some tired bushings, it handles great. The few things I have done, such as a 50% larger front sway bar and new steering couplers, have made a huge difference. Polyurethane bushings and new front Konis are on the schedule for this winter.
I want to see some pictures of your front suspension set up.
Rich
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10-09-2002, 06:20 PM
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CC Member
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Join Date: Aug 2002
Location: Dacula, (Atlanta),
GA
Cobra Make, Engine: Unique 427 SC, Southern Automotive 427W Stroker
Posts: 1,649
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Not Ranked
Rich,
Out or curiousity, why did you change your wheels? Sounds like you were better off before (ridewise). Did they look bad?
Tony
__________________
After a good hard ride.....oil pressure is over 50, temp is below 190, she idles and no new dents. LIFE IS GOOD!
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10-09-2002, 06:57 PM
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CC Member
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Join Date: Oct 2000
Location: Lake Stevens,
WA
Cobra Make, Engine:
Posts: 995
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Not Ranked
Tony,
I was better off ride-wise and the handling was much more crisp (crisper?). The old wheels were a black mesh, BBS style right out of the 80's. I wanted a more classic look and, at the same time, something different than all the other Cobras.
These have just the look I was after:
http://www.clubcobra.com/cgi-bin/pho...=2105&size=big
Rich
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10-09-2002, 07:06 PM
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CC Member
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Join Date: Aug 2002
Location: Dacula, (Atlanta),
GA
Cobra Make, Engine: Unique 427 SC, Southern Automotive 427W Stroker
Posts: 1,649
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Not Ranked
Rich,
Nice car, real nice wheels. If that's your house in the background, you must be related to Bill Gates!
__________________
After a good hard ride.....oil pressure is over 50, temp is below 190, she idles and no new dents. LIFE IS GOOD!
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10-09-2002, 07:12 PM
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CC Member
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Join Date: Oct 2000
Location: Lake Stevens,
WA
Cobra Make, Engine:
Posts: 995
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Not Ranked
Tony,
Thanks!
That's the summer place. Any resemblance to the Sun Valley Lodge in Sun Valley, Idaho is purely coincidental.
Rich
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10-09-2002, 10:01 PM
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CC Member
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Join Date: Apr 1999
Location: Illinois,
Posts: 123
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Not Ranked
Unique chassis #9047
Hi guys - Good to see your posts! I'd be interested in comparing notes also. I running 245/60 and 295/50 BFG's on Americans. I have a slight steering shake around 60 that I have been trying to remedy. I think I'll try finding a shop to balance the tire assembly on the car. That seemed to worked for a couple of the other guys on this forum. I would be happy to hear what has worked on your cars also. Len
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10-10-2002, 04:27 AM
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CC Member
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Join Date: Nov 2000
Location: Houston,
Tx
Cobra Make, Engine: Unique FIA
Posts: 2,064
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Not Ranked
To you front end gurus:
Do you think adding a little more caster would help eliminate some of the shake reported here?
__________________
All my ex's live in Texas
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10-10-2002, 08:47 AM
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CC Member
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Join Date: Jun 1999
Location: Woodinville,
WA
Cobra Make, Engine: VICTORY, 92 C.I., belt drive, saddle bags.
Posts: 666
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Not Ranked
How Unique
Well this certainly has turned out to be a Unique thread!!
Rich... of course you post the coolest picture of your car ever, in front of my place... show off.
I sure hope some "shimmy remedy" comes from all of this. I Hope I hope I hope......
Zderf
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