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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.
Is it more prevalent under power at speed or coasting?
It's still there while coasting but more prevelant under load
Originally Posted by Turbomack
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.
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.
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.
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?
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?
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?
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.
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.
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?
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.
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.
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
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?
10-08-2019, 07:26 PM
Vibration at 75mph and higher.
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