Shudder over bumps

[powderific]

I just picked up an 04 Ti with 55k miles that's nearly identical to one I traded off about 5 years ago. It's in really nice shape, for the most part, but it feels like it shudders way more over the bumps that my old one. Granted, it's been 5 years so I could be remembering wrong, but it seems extreme enough that I feel like I'd remember it.

The car looks to have the original shocks/suspension, and the tires on it are kenda something or others. The shudder feels pretty high frequency, if that makes any sense at all. Wondering if it could be shocks, bushings, tires, or something else entirely?

[barmato]

 What are your tire pressures set at?

[powderific]

OK, so, with any new car some discoveries. Turns out there are 3 different brands of tire on the car at various wear levels and they're all garbage bargain brands. I'd planned on flipping out to 15" wheels anyway. Guess I'll be doing that sooner rather than later.

That said, they're at 25 psi all around right now. Hadn't thought to check that.

Also drove it again and tried to get more of a feel for the shudder. Kinda feels like an echo of medium to big bumps, and where I really feel it is in the seat back and a bit in the steering wheel.

[barmato]

25 is a little low but shouldn't cause that.   I was thinking if they were way high. 

[thomsoad]

Turns out there are 3 different brands of tire on the car at various wear levels and they're all garbage bargain brands.

Ouch..tells me if he skimped on tires the PO probably skimped on EVERYTHING.
IMO You should change all fluids immediately and probably the plugs and accessory belts as well.
With 55K and 11-12 year old car I would start off w/coilovers personally.
Well after new matching performance tires obviously.

[powderific]

Yeah, I'm feeling a little let down right now as it LOOKED great and the dude was super nice, but yeah, not so great on the maintenance.  I did choose it over buying a new car and saved 10K or more in the process so I'm not doing too bad even if I have to do more maintenance than is ideal.

Tried to throw on my old snow tires to see if 15" wheels and known OK tires would help the shudder. Didn't seem to make much difference, but I also was only able to do 3 wheels since the third had four locking nuts on it with no tool. My attempts with bolt extractors have been fruitless so far.

Right now I'm planning on picking up some new 15" wheels and tires, along with coilovers, and hopefully that takes care of the crazy shimmy. The vibration/shudder is enough that it makes me nauseous after 20 minutes or so which is kinda crazy.

What coilovers do people like for non-track/daily driver use? I saw someone post about KYB AGX shocks with groundcontrol coilovers and fcm bumpstops, but I don't totally understands what specifically to buy and whether it requires some kind of setup when you get the stuff. I'm not looking for adjustability or anything. Not being a suspension expert, I'd rather it be something someone who knows what they're doing has already picked out. Also looking at packages from FM since it seems like an easy option.

[customcracka]

I had to use the socket-over-the-nut trick to get my stock wheels off.  The lock nuts were stripped and the tool wouldn't work.  I believe I used a 6 point 19mm and hammered it over the nut.  Then you'll need a vice to get the nut out and do the next one.  The craftsman socket worked better than the no name one that I had.  Once you get those things off, throw them away.  They're useless.

[powderific]

Yeah, I have a craftsman 6 point 19mm but couldn't get it hammered onto the nut. I definitely have no desire to keep them.

So, I'm trying to figure out what could be the main source of my ride issue before I start dropping money on parts. Driving the car is really unpleasant now and I want to do whatever I can to fix it.

Things that I thought of that could be wrong with it:

• Tires: they were cruddy and I have to get new ones anyway so this is happening. That said, the more I drive it the more I feel like it's not the tires, especially after trying it with my snows (which should be super cushy since it's summer and they're 15's)
• Shocks: They look fine and I've read that they should actually last to 100k miles easy, but if it WAS the shocks that'd be an easy solution it seems. I did not have any issues with the ride on my original MSM so I feel like buying something here would only help if it something is broken
• Alignment: Could this cause the issues I describe? I'm betting it needs an alignment regardless.

Am I missing anything that might be causing the issue?

[mr_hyde]

You will want the new tires/wheels and an alignment anyway so see if the shop doing that has anything to say about the vibration.  In the meantime, put the car on jackstands and roll the wheels over by hand to see if one feels or sounds different.  Grab the top and bottom of each tire and rock in/out.  Does it wiggle or clunk at all?  While it is up in the air (safely), start it and put it in gear.  Do you feel the vibrations (indicates related to the driveline and or rear)?  Also while up in the air, do you see any obvious damage underneath - especially to something that rotates like the drive line or a half shaft?

[powderific]

Ok, put the car up on jackstands and didn't have any weird stuff that I could feel grabbing at the wheels, and the underside is very clean with no obvious signs of damage anywhere. Didn't feel any oil on the shock shafts either.

Took it out on the interstate and the issue is more noticeable at speed. Certain sharp bumps seem to cause the shudder. It almost reminds me of when you're going down a washboard road only it tapers off right away. Kinda like driving an empty pickup or something. I almost feel better having had it out on the interstate because it feels like something definitely up and it's not just in my head.

I'm going to start with the new tires and see what the shop says when they have it up. Kinda want to wait on alignment as I'd have to do it again if it turns out I need new shocks. Thankfully I don't have to daily drive it till my wife's car finally kicks the bucket and I think it's still got plenty of life left.

[powderific]

Just wanted to update that I have the car in the shop for other routine maintenance and the guys there thought everything felt tight. Already ordered new tires/wheels anyway so they're going to put them on and see if it makes a difference. I don't think it'll fix this issue though since I already tried the snow tires and it didn't make a difference.

Found a guy on Miata.net who is having a problem that sounds exactly like mine and compared notes a bit. He did tires, shocks, and alignment before finally discovering that his control arm bushings were the culprit. The mechanics said the ranked on the wheels a bunch while it was on the lift and thought it was plenty tight, but I wonder if maybe they're not blown enough to make terrible noises and flop around but just enough to cause the weird bumping.

[powderific]

Sorry to keep bumping my own thread, but I have the new tires on with an alignment and the problem persists. The mechanics all thought the car felt fine, but none of them had experience with Miata's either. At least they're sure that nothing underneath is loose or what have you.

I really think it's the bushings. The quotes I've gotten to replace them have been kinda astronomical so I think I'm going to empty out my tiny garage so I can put it up on jackstands for more than a day and do them myself. Never taken on a project like this before, but it looks like it'd be within what I can do. Seems like it's mostly just super time consuming. Since I'll already have everything pulled apart I figure it's a good time to do coilovers as well. The car looks kinda silly right now as it sits super high in the rear, something like 14.75" fender to wheel center.

[Darth_Nuruodo]

I only have about a month and a half of Miata experience, but this wouldn't happen to be the trademark little wiggle that Miatas have from the chassis flexing around is it?

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[powderific]

I don't think so. It's pretty jarring honestly and I had one of these cars before so you'd think I'd remember it since it bothers me so much now. The more I drive it the more certain I get that it's not how it's supposed to be.

[SilverMiataRacer]

Get another Miata person to drive it.  Once your convinced there is a problem you will never be convinced it's not there.