High speed >85 Wobble / Shake

[Royale240]

Hey Nico, I request your help once again!

I've been doing some research on some possible explanations on what's causing my current issue, but I'm not sure what exactly needs to be replaced or adjusted....Here's what's going on.

-I'm cruising along at around 70 and I downshift into 4th to accelerate up to around 90-100.
-everything is fine, everything is stable until I hit 85 mph when things start shaking.
-I hit around 90 mph and there's a very loud audible vibration that begins shaking the entire car.
-whole car is vibrating like crazy
-Steering wheel and shifter are staying perfectly still.
-Slowing down to 65 mph, I can let go of the wheel and not change lanes. no wheel wobble.
-Doesn't follow the symptoms of 'death wobble' or 'death sway'
-Car doesn't want to kick out or change directions at speed on on throttle, just vibrates like crazy.
-I don't feel any sort of vibration in the shifter or the wheel at any speed, or even when I hit 85.

I'm Assuming this means I have some sort of bearings / mounts or bushings that have worn out or have been destroyed. Everything handles great, and suspension feels good (Stock struts and springs, don't know if they have been replaced, Coils may be in the future. ) But at this point, It drives nicely, but I'd like to nail down what's going on in that suspension territory. Let me know if you guys have any ideas of what's going on.

[TheRoadShark]

Keep in mind that there is a possibility that it isn't the suspension at all. Something like a worn out / loose / wobbling driveshaft can have that effect, too.

[Royale240]

That's something I hadn't considered... What are some warning signs?

[Hijacker]

Check that all the air dams and your bumper are secured properly. A floppy bumper could cause annoying air flow issues at high speeds that unsettle the car.

[Royale240]

Alright, I'll have a go at my bumpers and air dams, see if anything is loose and needs some riveting / zip-tying. the car does seem to vibrate oddly at high speeds still, so I've ruled out the fluke status. I'll have to check out the drive line to see if there is anything noticeable.

[Royale240]

Bumpers are all attached well, there doesn't seem to be anything loose body wise on this car. Not sure what to look for on the driveline, could be something visibly broken, or a worn mount if it has one?

[TheRoadShark]

Common wear spots on the driveshaft are the U joints and the center carrier bearing. Sometimes the yoke on the tailshaft wears out, too. Basically, jack the car up, put it on jack stands, and move the DS around a bit. Twist it back and forth and move it from side to side in all different directions, make sure there's no play in the yoke or u joint bearings. Also make sure the center carrier doesnt have any excessive play, and the rubber isn't worn out. Or something like that

[Royale240]

Most Excellent! I will go ahead on get to it! I would definitely like to make sure There isn't anything going on down there, But my friends E30 M3 just had that same issue, Worn U-joint; even had similar side effects.
Having a feeling that may be the case. I'll get that car up and give it a good inspection! Thank you for your advice!

[nightheron]

The first thing to check out are your wheels and tire balance. When your wheel is on a tire balancer and spinning look to see if the wheel is wobbling around or spinning nice and true and check the balance. I've had the problem before and had to get a different set of wheels, it only happens at higher speeds, unless your wheels are really warped and tires terribly out of balance. Do this before you tear your car apart. Watch out for those curbs and pot holes. Good luck.