I have a 1985 Corvette which I have owned for three years. I have new tires and have had the rims repaired/refinished. I still have a little vibration that comes on at around 80 MPH, feels like the rear (not in the steering wheel). This vibration does not appear to get worse at higher speed though I gaven't had it much past 100 MHP and then only fo a very short time. I am going to replace all the bushings this summer and would like to take care of this problem while I had the rear assembly apart. Anyone have a simillar problem and found the solution? I am thinking a 1/2 shaft u-joint of maybe a drive shaft u-joint. Also can you replace the driveshaft u-joints without removing anything other than the driveshaft?

 

Hey Bill, you may be looking in the right place. I suggest using this Forum's search function. There's a plethora of info on U-joints,halfshafts, etc.

 

Thanks, I did a search but didn't see any complaints of a vibration comming on at such a high speed. Thought maybe someone had a similar problem. Ill have it up in the air and check all the u-joints as best I can. When I was searching I found some photos of u-joints replaced by a member and they lookes to be nothing but rust, hard to believe they didn't fail.

 

I went round and round with My '85 over a similar vibration (become noticeable about 80 mph, not get much worse with higher speeds but not go away either..). Had the shafts (all three) balanced, new U-joints, New wheel beraings (all around), different wheels and tires - nothing fixed it. I ended up living with the vibration for a couple of years.

Then, started playing with burning my own PROM chips. I discovered that I could make the vibration go away if I pulled timing advance out of the motor at 2000-2400 rpm. I still don't really know why, unless it was some sort of an exhaust resonance/vibration that was transferring to the car, but taking a chunk (like 10°) of timing out of it at those rpm's (and loads for interstate conditions) cured it. It was NOT any sort of mechanical driveline or suspension problem - just more ignition timing than the motor liked at those RPM's and loads.

BTW - taking all that advance out of it did not affect the fuel mileage at all. It did make a very slight noticeable difference, call it a flat spot - a very small one, when accelerating from, say, 75 mph on the highway - but hardly even enough to feel.

Since then I've swapped motors (from mostly stock to a Vortec 330 hp GM crate) and started over with the chip - but the same sort of vibration issue Can be (I've avoided it, but the possibility is definately there) repeated with this combination I have now. I still believe that it's an exhaust resonance issue - perhaps a true dual system or something much more tightly attached to the car would also "cure" it.

 

Since it's not a serious issue I would start by rechecking wheel/tire balance first (you could have thrown a weight). You didn't say how many miles are on the car. If you are going to replace the bushings anyway that's fine but it may not be the problem. Then go on to check u-joints etc. I would have a shop put it on a lift to check that.

 

I recommend new U-joints if you don't know how old the ones on your car are. I just pulled a halfshaft last night.....omg! The u-joints are terrible. With the shaft out of the car, I could barely budge the u-joints with my hand. All the grease was gone and some were rusty. My car started squeaking about a month ago, and a couple days ago started clicking and grinding. It was the u-joints in the driver's side halfshaft. Not only was my car making some noise from the back, but I was likely losing a significant amount of hp and mpg.
U-joints probably need to be done anyway, so you might as well start there.

 

New U-Joints and a alignment

 

For me new wheel bearings solved the problem. Before the vibration would start at around 85 and not get much worse.

 

Thanks to everyone for the response. The car has 80,000 miles and they have never been changed (the first owner told me everything that had been done). I will plan on changing the 1/2 shaft u-joint while I have it torn down.

 

I believe the is a drivetrain dampner at the tail of the transmission similar to a harmonic balance only smaller. You might look it over as well while your doing u-joints.

 

If you had your tires/wheels balanced on anything but the Hunter GSP 9700 vibration analyzer, you didn't get them balanced.

http://forums.corvetteforum.com/show...ght=Hunter+GSP

Tom Piper

 

 

It's amazing how poorly balanced/out of round some tires are. I've had to send back 3 (out of a set of 4) Kumho 712 Ecstas and 2 of 4 Nitto 555R's (cheap brands equal more work).

Using a Hunter 9700 showed that the tires themselves were quite out of balance while proving the rims to be non-suspect. The tire manufacturers were unquestioning when presented with the data (they both asked if I had "road force" balanced the tires). They were quick to send out replacements.

On the other hand, some "tire techs" are pretty dull about balancing tires.
Many don't know why there is a "dot" on the tire and what to do with it... (heavy part of the tire...line it up with the valve stem). I've found that sometimes they add way too much weight which will make the tire seem smooth up to about 75mph but will add a very "heavy", low frequency, high amplitude vibration at speeds above.

If it is not absolutely smooth above 100mph then I take it back until the problem is solved.

 

You can always go to a good dealership that has an EVA-2 and pin point the vibration.