Bad vibrations

[F5Chaser]

I have this posted over on miata.net but I thought I'd try to get some local feedback.

I have an 05 with 96k miles. New brakes, new wheels and tires(TR C1M with S Drives) and new shocks with the original springs. Alignment was done a couple weeks ago using FM specs. Between 68ish to 80ish I get a horrible shaking/vibration from what feels like the rear end. The steering wheel doesn't do any shaking but I can feel it in the seat. No abnormal noises, no pops, creaks, moans, and handling doesn't feel compromised.

The problem is, the shaking isn't consistent. I can drive on the same stretch of road 2 different times and get 2 different experiences. Does it on asphalt, concrete, new and old...some of the time. The new shocks are Sensen, which I know are crap, but the car is acting the exact same on those as it did on the original shocks with 95k miles on them and at least one of those were totally dead and blown. I've done the same speed in different gears and get the same result. Not thinking it's driveline related, but I'm not an expert so I can totally be wrong. I tried to see if there was any play in the hubs and my untrained eye couldn't detect any. Felt very solid on all 4 corners.

In a couple of weeks, I'm getting Koni's and FM springs installed. They may help, they may not. Before I start throwing even more money at it(bushings, driveshafts, axles, C4, 5.56, etc), anyone got any ideas that I can at least look into pending the install of my new suspension?

Thanks.

[jrj512]

Maybe try swapping the wheels around to see if the issue follows one. That would at least rule them out.

[sammm]

Check the ball joints and A-arm bushings.

[Robert]

Did it start after you changed the wheels/tires? I am thinking 1 or more of them may be out of balance or out of round. With a tire that’s out of balance/out of round it takes some time for them to find the right conditions to setup a resonance and start shaking.

[Jim m]

Did it start after you changed the wheels/tires? I am thinking 1 or more of them may be out of balance or out of round. With a tire that’s out of balance/out of round it takes some time for them to find the right conditions to setup a resonance and start shaking.

I struggled through two sets of tires, and 35 thousand miles of inconsistent shaking with our motorhome (it seldom shook on rough roads, always on smooth ones). Several of the wheels were slightly out of round, and so was at least one tire. I just replaced the front tires (one tire was nearly 1/8 inch out of round, one wheel was 1/16 inch out) at a shop that took the time to match the tire to the wheel. After a few minutes effort both tire/wheel assembly had less than 1/32nd run out. Just put about 300 miles on it and the shake is gone. Who wouda thought less than 1/8th inch run out on an 18,000 pound car would matter.

[OZMDD]

I agree with moving the wheels around to see if the issue moves. Out of round wheels can be tricky to find, and the variable may be that it is present in two wheels, so they only do it when they are resonating with each other, as Robert mentioned. If you have OEM wheels/tires, throw those on. If you need to borrow a set for testing, I have several. You are welcome to spin by and swap them, your tr1's will be fine as collateral. :)

Bushings and ball joints are also likely culprits.

[sammm]

The inconsistency is why I don't think it's tires/wheels....hopefully I'm wrong.

[F5Chaser]

Wow. Getting more help here than on the big forum. Thanks!

OZMDD, I pulled off OEM wheels with Dunlop's last night. Same symptoms with the OEM/Dunlop's as with the C1M's/S Drives. I rotated the OEM's around every time I had them balanced and had the same inconsistent issues. Haven't moved the backs to the front and fronts to the back with the new ones yet. Have only had them for less than 24 hours. That's tonight's project.

Robert, It's been ongoing for several months. Replaced the shocks, didn't help, replaced wheels/tires thinking bad wheel/tire, didn't help.

Sammm, I'm with you about the wheels/tires now that I have brand new ones and have the same issues.

With 96k miles, bushings wouldn't be out of the question. There's just a lot of them to replace at serious $$$ from what I've seen.

[Keifersmith]

Just play this while you drive and it'll all even out...

[F5Chaser]

HAHAHAHA. Yeah, that works. I'll do that on the way to work in the morning and report back.

[Rogue]

Ill find it when I get it up, off all fours.
Should have ask me to drive it when you were here.

[F5Chaser]

Ill find it when I get it up, off all fours.
Should have ask me to drive it when you were here.

Yeah, I probably should have but sometimes my brain doesn't work right. I think when I learned that I wasn't getting another free Jake's burger, that altered my mental state.

[F5Chaser]

Sitrep.....drive into work this morning, same road, same time of day, same speeds, no vibrations, no wiggles, nothing. Was able to do 70-80 all the way. Only difference I can think of is temperature. It was around 30ish when I left home. I didn't make any changes to the car. Hmmm.....