shaking when Topless

[32valvesftw]

This is a puzzler for me. We just got back from taking the Vette for a drive in the country. Along the way we stopped to remove the Targa top. It was then stored in its place. When I went to pull back not he road, the car was shaking badly, noticeable through the wheel. The shaking was pretty bad so much so that I did go over 50, cause I thought I had a wheel falling off. I did stop and check every lug nut was tight. I did visual of the drive shafts as best I could. I had the wife put the car in gear with he hood up, the engine did not jump, so no broken motor mounts. Then we proceeded on our trip and shaking resumed, I drove slowly for about 10 more miles. Then I stopped to put the roof panel back on, so I could hear better in the car. With the roof in place and bolted in, no more shake???WTH I am puzzled, How could the roof panel have that much to do with it?

[secondchance]

Has the car been sitting for awhile? Temperature today? You may have flat spots on your tires. Taking the roof off may be just amplifying the vibration from flat spots.

[32valvesftw]

I had been driving for quite a while so the flat spots were definitely not an issue. I get those and know what they are. I did some research and it appears C4s do loose some rigidity with the top off. I never had an issue in the past but perhaps the newly added HP and perhaps a tire issue made it more noticeable??? I have not checked up on tire balance but I just had them balanced less than 2000 miles ago.

[gbrtng]

Corey broke it for you - or maybe it was W. .... - oh, never mind ...

TGF

[Gunny]

no answer for why it's suddenly worse than before but my 90 has always been "looser" with the top out. Several years ago I bought a cross bar that allowed a video camera to be mounted, 5 point seat belts, and maybe something else. The big surprise was how it stiffened the body up so much that I no longer had the "looseness" and shake when I took the top off. That "feature" has been much more valuable than the camera & seat belt mounts. Couldn't find a photo of my install but did locate one when I googled it. The cross bar uses the existing holes/bolts from the seat belts and the clips that hold the top inside (the photo I found didn't retain the top clips but you don't have to lose that functionality). This is not a roll bar but I expect a properly installed roll bar would have the same effect. I'm not sure whether this cross bar is still available. Maybe someone else will chime in.

[Gunny]

found another photo

[Kevin]

sounds about right. I can't drive the car with the top off. feels like its going to fall apart. I can tell a difference in the glass vs painted top

[Vette73]

This may help,maybe...Try the rear glass vent hook....It raise the rear glass at lest two inches which makes the incoming air escape faster....I used mine all through the spring and summer months....Also on the highwzy you will notice less wind noise because the air has an escape route...It costs around thirty bucks and I like it..

Forget where I got it from....I know I did not order it from Eklers or Mid-America because I heard some complaints about there design ...

Google it you should find it...Like I sId it's just a suggestion..
They install very easily...

[G8nightman]

In my None z C4 with the top off over 130 mph the rear would lift off the ground.

[Hib Halverson]

Originally Posted by 32valvesftw

This is a puzzler for me. We just got back from taking the Vette for a drive in the country. Along the way we stopped to remove the Targa top. It was then stored in its place. When I went to pull back not he road, the car was shaking badly, noticeable through the wheel. The shaking was pretty bad so much so that I did go over 50, cause I thought I had a wheel falling off. I did stop and check every lug nut was tight. I did visual of the drive shafts as best I could. I had the wife put the car in gear with he hood up, the engine did not jump, so no broken motor mounts. Then we proceeded on our trip and shaking resumed, I drove slowly for about 10 more miles. Then I stopped to put the roof panel back on, so I could hear better in the car. With the roof in place and bolted in, no more shake???WTH I am puzzled, How could the roof panel have that much to do with it?

Significant steering column and windshield shake is typical of any C4 with the roof of. Unfortunately the C4 has pretty weak structure and when you have the roof of it's even worse.