Miata front end vibration

Hey all. Not the usual at 60 or so vibration, which goes away shortly thereafter, but sustained vibration throughout the rest of the speed range. It doesn't really ever smooth out, just seems like the frequency of vibration gets higher with speed.

Wheels were recently "road force" balanced, whatever that means, and that didn't do it. Wheel bearings still feel tight (just replaced them a while back).

Alignment recently redone to add some caster back in - had used the FM 5 degree figure, it's now 6.5, and that helped a little, but it seemed to move the vibration point higher in the speed range.

My thoughts are that it's a ball joint - yeah or neah? What's a good method to check them? My thoughts are that since caster helped a little, likely the uppers - but I might just replace all of them if it's likely its a ball joint.

Help.

Jack up car, put your hands on the wheel (still bolted to the car) at 3-o'clock and 9-o'clock and yank one hand then the other, your looking for lateral play in the tie rod ends there. Now put your hands at 12 and 6 and do the same thing, basically wiggle the tire real good. 12 and 6 is to check ball joints. This is a basic check for any car. Oh also, do you have wheel spacers or anything? You can also try removing the wheels and taking a wire brush and clean the mounting surface off the wheel and the hub, I've seen enough rust/corrosion build up that the wheel won't sit flat and even if it's balance will still vibrate at speed

Right front was where I felt it (while a passenger), so I did the wheel test, everything is nice and tight. Maybe I'll try a little more effort, really wobble it hard.

Mounting surfaced are clean (AZ), no spacers.

To make sure it's not the tires, rotate them front to back.

Keith Tanner wrote: To make sure it's not the tires, rotate them front to back.

Will do - but would a problem with the tires present on a "balancing machine"? Just recently balanced/rebalanced ("hunter road force" balanced, I have no idea if that's better than "regular" balancing)?

Or not necessarily?

If youve got a shifted belt, flat spot or the tire is out of round, it could balance ok weight-wise but still cause a vibration because its not, you know, round. I have this issue with my current set of tires due to flat-spotting them with over aggressive braking at an autocross. But i would have thought road force balance would catch that.

Road force balancing puts a load on the tire (I believe) and should spot things like out of round or belt problems. But it's still really easy to swap the wheels around to make sure.

Road force balancer are awesome. However, like normal balancing, you still need a tech worth a crap for it to be done right. A quick swap front to rear will confirm if it's the wheels/tires or not.

Here's a short video on road force balancers. http://youtu.be/DQxVAssnbp8

Is there a noticeable wobble if driven at 5 mph? Driveshaft or rear axle work performed lately? Any work done to car prior to this problem?

Do you feel the vibration in the steering wheel or the seat? At what speed does it start?

So I finally got around to rotating the tires, and it definitely appears to be that - with the switch, I still get the vibration but it's coming from the back half of the car.

Thanks all.