Phantom Vibration

[AnarchyVA]

I bought a 2003 Cobra about two months ago. It had roughly 24,000 miles on it when I brought it home. Ever since I have experienced and been chasing down a vibration that I do not recall when test driving the car. Likely because the excitement of the looming purchase clouded my ability to pick up on fine details.

First observation of the vibration was on highway trips between 55 and 70 mph. The steering wheel would shake, the mirrors would shake. The vibration was rhythmic in nature. In this mph range the vibration would amplify every several seconds then decrease after another few seconds. Repeating itself for as long as you were traveling in that mph range.

Initially I thought that the vibration must be coming from the wheels/tires because the dealer, at my request, swapped from the unimpressive satin stock wheels to some larger, staggered, black wheels and tires after I test drove it. However since then I have had the front end aligned, had all four corners road forced balanced, and replaced the two flat spotted front tires with brand new rubber. Additionally I have checked for play in the front end associated with bad tie rods and bearings and there is nothing. The vibration, although slightly less, still exists. So I no longer believe that it is related to the front end or wheels/tires.

My latest observation of the vibration is during idle while in neutral. What I once blew off as just an inherent characteristic of the Terminator I now believe is a symptom of my problems. This vibration is also rhythmic in nature. From some online research I have narrowed down potential problems to a harmonic balancer, vacuum leak, dirty MAF and possibly even a compression issue in one or a few cylinders.

Does anyone have any experience with similar vibrations? Vibrations that are rhythmic in nature, are felt at idle while NOT in gear and also most noticeable at highway speeds?

 

[c6zhombre]

These cars are VERY sensitive to tire/rim combos and highway speed vibrations are common. Verts even more than coupes.

What size tire and rim are the staggered blacks? Make and model for both rim and tire? Did you not keep the factory sized satin silvers?

Wheel bearings also fail on these cars...so make sure they're not going out. Jack the car up, wiggle the tire by hand and see if there's any play.

 

[AnarchyVA]

These cars are VERY sensitive to tire/rim combos and highway speed vibrations are common. Verts even more than coupes.

What size tire and rim are the staggered blacks? Make and model for both rim and tire? Did you not keep the factory sized satin silvers?

Wheel bearings also fail on these cars...so make sure they're not going out. Jack the car up, wiggle the tire by hand and see if there's any play.

Well again, I've had the tires/wheels road force balanced and replaced the two front tires that were flat spotted with brand new tires.

And the vibration is also felt at idle when in neutral.

I no longer believe that the vibration is coming from the wheels/tires or the bearings.

 

[c6zhombre]

Well again, I've had the tires/wheels road force balanced and replaced the two front tires that were flat spotted with brand new tires.

And the vibration is also felt at idle when in neutral.

I no longer believe that the vibration is coming from the wheels/tires or the bearings.

I know, I read your post. I have serious doubts your idle vibration has anything to do with your highway vibration. It doesn't matter if you had those tires road force balanced or not...."cheaper" tires or rims, even brand new, can create issues. These get magnified on a vert. And the colder the weather the worse it will become.

I had an '04 vert for 4 years before I bought my coupe...it had the same vibration you are describing. Same speeds. Mirrors would shake. Some of it you're going to have to live with, it's a 14 yr old circa 1979 chassis vert....it will almost go away in hot summer temps. It wasn't until I bought a set of $$$ CCW rims, that are aircraft quality aluminum made in America, that most of the shake finally dissipated.

Too bad you don't have the 100% stock setup to at least compare against.

 

[AnarchyVA]

The reason I tie the two vibrations together is due to the rhythmic nature of both vibrations. At first I was convinced that it was something in the front end. My primary focus was on the wheels/tires since I had them swapped. However after ensuring the geometry of the front end was correct, the tie rods/bearings were solid, the wheels were true and the tires were replaced I don't FEEL that the problem lies so much there. I may certainly be wrong. Clearly I am not certain of the root cause. But due to the similar rhythmic vibration occurring when the car is not moving and the transmission is in neutral, my gut feeling is that there is something going on in the engine area that is creating a frequency in the chassis that is magnified when traveling within that mph range.

To answer your question the wheels are these. 18" x 9" in the front and 18" x 10" in the rear.
https://lmr.com/item/SVE-1007FD/200...rm=1100004968841&utm_content=All SVE Products

Tires in the front are:
Bridgestone Potenza Pole Position S-04
275/35/18

Tires in the rear are:
Bridgestone Potenza RE760 Sports
295/35/18

 

[c6zhombre]

Well, tough to say for sure. If you want to dig deeper....you'd need to look at flywheel, clutch, driveshaft, pinion angle. Also the indexing on the driveshaft. Change out the bushings, etc....maybe try iridium plugs to reduce engine movement at idle. NGK TR6IX, or run ethanol lol

But I've seen people go though a lot of that list looking for this phantom...and come up with less than 100% success.

Good luck with it

 

[AnarchyVA]

Yes, I'm trying not to just throw money at the problem. I was able to justify the alignment, new tires and balance as they were good to take care of anyways.

I'm going to have to look deeper into other areas. Unfortunately the cold weather is keeping me from wanting to.

Thank you for your help.

 

[hotcobra03]

If you feel vibration sitting..

engine mounts

Aftermarket clutch

 

[AnarchyVA]

If you feel vibration sitting..

engine mounts

Aftermarket clutch

I may be wrong.....but I don't think it is either of these either. The engine has VERY little movement, there isn't any clunking that I can detect when going in or out of gear and the vibration exists when the transmission is out of gear.

I haven't yet determined what causes the trend but I have noticed that the vibration, while in neutral and idling AND when driving at highway speeds, is less noticeable at times and obnoxious at other times.

 

[MG0h3]

Ive had exhaust do weird stuff like you are mentioning. Make sure it isnt touching anything.

 

[MalcolmV8]

I've had many wheel and tire vibrations over the years on various cars and never has it been in a rhythmic motion like how you described. The closest I've had was a wheel bearing once that would flutter in and out of vibration depending on how the tire was loading up on it.

A quick google search for rhythmic vibrations while cruising seems to indicate driveshaft as the most common culprit.

Curious as to what you find.

 

[big dad]

Based on your description of a vibration even at idle I would suggest you check the spark plug boots for any evidence of spark arcing through to the cylinder head bore. You can't see it unless you inspect each one out of the car.

When I was a tech I ran into this a couple of times, and every time the complaint from the customer was a vibration, when in fact it was a misfire. Additionally, if you bought this from a dealer chances are they washed the motor and water got into the plug wells.

It's just something to check, after all if you don't know where it's coming from or being caused by, find out where it isn't coming from.

 

[hotcobra03]

I may be wrong.....but I don't think it is either of these either. The engine has VERY little movement, there isn't any clunking that I can detect when going in or out of gear and the vibration exists when the transmission is out of gear.

I haven't yet determined what causes the trend but I have noticed that the vibration, while in neutral and idling AND when driving at highway speeds, is less noticeable at times and obnoxious at other times.

These engines are extremely heavy than add t56..

mounts are cheap in cost and dont last long.

its hard to check mounts on a stick but I noticed on mine the blower belt cover was hitting hood...when I was working on engine for other reasons, both of mine were broken..

From ford they are cheap..

another area. ..stock lower pulley bushings

these dry out...causing stange sounds and feel at 1500 to 2500 rpm..

I also had found noise from abs module ,, bolt was missing and bracket was rattling almost like an exhaust rattle againt metal would change to rpm