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  #1 (permalink)  
Old 11-02-2008, 03:10 PM
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Default Body Vibration

Has anybody experienced a vibration that happens at relatively high speed? When I get above 60 in 4th or 5th the body vibrates but it has a rhythm. As I get over 80MPH the vibration stops. I just got new tires and alignment and thought I had fixed the problem. It's a side to side vibration because I can watch the steering wheel vibrate with the car. Could it be front end tie rods? All the bushing are original (1996). Like I said right after the alignment and new tires it was smooth.

Any Help Always Appreciated.
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Old 11-02-2008, 07:15 PM
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Scott,
You are describing perfectly what I have explained many times! It's been called "cowl shake: since the first Cobra hit the street, At higher speeds it will rythmically vibrate the car. I have seen guys put new wheeels on, new tires, new tie rods, U-joints, driveshafts and even change the rear end gears- usually all for naught.

The force of the wind going through the nose and around the motor is hitting the firewall causing it to shake and create exactly what you are talking about. Usually starts above 45 mph, gets milld then really starts to shake things up[ over 60 to 80 mph, the funny part is drive over 80 and it ususally goes away.
The key with a CR car is to make sure the body is sealed tightly on the firwall from side to side, usually with caulking. (This is NEVER mentioned in the asssembly maual.

Check you car where the body sits down on the firewall, chances are it has never been glued. A full caulking gun works great but usually on a built car there just isnt room, in that case three or rour tubes of permatex and lying on your back will do a fine job.

DV+
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Old 11-02-2008, 08:19 PM
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DV,
I believe you talked about something similar recently, referring to fitting the body down on top of the firewall. Trimming the top of the firewall and placing a rubber gasket along that edge. Is this the same thing? I know my body is not glued down (or have a rubber gasket for that matter) at the top of the firewall and it seems this would really tight up the body if it was. If I'm on the right track here do you glue it by accessing it from under the dash? And are you suggesting using Permatex RTV silicone? Thanks!

John
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Old 11-03-2008, 03:28 AM
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Masnaka,
Eactly, if you are putting the body on for the last time then I used wto long section of the old windshield install kits. I run two strips on op of the firewall annd let the body sit down on that. But, since the body is already down then about the only thing you can do is get up inside and outside and permatex it as elll a you can.
DV
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Old 11-03-2008, 04:54 AM
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I don't know if this has anything to do with "body vibrations" at speed due to air being forced around gaps in fit in the firewall or around the body, but here is what I did.

I used "spray insulating foam" from Home depot (about $5.00 a can) to seal up between the body and the area near the exhaust headers and the sidepipes. I had a lot of heat coming through into the foot box, this fix it perfectly. A little of this stuff will seal up just about anthing else you need to seal, especially if it's in a difficult place to get at.

Anyway it's worth a shot, Bill
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Old 11-03-2008, 05:18 AM
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Thanks guys, Home Depot here I come!
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Old 11-03-2008, 04:37 PM
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Hey BE CAREFUL with that insulating foam in a can. That stuff can make a real mess and I don't believe it will come off the paint too willingly. There are also two types at home depot. One is low expanding foam and dries soft, the other is expanding foam and dries stiff. That expanding foam will cure into some very intereting shapes as it hardens. I would stay away from the expanding foam. Just be aware a little goes along way and there is no easy way to clean it up. I guess paint thinner and a rag might work.
Read the label on the can.
John
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Old 11-03-2008, 06:11 PM
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John,
I couldn't have ssid it better-my thoughts for the body to COWL stick with some type of siliacone.
DV
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Old 11-07-2008, 07:26 AM
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Will do, I never liked the expanding stuff anyway. It's almost impossible to get off your hands!

I don't have the body painted so I am not worried about that. I just don't want to go throught the pain of pulling the body.

Hopefully this will cure the problem. I will post my success or lack there of by the end of the weekend

Thanks Again,
ScottS
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Old 11-09-2008, 03:29 PM
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Well, the silicone and non-expanding insulation went on yesterday without a hitch. Of course my back could use a good massage

I waited 24 hours so that it could seal good. but alas, to no avail

The vibration is just as pronounced as before.

The only thing I can relate to is a baja bug that I put together way back when they (and I) were popular. It was a convertable and I took off the convertable top and it started to have the same side to side vibration/occilation. So, I got my welder out and my pipe bender and fabricated a roll bar that would bolt on like the convertable top. Sure enough it solved the vibration problem. So, I am thinking that maybe there is a need for some stabalizers in the engine compartment.

So, I am looking for any and all suggestion. Before I am through I may just have a MadMax road warrior!

Scott
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Old 11-09-2008, 05:13 PM
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Scott,
Do you have the door piller braces in that run from the frame in the rear tire area? If you don't, that might help. Also check all of your body attachment bolts to be sure that all is tight. Do you have large enough washers on the body bolts. If not there might be fractures and allowing the body to move.
Just things to think about, Terry
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Old 11-09-2008, 06:34 PM
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Scott did you get my pm regarding tires and balance?

John
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Old 11-10-2008, 03:48 AM
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I will check all the body mounts and go through once again to make sure I have enough attachments up front. I believe I may be a little shy on the front mounts.

I am not sure I know what a "door pilar brace" is but I will consult the manual to find out.

Plus, I don't think I got John's PM. In fact I don't even know what a PM is (I just hope he didn't mean BM)....

Thanks Again,
Scott
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Old 11-10-2008, 04:09 AM
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Scott,
What you;'re describing still sounds like the body is moving somewhere?(Although you can't rule out a tire imbalance, but if you didn't have it before, why now?) I do have to admit this is the first tiime I've heard of this and sealing the body to the cowl didn't fix it!
We will stay tuned- give us a new answer!
DV
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Old 11-10-2008, 05:56 AM
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Scott,
The door piller brace is the one in the rear fenderwell that goes from the frame to the door latch. It is in the front of the fenderwell. If you can't find it let us know and I will attach a picture of it.

Terry
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Old 11-10-2008, 09:13 AM
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Scott,
PM = Private Message located in the upper right hand corner of the home page. Click on it to receive.

I was having some serious lateral shaking issues until I replaced the bias ply tires with radials. Now no more shaking. The shaking I was experiencing was occuring at 35-40 and again at about 70mph. You mentioned that you recently put on new tires and I thought this might be the reason. What kind of tires did you install? You might want to have the balance checked and roundness checked. Some tire manufacturers are notorious for out-of-round tires. If you weren't having the shaking before the tire change then this is where I would be looking. If you were then it seems the body shake is a result of something else.

John
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Old 11-10-2008, 09:53 AM
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Also lots of high performance tires are directional and they could have them mounted wrong----

And bias/radial mix doesn't work either
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Old 11-11-2008, 04:08 PM
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Scott,

A couple other things came to mind which may or may not help...but could it be your driveshaft causing the vibration? and or possibly a bad shock. John
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Old 11-16-2008, 12:37 PM
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Just got back in town.

I do have the door pillar braces installed. I am going through the front end body attachments this afternoon and hopefully get a run in before dark.

Thanks Everyone,
Scott
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Old 11-16-2008, 03:26 PM
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What did the wear patterns on your old tires look like?

Vibrations coming up the steering column tells me it's front end...
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