Vibration
 

So ever since I acquired my 2002 Boxster S last year, I've been battling vibration in the steering wheel and what seemed to be coming from the rear of the car (entire chassis vibrating), and it is annoying the heck out of me! On the street, I use the OEM 18 in wheels with Michelin PSS. I also have a slightly more aggressive track alignment with -1.0 Front Camber, -1.8 Rear Camber and 0.15 deg Toe in Front, 0.25 deg Toe in Rear. There is no vibration or steering jerking when you touch the brake pedal.

Things I have done so far (partial list):

* Replaced the transmission mounts. Eliminated much of rear vibration from the chassis.
* Had all 4 wheels inspected, repaired 2 rear wheels that were slightly bent (0.035 and 0.060).
* Had one of the rear wheels gouge welded in and refinished. Looks like new.
* Had all 4 wheels Hunter roadforce balanced twice. This last time, the fronts did not even need weights, the rears were much better after repair. Vibration at highway speed is much reduced, but STILL not completely eliminated. Annoying!!!!
* Rear shocks were replaced when IMS/RMS and clutch replaced.
* Front shocks appear good.
* Control arms and bushings look good. Have not replaced any of them.
* New motor mount.
* Upgraded to Eibach front and rear swaybars.
* Added ECS tuning hubcentric wheels spacers.
* Added Rennline wheel studs.

4 things I can think of that could still be contributing to the vibration:

1. Alignment?
2. Older tires? (but this should be corrected during roadforce balancing)
3. Suspension bushings? Seems like they look good (no steering jerk while braking). Maybe it is only the rears then?
4. Axle shafts out of balancing or slightly bent?


Any time I go over 90 or so, vibration/shaking becomes much more pronounced, and I also get this weird buz noise? What the hell is that?

Thanks for any input or ideas you may have.

************EDIT**************

Car has 79K miles.
Replaced all 4 brake rotors and pads 1,000 miles ago.
Tires are worn and yes I should get new ones, but would they not balance out then?

I bet they aren't. I've replaced most of mine over this winter with the exception being the front droplinks.
I had the same vibration as you. Turned out to be a combination of worn control arm bushings and brake discs that had gathered material. The thing that made the biggest difference though was the control arms, vibration pretty much eliminated.

When we replaced them you could as near as damn it fold the bushes in half on the old ones, they were toast. if you just had a look at them though they were fine.

How the heck do you test these for wear whilst they are still on the car? Is there a testing method?

Nope, you can't. You can take them off to inspect but that's about it. The bushes on the arms should be solid, when they came off on my car you could EASILY move them around with one finger.

You didn't mention mileage?

When I had aggressive autocross alignment done (like yours as far as stock can go), on new Michelin super sports and ROW M030, it lost the 90+ smoothness. I think the camber and toe does it. I plan on going back to factory numbers one of these days.

You don't mention replacing tires after getting the various other parts and repairs. The tires may have been worn unenvenly which no amount of balancing can fix.

New brake rotors 1k miles ago.
So maybe I should look at the control arms...

Maybe go with a new set of tires and a good 4 wheel alignment. Balance of tire important but more importantly could any of the rims be out of round which no matter what will cause vibration.3000 rpm vibration is or was the motor mount. Disclaimer....Educated guess made from person who has driven down the same vibration road you are on. I dont think the tires are the culprit unless balanced incorectly but I think you said tires are do, so..... maybe start there, before control arms.Good Luck

Rotate the wheels+tires and see if the vibes follow??

Man you've done a lot of work to address this, but I think you've always suspected the tires. Old tires can do some strange things especially if the PO did unknown to you things like plugs in the tires. Road Force balancing will balance a spinning wheel even if the tire has uneven wear. Put it on the ground though and that square tire will not roll smoothly anymore (exaggeration for effect). A flat spotted tire can be balanced but will never roll smoothly again.

Treadwear does not affect ride smoothness unless it is extremely severe. Enough to make noise.

How old are your tires? Check the DOT dates & check the sidewalls & tread for cracking. If they sit in sunlight they get hard sooner, AZ sun will do that. :)

Just a guess since nobody else mentioned it yet: Flywheel? Stock or light weight? I have heard of some vibration issues with the lwfw.
Is it actually worst 90 mph, or is it an RPM range?

Holy crap, this guy will take his entire car apart at this rate.

To the OP, do the small stuff first like control arms and alignment before stripping the entire thing.

swap wheels
 

Have you got a friend with a Boxster/Cayman? If yes, swap the other car's mounted wheels for a quick check. If the problem goes away. get new tires for your car. If not, don't worry about tires and go after the other isues.

Stock flywheel (that I know of...). I haven't replaced it, but had cluth, IMS, RMS replaced and my mechanic said flywheel looked good.

I get progressively worse and you increase speed from 75 mph to 100+.
Mostly steering wheel, but you also feel it in the floor.

Alignment won't cause vibrations

wheel out of round is easily achieved by hitting curb once. Vibration gets worse with speed in my case.

I just had all 4 wheels inspected and the 2 rear straightened (.035 and .060).
Then all 4 wheels/tires were Hunter roadforce balanced.
How would a reputable shop (Wheel Specialists, Tempe, AZ) verify that the straightening was effective? I would think without the tire mounted, but I didn't ask or witness it.

Unless extreme, I would tend to agree that alignment would not cause vibrations.

Well there is the problem.....if it is vibrating then it's not straight.It is probably much better butt....Did I miss the post where you mentioned having the 2 rears straightened? High speeds low profile tires on a preformance based platform you wheel feel it so much more even if only off a little. sometimes budget restraints steer people to straighten. Got someone to loan a set for diagnostic purposes as mentioned in a previos post? I would gladly loan mine but my left rear is off a little as well.

I see where you mentioned the bent rims in the original post so I did miss it. IKO look no further than the wheels. Human eye cannot see the deviation.

New wheels typically need 1/4oz weight to balance them, I would guess despite Wheel Specialists best efforts your rear wheels require a full 1oz just for the bare wheel.
Before debuting a unknown wheel on your car, always have it spun on a balancer & observe the up & down "hop", as well as the side to side movement to see what you are dealing with. Especially with new wheels since often they are non-returnable if a tire has been mounted.

Well today I went back to the tire and wheel shop to have the wheels checked again for out of balance. I've been battling the same vibration issue at 70 mph and higher.

The shop says all 4 wheels roadforced balanced less than 10 lbs and all is good as far as the wheels are concerned. So that leads me to believe that the suspension or steering is the culprit. Since I've observed no slop in the steering at all, and it is very crisp, I believe the LCA bushings or balljoints must be worn.

I have not replaced any suspension components other than the rear shocks after I bought the car last year. Front shocks rebound fine, no leaks. LCAs look old. Any way to tell for sure? If I do LCAs, should I also do the track arms?

You'll probably find that the tuning fork bushes are worn and tbh there's no real way to just visually check them. When i replaced mine the old ones "looked fine" but you could virtually bend them in half with very little effort at all.