In om>, " > writes:
>> My 94 convertable starts to vibrate around 65 mph.
>>
>> Feels like it is in the back of the car. Can feel it through the gear
>> shift, so could it be drive shaft? Car is just at 100K.
>>
>> Recently acquired the car, first vette, so no history on the car and not
>> sure where to start looking.
>>
>> Is this a common problem, or do I just go through the check the tire
>> balance, rim straightness, etc. routine?
>>
>> Everything feels tight. No clunking on acceleration or deceleration, so at
>> this point I don't suspect U-joints.
>
> I'd like to hear from someone with a late model C4 that has
>absolutely no vibration at 65-75mph like my 2003 C5. I've fought with
>vibration in that speed range since my 1996 C4 was new, it's about
>115K now. It seems like there's a body resonance that is always there
>but strongly magnifies any problem. Mine seems to be towards the
>front. Wheel balancing and tire changing make a difference but don't
>eliminate the problem. The last round after the vibration got worse
>replaced a worn ball joint which helped a lot. I drive the C4 to work
>twice a week and the 65-75mph vibration is worse in the first few
>miles and calms down as the tires warm up. It's almost as if the
>tires take a set when they sit like old nylon belted tires did. This
>is the same for Goodyear GSC's and Firestone Firehawks.
> That being said, there are a lot of things about my C4 that I like
>better than the C5. By all means, have the items mentioned elsewhere
>in this thread checked in case there is something that needs attention
>but don't worry about a little residual vibration. Nothing I've ever
>driven is as comfortable cooking into a turn as a C4. Enjoy your new
>vette.
>
>

Same experience with my '89. I think you've got it right.
First 8 miles on the freeway on winter mornings are the
toughest (I hold it at 62 mph while warming up.) Definitely
worse with tires that have 'noise reduction' belts.
(Yokohama dB2s front and ES/100's on the rear). Adding
the convertible frame brace to my coupe helped.

The 'soft ride' suspension seems more sensitive to older tires
with hardened tread.

Probably gets worse when 'Dad' rides in a C4 --
definitely a shakey character -- when he's around
L98 or LT1 engines, he rattles around a lot and gets
very noisy. {{--0(

Yeah, the C4 is more fun than the C5 for freeway
on-ramps and off-ramps.

--
pj