Vibration at 2500rpm - Neutral or Driving

[Damon03Termi]

Hey guys,

My 14' GT recently developed a weird vibration through the whole car. It feels like the driveshaft is unbalanced.

It's around 2500-3k rpm and only when the cars warm. In neutral just revving up, or driving. The car seems to be running and driving fine. Just shakes as you're around 2500rpm and quits after you're above 3k.

A few people mentioned their cars did this from their exhaust. I've taken all of my exhaust off and just started the car with open headers. Vibration was still present.

Recently installed a new driveshaft and installed a VMP last year. Car only has 6k miles on it and maybe 500 on the VMP setup.

 

[Mojo88]

Your post is a tad confusing... you say it "It feels like the driveshaft is unbalanced".... and then you later say, "In neutral just revving up, or driving". So the first big question is: does it vibrate when the car is not moving? If so, then that totally eliminates driveshaft issue.

Of course, the very first thing to do is confirm engine is running properly. Any CEL's or other indications of engine issues? Maybe start by taking plugs out and doing compression check, examining plugs, etc.

The rpm's you mention (2500 to 3000) are right in the sweet-spot range of engine vibration, which I've had too many times. One engine I rebuilt (big block Chevy), I had the race shop balance the engine, and switch from external balance to internal balance (involved adding some Mallory metal to crank). The engine vibrated exactly as you described. I checked everything I could, made sure all cylinders were firing properly, and it still shook when I revved the engine. I thought it might be the clutch.. nope. I had to remove the engine and take it all apart, send back to shop, they re-balanced and it still shook, then I did whole process again and went to participate in the balance job, confirming all the bobweights were correct and so on. Anyway, when we spun the crank assembly, it was WAY off on the balance. Once we got it smooth on the balance machine, I put it back together and it was fine.... smooth as silk again.

I'm only telling you the story so that you realize I've had balance issues and am familiar with them.

Bottom line: assuming your engine is running properly; my guess is that your vibration issue is located in clutch area or damper. A piece of clutch disc could have been blasted off, especially since you're making more power now... or damper may have shifted. I'm not an expert on your particular damper, so maybe someone else can chime in how to check it??

 

[Damon03Termi]

Your post is a tad confusing... you say it "It feels like the driveshaft is unbalanced".... and then you later say, "In neutral just revving up, or driving". So the first big question is: does it vibrate when the car is not moving? If so, then that totally eliminates driveshaft issue.

Of course, the very first thing to do is confirm engine is running properly. Any CEL's or other indications of engine issues? Maybe start by taking plugs out and doing compression check, examining plugs, etc.

The rpm's you mention (2500 to 3000) are right in the sweet-spot range of engine vibration, which I've had too many times. One engine I rebuilt (big block Chevy), I had the race shop balance the engine, and switch from external balance to internal balance (involved adding some Mallory metal to crank). The engine vibrated exactly as you described. I checked everything I could, made sure all cylinders were firing properly, and it still shook when I revved the engine. I thought it might be the clutch.. nope. I had to remove the engine and take it all apart, send back to shop, they re-balanced and it still shook, then I did whole process again and went to participate in the balance job, confirming all the bobweights were correct and so on. Anyway, when we spun the crank assembly, it was WAY off on the balance. Once we got it smooth on the balance machine, I put it back together and it was fine.... smooth as silk again.

I'm only telling you the story so that you realize I've had balance issues and am familiar with them.

Bottom line: assuming your engine is running properly; my guess is that your vibration issue is located in clutch area or damper. A piece of clutch disc could have been blasted off, especially since you're making more power now... or damper may have shifted. I'm not an expert on your particular damper, so maybe someone else can chime in how to check it??

Sorry, I was only comparing it to driveshaft shake. It does it sitting still.
No CELs yet. I think I’ll start with plugs. I had been thinking damper or clutch/flywheel but didn’t want to dig that deep into it if I didn’t have to.
Hopefully I don’t have an issue like yours. I had a Paxton on before the VMP and maybe my damper or clutch has just had enough in this short period of time.

 

[Mojo88]

Sorry, I was only comparing it to driveshaft shake. It does it sitting still.
No CELs yet. I think I’ll start with plugs. I had been thinking damper or clutch/flywheel but didn’t want to dig that deep into it if I didn’t have to.
Hopefully I don’t have an issue like yours. I had a Paxton on before the VMP and maybe my damper or clutch has just had enough in this short period of time.

You won't have an issue like mine. Now, if someone had just rebuilt your engine and installed new components, then I would totally suspect you might.

Anyway, it's a wise move to look at plugs first. I would also do compression check at that time. Use the old "Occam's Razor" principle - the solution to most problems is usually the simplest, most obvious explanation.

Hopefully others will chime in with suggestions. Good luck!

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[Damon03Termi]

You won't have an issue like mine. Now, if someone had just rebuilt your engine and installed new components, then I would totally suspect you might.

Anyway, it's a wise move to look at plugs first. I would also do compression check at that time. Use the old "Occam's Razor" principle - the solution to most problems is usually the simplest, most obvious explanation.

Hopefully others will chime in with suggestions. Good luck!

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thank you for the help. I appreciate it!