Let's play: Name that vibration!

In reply to Robbie (Forum Supporter) :

It started at the end of the season. Thought initially it was just tires. Stock wheels weren't all that straight, and the race tires were pretty worn.  But when I started paying attention that it was always at the same speed then tried all the other tires I had. That led me to believe it could be the axles were just crappy cheap throw away axles. Changed those when I changed the rear calipers, all 4 rotors and new pads. No change. Brand new Konig wheels and Falken tires that balanced out phenomenally didn't change it either. 

So the "when" is a vague "late in the season" after many many track days and 10k street miles.

If it happens in a certain speed range regardless of accel/decel/coast the only candidates are the spinny bits from the diff to the tires. If it was aerodynamic you'd expect it to die down when driving in the draft of another vehicle. I'm also curious if it coincided with any part change. Running the car on jackstands and disconnecting one axle at a time (warning - this could cause transaxle oil to spill out, research first!) should be enlightening - it will either tell you which corner the problem is on, or if you can't reproduce the problem at all, hint at the issue being on the rear.

In reply to GameboyRMH :

I didn't have any part changes from may until late october when I swapped back to the stock suspension and brakes. 

I do remember the early second gen accents had the diff pin walk out and cut the case, but they didn't have any vibration that I can recall. 

This is why it's bugging me. All the "normal" things have been done/changed. But it persists. 

In reply to bobzilla :

You haven't changed the rear hubs yet but will? It could be those, if one is bent or something. 

In reply to Robbie (Forum Supporter) :

those are on the way. This weekend I was going to get the new race pads and rotors on the car, it's "just" 4 more bolts per side for them. They're OE and have seen more than a few abusive miles and a crap ton of heat from the rear brakes on track. Even if it isn't the problem, it's a good PM thing to do. 

Throwing something else at the wall to see if it sticks...

Are your wheels hub centric or lug centric? Any chance you have a bent stud throwing it off just enough to cause the vibration  

If the wheel bore is larger than the hub, getting a set of inserts to center them on the hub might be worth a try. 

In reply to No Time :

OE wheels are hub centric. Had two sets of those (before trading in the wifes car) with the same issue. All the racing wheels are all lug centric. Same problem. 

And to clarify more, the OE wheels have been cleaned of any corrosion and the hubs wire brushed to clean rust or dirt. If it's a hub, it's the hub itself being bent/out of round, but that should result in a constant vibration at all speeds that speeds up and slows down based on vehicle speed ... I think. 

This car has always been excellent at making me second guess things and throwing a monkey wrench in there occasionally

Calipers changed out? My Eclipse has the same issue and I traced it to a binding RF caliper. It also has a mild shimmy above 40.

In reply to cobra17 :

Rears replaced. Fronts move freely. This is speed specific to a narrow range. 

In reply to bobzilla :

i suppose if you had a bent hub, you would notice it as a brake pulsation after a few thousand miles, after the pads shaved down the high spots 180deg apart.

It's probably going to be something like the tires are finding a natural harmonic in the suspension or something and the system will get excited even if you have everything balanced and trued to the illionth.

Saturn L series had one of those.  65mph vibration that was part shudder and part gollywobble.  Replacing the vertical control arm bushings (aka compliance bushings?) with an updated part with a different durometer material was the Fix.  But Saturn would only pay for that after the customer bought four new tires and various other things, out of their own pocket, first.

I've been chasing a vibration that is sticking around through various part changes as well. I'm blaming lack of front end rigidity for now. Any chance a brace is missing a bolt somewhere, or the hood bushings are worn out? Shot in the dark...

Hood bushings? 

bobzilla said:

Hood bushings? 

yeah, at the pivot points of the hinges.

In reply to AngryCorvair (Forum Supporter) :

and how exactly would that 11lb piece off flimsy sheetmetal cause a vehicle vibration at 40-48mph? 

In 15 mins you can possibly figure it out or at least eliminate some stuff:

Get it on supports/stands

run it 

no vibration? It's on the end not turning (rear)

still vibrates?

look around while it's vibrating   
 

see anything weird? Fix it  

don't see anything?

start removing things - wheels, rotors etc 

repeat

In reply to jfryjfry :

Problem is I haven't had time since it got worse (tuesday). Monday was a funeral. Tuesday was cooking. Working 9 hour days on top of severe weather pretty much every day for the last 3 weeks isn't helping. 

What I've eliminated:

tires/wheels, tie rods, suspension (been changed twice with no change), rotors/pads/calipers, misfires and engine mounts. 

new hubs, still around. added G-Loc R12's and last years Porterfield R4(on the rear) pads back on with new rotors and some alignment tweaks. It's not that severe just annoying at this point. 

Did some catalog browsing and noticed the images for axles don't show a damper on the right axle on RA, but Kia shows one. 
 

Does the replacement axles you tried include the damper?

Image source dynamic damper

Lots of cars have a vibration in that range when the glue between the support ribs and the hood skin separates. Hows the underside of the hood look?

In reply to No Time :

The original one I removed I do not remember having the damper either. But neither of the replacements have one. 

In reply to Shavarsh :

its not the hood. 

Trying to help you out :) goodluck

This is a hard one, speed only would lead me to believe spinny bits like wheels and tires, but you've put multiple sets on. Almost every drivetrain issue I've been able to make worse or better through acceleration coasting or engine braking. Even hubs are generally affected by turning or braking. Engine issue wouldn't care about speed.

Have you put it in the air and shaken the suspension and steering down thoroughly front and back. It's a long shot but I've seen some weird vibrations I couldn't explain that were cured after replacing bad suspension components, but even then I've never seen them speed dependent. That's almost always wheels/tires or bearing related but I've always been able to make bearing worse or better by loading or unloading them

In reply to Opti :

Something I didn notice Sunday on track is shifting is slower. 2-3 and 3-4 you need to wait for the synchros to catch up. makes me wonder if this might be an internal trans issue starting to pop up. Or it could just be because it was 40* and cold.... 

And yeah I have shaken this thing so hard everywhere and came up with zilch. 

bobzilla said:

In reply to Opti :

Something I didn notice Sunday on track is shifting is slower. 2-3 and 3-4 you need to wait for the synchros to catch up. makes me wonder if this might be an internal trans issue starting to pop up. Or it could just be because it was 40* and cold.... 

could be a good lead, something on the output side of the transaxle, an output shaft bearing or maybe even a metallurgical or geometric issue with the shaft itself?  do these transaxles have any known issues?