What should I look for when vehicle vibrates at speed?

It sounds like a stupid question, but let me explain.
Recently, after doing a cross rotation on my tires (due to a slight pull, after alignment) my Sportwagon began to vibrate a bit at speeds between 75-80mph.
The tires were checked and found to be out of balance.
Ride went back to normal for about 250 miles, when it began to vibrate again.
Another balance, normal, then again at around 200-250 miles same issue.
This repeated several times until tires were replaced for new set, and the issue still rears its ugly head.
Vehicle has 102,000 miles, wheel bearings feel tight (also no noise), suspension is tight (Koni yellows, H&R sports)[no play in upper strut bearings], tires are being road force balanced each time, tie rod ends feel tight (no play in steering).
When they go out of spec, they are 3/4-1 ounce off.
I thought that perhaps the tires are slipping on the wheel (Neuspeed RSe05), but the older set were not removed and had close to 15k miles on them.
Tires are Michelin btw. Older set Premiers, new set A/S 3's.
Vehicle tracks straight and true. Also @ 100mph it is smooth again. (though I'm sure the feds would frown upon my driving at that speed all the time)

alignment,

get the alignment checked. again. by someone who knows what is going on.

I had an alignment adjustment done, and went nuts blaming tires.

Bent rims. Tire pressure. Alignment. Ball joints. Slow down.

if you had bad alignment before you may have some badly cupped tires. I was dealing with a set of Potenza Grid tires tat had major shoulder cupping and they were not only the loudest tires Ive ever had but also vibrated and shook the car at all sorts of different speeds.

Maybe you're throwing a wheel weight (s). Does the person balancing your tires know what he's doing ?

I have had people use too fat of weights that scrape the front brakes. Horrible noises they should hear but twice I drove a few feet and knew they used fat weights. They did not hear the noise.

Wheels and tires should be turned on the car to look for runout. A friend had put replacement wheels on his car. Annoying vibrations. Tire shop could not figure it out. His oil change guy figured it out in a few minutes by spinning the wheels. Tire shop did not get the correct hubcentric adapters for the wheels.

meerschm said:

alignment,
get the alignment checked. again. by someone who knows what is going on.
I had an alignment adjustment done, and went nuts blaming tires.

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I'm going to have it checked again today. Will post results.

sprstu said:

if you had bad alignment before you may have some badly cupped tires. I was dealing with a set of Potenza Grid tires tat had major shoulder cupping and they were not only the loudest tires Ive ever had but also vibrated and shook the car at all sorts of different speeds.

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No cupping of the tires, they're brand new. Watching them spin on the balancer, no hops, just very smooth rotation.
The last balance done was after the machine was calibrated and road force balance was performed.

Went to the alignment shop this morning. They agree that there is a vibration, tires are balanced out, alignment is spot on. They say that it is most likely one of the motor mounts that is causing the issue. Stopped by the dealer for pricing on the mounts, just over $700 for all of them. Next step is to see which one if any of them are out of spec. Not sure how I'll be able to tell without pulling it out, or if someone else has had this happen (some advice).
To me it makes sense. Not something I would have thought about. I'll crawl under the vehicle later today when I get home and check the rubber in the few mounts I can easily reach for cracking or tearing.
I did have the dog-bone insert installed recently, only to pull it back out due to vibrations being a bit of a nuisance. Perhaps it caused the rubber in that mount to tear?

Put the dogbone insert back in. Vibrations appear to be a bit less than before, although it could be my imagination. It is frustrating, as I really enjoyed driving the wagon, now not so much anymore. Found today that the vibes appear most pronounced at 73-75mph. If I go below that it is smoother although doesn't disappear completely. Haven't had time to check the upper mount yet under the battery tray. Parked with the hand brake off, the engine rocks back and forth quite a bit when I push/pull on the vehicle. It moves more than our Passat does. (Probably apples to oranges as both vehicles are a bit different. Passat weighs more and has a newer TDI engine.)

Worn lower control arm bushings if this is worse under accellertion
Is the vibration in the steering wheel and not so much the rest of the car?
If so again LCA bushings.

redbarron55 said:

Worn lower control arm bushings if this is worse under accellertion
Is the vibration in the steering wheel and not so much the rest of the car?
If so again LCA bushings.

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I tried today to see if under hard accelleration anything changed. Not really, actually I felt less vibration, only when I backed off the throttle and settled into a steady speed does it vibrate again. I also feel it when I place my arm on the armrest. Tomorrow one additional thing I'll try is putting on my old set of 16" bioline wheels and tires to see if it makes a difference.
I also have a spare set of LCA bushings on hand and will double check the rubber inserts on the installed ones.

The LCA rear bushings are very difficult to diagnose visually.

last time I changed mine out, they looked just fine, but changing them out resolved the vibration in the steering wheel at a bit over 70 mph

andydg said:

I tried today to see if under hard accelleration anything changed. Not really, actually I felt less vibration, only when I backed off the throttle and settled into a steady speed does it vibrate again. I also feel it when I place my arm on the armrest. Tomorrow one additional thing I'll try is putting on my old set of 16" bioline wheels and tires to see if it makes a difference.
I also have a spare set of LCA bushings on hand and will double check the rubber inserts on the installed ones.

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Do this. It could be a warped wheel that is hard to see. Change the LCA bushings since you have them.

Donald

The only thing I can say is I looked for vibration with alignment, wheels, balance etc and it ended up being the LCA bushings.
The vibration is kinda because the toe in changes under poser and the excessive compliance in the LCA lets one wheel move right and the other follows and the pulls back setting up an oscillation left and right or is that right and left.
It seems to be in the steering wheel more than a up and down vibration in my case.
It is worth a try.

my old 16" bioline wheels vibrated like crazy at 70+ mph. ditched them for steelies and problem solved! they bent easily geez good riddance!

Changed out the front LCA rear bushings

On my initial test run at the same speed as before it felt smooth again.

Had a local shop do the work for me, as they were able to check the alignment at the same time. Had the tires rebalanced also for good measure, found that they were off by 1/2 ounce plus or minus.
Will check it again on the way home from work.

Total cost was $226.

For my OCD mind it is priceless.

Glad to hear that! I'm still on my original set at 237k miles.

Took a closer look at the bushings that were removed. Found this one was the worst with cracks when pushed to one side. The other one also contains cracks like this, but not as bad.

Not sure if I inserted the link correctly, as the image is not showing up.

good call on the bushings. The best way to inspect them is on a lift and look for the arms to not be centered and slightly crooked for the front lower arm bushings. The rears will show cracks

When I had my problems with steering wheel vibrations the bushings solved it and they looked perfect.