C4 Vibration

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.
Ideas anyone?
Thanks!
Alex
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Alex wrote:

Welcome and enjoy!
Sixty-five is a typical speed for a C4 tire balance problem to raise its ugly face.
You 'to-do' list looks good. Add the following:
Assuming you have the orginal factory wheels, check to see if some well-meaning grease monkey rotated wheels front to rear.
The original tire sizes were 255/45 on the front and 285/40 on the rear. -- pj
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if you have option z07, the tires are the same size front to back.
regards, charlie
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I thought they started to vibrate when you put them in gear? May be why they were called "Shakers" in days gone by. ;-)
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Sounds like tire balance, but, 100k is about right for u-joints to go out. It happened to my '91 and the symptoms were vibration at high speed, squeaking at low speed, and a weird wandering feel from the back end. There was no clunking.
Like PJ said, clean the inside of the rims first.
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Alex wrote:

Low aspect ratio tires are very prone to a sensitive balance. Clean the rims inside, and have a tire place check the runout of the tire/wheel combo. U-joint "could" be the problem, but generally you will also have the clunking, & noise symptoms also. But 100K is around the time frame generally for u-joints to start showing wear symptoms.
--
Ric Seyler
Online Racing: RicSeyler
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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.
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Snipped some good information

Vibration and body shake was the number one reason I got rid of my '92 with just under 100K on it. The only thing I missed going to the C5 was the engine access of the C4's hood. Those things I like better in the C5 were better ride, no body shake, no vibrations, runflats do cup and get noisy in about 10K, slightly better gas mileage, easy in and out, better view or the road, first car I felt at home in on an autocross course, better insurance rates, less, (much less), rattles, no air leaks under 100 mph, no water leaks ever, plenty of luggage space, and last but not the least feature was to be able to take off the top and drive over 50 mph without it shaking as badly as did the C4.
In fairness to the C4 I've never driven a C5 more than 50K so I have little knowledge as to how the drive train matures. There has been some discussion about losing tie rod ends and that would be my first "look at" to see how firm and maintained they were, then to the back to do the same, followed by the universals. Although my C4 shook like a dog passing razor blades it never required and replacement of these items, just it's nature to shake.
--
Dad
05 C6 Silver/Red 6spd Z51
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writes:

I think the rod-end issue isn't peculiar to the C5 but to other recent GM front ends as well. Both of my wife's LeSabres (01 and 03) have had rod ends replaced -- one at less than 25K miles and two others after 30K. My Sierra had a rod end replaced before 25K miles. The C5 ('02) needed one two months ago @ 23K miles.
Since the cost is nominal I'm not overly excited about the failure rate.
The C4, even with all the cold weather vibration, has not had a rod-end replaced in over 60K miles.
Maybe routine lubrication was a good idea!
-- pj
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I had the same problem with a 75 vette at one time. I found a place that still balances the tires while they remain on the car. that balances the rotor and all. they solved my problem...
g'luck
--
'Key
=====



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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
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My LT-4 has 145K miles on it and it is silky smooth down the road at all legal speeds, a few body rattles going slow on rough roads but not bad at all. Who can say why some cars do better with mileage than others.
I had an RX-7 that the drivetrain would shake when cold but would smooth out when warmed up, felt it through the gearshift too. I checked the driveshaft U-joints and they were tight and smooth but changed the shaft anyway and the problem went away immediately. I'm thinking it might be the driveshaft! Also had a car that would shake only at a certain speed in top gear and no other gears, turned out to be the harmonic balancer on the crankshaft funny though at that rpm in other gears it wouldn't shake, harmonics through a vehicle can be very complex.
And oh I don't think I would trade my C4 for a C5 even with low mileage I have a neighbor with a '98 and have smoked him several times so much so he won't even try me anymore.
Butcher '96 LT-4 CE (with aftermarket exhaust and intake)
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