vibration at 35-55mph...mechanic doesn't know what it is

[miliue]

I just took the car in to my indy for a new clutch, flex disc, center bearing, and tranny mounts.

Now, the car runs smooth as silk except:

In the morning there is an audible whine that starts at about 20mph and persists until around 35mph. It sounds like when you rub your finger around the lip of a wine glass. That wooooo sound. It doesn't matter what gear I'm in, as long as I'm at those speeds, the wine persists. In the afternoon, the sound goes away.

At approx. 40 mph the car vibrates. I feel it through the seat, not the steering wheel. There is no audible sound, it just vibrates. It's not a violent vibration. Again, it doesn't matter what gear I'm in, as long as I'm going between 35-55mph, the car vibrates.

After driving the car for 30min or so, the vibration lessens. For instance, my indy took the car for a test drive and he felt it. We lifted the car, looked all around, couldn't find anything, and took it out again. Now the vibration was gone. This happened yesterday. Today I took it back and the exact same thing happened. Neither one of us has any idea what the problem could be. Indy said it could be something with the driveshaft but he couldn't diagnose it.

He said to just drive it and if it got worse to bring it back in. He did offer to cover any expenses if it turned out to be a result of his workmanship or the parts he installed.

Anyone have any idea what this could be? I'm stumped and the sound + vibration is driving me crazy.

[tnt525i]

my guess would be the center bearing, probably its not aligned properly,, on the bearing housing where you bolt it to the body of the car, maybe its too far back on the driveshaft or too far foward,, maybe someone with a bit more experience could help you more.

[Robin-535im]

Taking some shots in the dark here, but if it were my car I would rotate the tires front to back to see if the vibration went from your butt to your hands. If so, I would suspect the tires are flat spotting, out of balance, etc.

If that does nothing, I would suspect a bushing in the rear of the car, or perhaps the driveshaft / center bearing. I don't know how to check the driveshaft really, without pulling it and balancing it out.

Some of the rear bushings you can inspect visually (pull off the cover plate to look at the beercan bushings, visually inspect the pitman arm / "dogbone" links, put your hand on top of the rear shock tower (have to pull the rear seat) and have someone jump/shake the car to see if there is movement in the upper shock mounts. The problem is, maybe a bushing is bad but it looks fine, or vice versa, and you're back where you started...

Drive it a lot over bumps and different road surfaces, try to see what the vibration is a function of. Speed? Force on the suspension?

- Robin

[jjw]

Have the tech. pre-load the center bearing? Sounds like drive shaft vibration.

[blackpawn5]

I would say an alignment issue with the vibrations, but the sound... does it get louder when you slow down is the noise more apparent? if so i would check the power steering, on my 535i i spent weeks trying to figure out what a sound like you described was coming from and it was my power steering it was a little low but not much that the stteering was affected.

[miliue]

Thanks for all the advice. I plan on checking the tires tonight to make sure they're inflated to the right psi and all that. Tomorrow I'll rotate them and see if anything changes.

As for the sound, I do know that I'm leaking power steering fluid very very slowly. More like weeping than leaking. But I wonder if I might be low like you said. I'll definitely check it out tonight.