Annoying vibration, no one has figured it out.

[pshirt]

Hi-

I have a problem with my 2004 GTP Comp G. It has an absolutely obnoxious vibration. I have been to 4 different shops and thrown plenty of money at it to accomplish nothing.

Here's what I know:

It doesn't matter if the car is in gear, it even does it when starting the car and idling in park.

I've had the engine and tranny mounts replaced, a couple of them twice. This did absolutely nothing to abate the problem.

The problem began last summer. I had the cat replaced in June and then found out the head gaskets were shot, so I had those done about a month later.

After the head gaskets were done, I noticed a very minor vibration only when launching the car from a stop. As time went on, it became much more noticeable and present all the time.

The vibration can be felt throughout the entire car. I was underneath last week while it was running, you can feel it in the motor, the exhaust, the body.

The more torque I'm pushing, the worse it gets.

Heavy acceleration gives my wife motion sickness with an almost cyclical feel to the vibration.

It's not the blower. With the belt off the vibration is still there.

 

One mechanic said it's possible that the pre-cat portion of the exhaust was somehow knocked out of alignment (he blamed the head gasket job) relative to the the rest of the exhaust so it is more or less in direct contact with the motor attached section of the exhaust, causing the whole body to vibrate by making the length of the system shake along with the engine. That's the only thing anyone has come up with beyond mounts and theories about a bad blower. I'll be honest and admit I don't know enough about the design of the car to say if that's even physically possible.

 

I'm at the point where I'm going to have to get rid of the car if I can't figure it out, it's an uncomfortable ride and the wife complains entirely too much about it.

 

Anyone have any more ideas?

 

Thanks

 

-D

Edited February 3, 2014 by pshirt

[rich_e777]

Maybe a loose or damaged rear exhaust manifold? Would put the noise/vibration coming off the rear off the engine around where the exhaust connects. I`d get back up under the car with it running to pinpoint the location.

 

Sounds like a bullshit answer the mechanic gave you, at least they could have put the car on a lift or stands and looked to see if it was actually the problem instead of just agreeing with a scenario. When a "mechanic" does this it would make me question their credibility.

[Galaxie500XL]

Stupid question, but how do the dogbones, and associated mounting brackets look?

[pshirt]

Stupid question, but how do the dogbones, and associated mounting brackets look?

 

They look fine, they were replaced in an effort to fix this.

[pshirt]

Maybe a loose or damaged rear exhaust manifold? Would put the noise/vibration coming off the rear off the engine around where the exhaust connects. I`d get back up under the car with it running to pinpoint the location.

 

Sounds like a bullshit answer the mechanic gave you, at least they could have put the car on a lift or stands and looked to see if it was actually the problem instead of just agreeing with a scenario. When a "mechanic" does this it would make me question their credibility.

 

I've been saying for a while that I thought the exhaust sounded louder inside the car. It definitely doesn't sound like the exhaust is leaking under the hood. It does feel like it's originating from that general area when i'm in the car. It was apart when the head gaskets were done, so it's possible he didn't torque the manifolds down enough or did some other sort of harm to it or maybe the piping it connects to.

[Imp558]

I wonder if something could have gone awry with the balance shaft when they were in there.

[Schurkey]

Does it in Park? Not transaxle, axle shafts, wheel bearings, or wheel balance. Could be torque converter, but unless it's thrown a balance weight (and they tend to be welded in place) I'd think this is unlikely.

 

Balance shafts? Maybe. I don't know anything about them, or how they're driven.

 

I'd look at the flexplate. A cracked or broken flexplate could certainly be a vibration source, might change intensity with applied torque, and could get worse over time.

Accessories could also cause vibration, but I'd expect that the frequency would be higher than what I think I'm understanding. For example, an alternator could get damaged and be out-of-balance, but I expect that would cause a VERY high-frequency vibration.

Edited February 5, 2014 by Schurkey

[55trucker]

Hmmmm.......after the heads were done did anyone do a cylinder compression test to see if you have one going along for a ride?