Vibration at 75mph and higher.
 

I have a vibration in the steering wheel and throughout the entire car.

I have had the my wheels and tires road force balanced at two different locations. Changed wheels and tires and roadforced balanced again.

I got the car aligned

Checked the wheels bearings

New rotors

New lugnuts



Checked for play in bushings and tie rods.

Jacked up the car up, put it in 5th and made sure the driveshaft wasn't out of balance.

Rotated the driveshaft 180 deg and rechecked in 5th on jackstands at 75mph

I'm at a loss of what to do next. I've been reading and reading and everyone swears that roadforce balance fixes the issue but that isn't it.

Thanks for your help

Is it more prevalent under power at speed or coasting?

I would check the alignment again. Then, I would check the torque on the motor mounts and MM to subframe and PPF bolts. Check for a bent or loose control arm while you re-torque stuff. Keep us posted on what you discover. I assume you checked the driveshaft U-Joints and your CV axle shafts. A failed U-joint in my 73 C3 was the last vibration problem I had to deal with but I’ve not heard much about them failing in a Miata, probably because they didn’t build them in the 70’s.

It's still there while coasting but more prevelant under load

I checked the axles and they are good. I forgot to add to my original post. I did check ppf alignment. It is 66mm.

Could old suspension bushings lead to these symptoms..?

I'm not sure. I'm not getting in loud clanking or creaking but that's not to say that they are not bad. I went through and checked them and they look clean and not torn.

There's no vibration with the car on jack stands/wheels off and drivetrain spinning at 75mph? What you describe sounds like my driveshaft balance problem (rotating driveshaft 180deg wouldn't affect the vibration BTW) but mine was there when on jackstands too. Hose clamp rotated every 45deg on front then rear of driveshaft let me figure out the best spot for the weight, now it's smooth.

That and pinion angle.

Just curious, do you hear a rhythmic squeak when you put the car in reverse and back up very slowly?

There is a vibration with the car jacked up at 75mph. The whole chassis vibrates so bad it's hard to pinpoint. I went under the car while my wife held it at 75 and the driveshaft looks smooth could it look smooth but actually be out of balance?

When was the last time you replaced the eccentrics?

Absolutely.

If it vibrates with no rear tires on, then you know it's not the tire balance or suspension. It's something that's spinning when it's on the jack stands...there's not many sources of vibration at that point.

Does it vibrate in neutral when on the jack stands?

Or, borrow a drive shaft that someone out your way has laying around to get that ruled in/out. The hose clamp idea is a good one too.

I haven't tried it in neutral while coasting down on the jack stands but on the road if I coast down in neutral from say 100mph to 70 it will vibrate the entire time. Which also leads me to believe driveshaft possibly related.

Update!

Got under the car today. Vibration still there but not as bad with wheels off. Still doesn't feel right. This is my 3rd NA all turbo'd with similar setups. Anyway I guess what I'm trying to say is that it is not a normal Miata vibration.

So I went under the car left it in 5th on idle and inspected the drivetrain and took my chasis ear with me. I can hear a knocking sound coming from the rear but with the chasis ear on the diff cover it sounds smooth.

So I keep looking and inspecting and I noticed the driver's side axle seems to appear bent as it is not as smooth as the passenger side.

Im thinking the driver's side CV might be bad. When I bought the car it had been in a small rear end fender bender and it was enough to snap the diff housing. I replaced the diff with a 3.9 since it was an open and replaced the passenger axle because when the diff dropped the bearings in the CV feel out and were missing.

Long story short. I think the accident hurt the other CV as well so my next move will be to replace the entire half shaft. First shaft in the video is the one I replaced. 2nd is the one in question.


Here are some pics of when I got it to how it sits today. It is a 97 with 89k mi

https://cimg8.ibsrv.net/gimg/www.mia...ef82d93d41.png
https://cimg2.ibsrv.net/gimg/www.mia...0b43b82b40.png
https://cimg3.ibsrv.net/gimg/www.mia...d7cbeaaf41.png

https://cimg8.ibsrv.net/gimg/www.mia...3877e3ac21.png
https://cimg1.ibsrv.net/gimg/www.mia...57591de690.jpg
https://cimg4.ibsrv.net/gimg/www.mia...4e04cb69d7.jpg
https://cimg3.ibsrv.net/gimg/www.mia...8434c6236b.jpg
https://cimg5.ibsrv.net/gimg/www.mia...605b0e7668.jpg

Have you pulled the driveshaft to rule out any sort of engine/trans issue? At least then you can positively isolate it to the diff or axles.

That CV is trash. You're on the right track.

I finally got around to working on the car. I replaced the CV and that helped a little but it was still there. SO I replaced the driveshaft and no it only vibrates north of 100mph. I also replaced all the bushings and wheel bearings and tie rods also ball joints. Then decided to put in steering rack bushings. Still vibrates north of 100mph. My previous na could hit 120mph smooth as silk, im beginning to suspect the 3.9 torsen

If the accident snapped the diff arm it’s possible it bent the rear subframe/differential mounts. Might just be a pinion/driveshaft alignment issues if they’re bent. Might try a known good subframe. They’re really not that robust on these little cars

I would think if the sub frame was bent I would have difficulty aligning the rear of the car, or installing the diff. Every thing lines up and installed smoothly.

Maybe. But it only takes a few degrees to mess with a pinion angle. Just something to consider if you can’t find anything. Did you actually have your driveshaft balanced?