Wait, when you said you tried two different sets of wheels, we assumed rhat wastwo different sets of tires as well. From your latest comment rhough it sounds more like you had one set of tires that was mounted on different sets of wheels.

That lets you mostly rule out wheels (but not fully, since you said there wassome change from that. What if both sets of wheels have one bent one? Stranger things have happened). But of course wouldn't rule out tires if its the same set remounted. In fact it implicates the tires...

 

I really doubt with all the changing and swapping that it is the axles, but wanted to note that a known good set of OEM's may vibrate if installed in a car sitting at a different ride height (changing height can move the bearing surface to the edge of the already worn in area causing some vibration). But again, with all the swapping around and no change I doubt it is that. Just FYI there.

So the one other thing could be the driveshaft. That would be independent of wheels/tires and axles and would still occur with the clutch in or out. I would expect the joints in the driveshaft to vibrate more under load than not much like an axle CV joint, but could do it all the time as well. Could also be out of balance as well due to some sort of damage, but that should be apparent (big gouge in it or something similar).

 

overdue update-Still no progress!! Checked all diff mount and subframe bolts, all were tight to tq specs, didn't find anything loose. Swapped in a known, good driver side hub with no change. Rotated tires around again and tried adjusting tire pressure to both high and low end. No change, lower tire psi might of been a little better/smoother.

To clarify, I have tried 2 sets of wheels and tires, One set of PF01's with 255 Federal rsrr and a stock set with regular kuhmo tires. The PF01's are worse, but rotating them every way imaginable produces the same vibration(even rotated the lug nuts!!). Even running stock wheels in front with the PF01's in back produces more vibration. But I think it's not the wheels causing it, but just amplifying the vibration somehow. I'm going throw the stock back on and see what it feels like. Kinda coming back full circle.

The vibration did get worse after a full track day. Happens in the same conditions but just much more noticeable. Got another track day a week from today, maybe I'll just break whatever is the cause and finally know what it is!!

To Recap:
Parts Changed: Both driveshafts, driver side hub, stock wheels and tires, PF01's 255 square.
Set up change:high psi, low psi, rotate tires (front back, side to side, forwards and backwards), rotated lug nuts.

Running out of ideas!! I guess next would be to focus on the diff and driveshaft. Driveshaft has no play and no damage. Diff I regularly change fluid (using Motul gear comp 75w/140). Might be tearing out the diff soon? Open to any and all suggestions/ideas! Thanks guys!

 

Think I figured it out! I unhooked the rear swaybar (just removed one endlink) and it made a dramatic difference. A little backstory, I had the car corner weighted (ohlins on the car) and the tech said he coudn't get it perfect because the stock swaybar endlinks were too short and binding. I never got adjustable since the cross weights were good enough for my needs. It hit me that they might still be binding and preloading the bar some way causing an odd harmonic vibration. Lo and behold, with both rear wheels at full droop, the passenger side endlink needed about half inch of compression to get it out and in. Something may be bent to cause this to, but isolating the swaybar just about cured it. Ordering some adjustable endlinks tonight and we'll see if that cures it for good!

 

thanks for the update.

 

New update:still chasing this issue. . After further review, disconnecting the swaybar hasn't eliminated the issue, nor has installing adjustable endlinks.

Swapped in a borrowed differential and still have vibrations. Last thing on the drivetrain would be the propeller shaft.

Car has ohlins r&t and cycled all four through the adjustment range. Nothing weird. Setting them softer than they had been showed on improvement either.

Also replaced the other wheel bearing and hub. No change.

Car has a cr wing mounted to a cr trunklid. Might try removing the wing. Grabbing at more straws here.

 

Transmission related?

 

is your pinion nut on the diff loose? that's what caused my vibration.

 

Make sure your sub frame bolts are tight and get an alignment. I had my S for almost a year now and I thought the car just loves to vibrate at high speed. My new Sienna van ran smoother 100+ mph and so did my wife's BMW, you never thought you were going 100+ on it. But I have always had vibration on the S for just going 80+. Thinking the car being 14 years old will be prone to vibrations. Anyways I tried many things, changed wheels, tires, coil overs, change diff, diff mounts and motor mounts. These made improvements with handling and removed some clunkiness it had, however it still vibrated at high speed. My next step was to change out some of the bushings but they look good and show no signs of rattle on uneven roads. I even had alignment done once when I got new wheels, and then again when I lowered with coil overs. Last month I had an oil change and my service guy mentioned my front right tire are wearing badly. Wow 6 months and I am out of alignment already? I am not even sure if this is normal for this car. So 2 weeks ago, I installed rigid sub frame collars and noticed some of the sub frame bolts were very easy to remove. So I am thinking that tightening the sub frame bolts and getting wheel alignment helped smooth my car out. I feel much more confident going over 100+ now. I am no expert but this has been my experience and I am not even sure if torquing the sub frame bolts are part of maintenance.

 

Are you using wheel spacers? Possible tires have been flatspotted? You can remove wheels and let them roll and easily see if they 'bounce' or pull to a side while rolling