Real bad vibration ..flywheel maybe ?

Working on a 1985 Firebird 2.8 V6 for a friend. I'm stumped

It has a real bad vibration , rather it's idling or running down the road, its the worst at 1500-2500 rpms, and it "mostly" goes away at 3000+ Its bad enough that its not driveable IMO.



It doesnt act to me like a dead cylinder, a plugged injecter,bad motor mount, or something power related, it just seems like something is way outta balence.

Is there a chance the flywheel/flexplate is bent/cracked, or the 700R4 converter is goofed up ? It *seems* to shift ok........

Anything else to check ? The harmonic balencer isnt wobbling noticeably or anything..

Granted the 2.8 MPFI engine is a dog to begin with , but it seems to have full power.

Thanks guys,

Working on a 1985 Firebird 2.8 V6 for a friend. I'm stumped

It has a real bad vibration , rather it's idling or running down the road, its the worst at 1500-2500 rpms, and it "mostly" goes away at 3000+ Its bad enough that its not driveable IMO.



It doesnt act to me like a dead cylinder, a plugged injecter,bad motor mount, or something power related, it just seems like something is way outta balence.

Is there a chance the flywheel/flexplate is bent/cracked, or the 700R4 converter is goofed up ? It *seems* to shift ok........

Anything else to check ? The harmonic balencer isnt wobbling noticeably or anything..

Granted the 2.8 MPFI engine is a dog to begin with , but it seems to have full power.

Thanks guys,

If a clutch was just installed..it will be either the flywheel or pressure plate out of balance. Take it to a machine shop and they should be able to balance them together for you.

I would think that since the flywheel/flexplate is a precision balanced part that it would get worse at higher RPM. Since it has a 700R4 it has to be automatic. I would look into mechanical. Maybe a cylinder balance test is in order? While the car is running at an idle unplug each spark plug wire being careful to to shock yourself. Take note to RPM change or how the engine is running. Just a thought.

my dads 86 chevy blazer done that and his fly wheel had a crack in it.

I've had a broken Flywheel before, Literaly. On a buick omega. I did to many Neutral drops and shattered the Flywheel. I was able to tell that because at some point in time every now and then the car wouldn't start unless you pushed it a couple of feet by hand. Kind of funny isn't it?

DON'T DO NEUTRAL DROPS!!!!!!

I've had a broken Flywheel before, Literaly. On a buick omega. I did to many Neutral drops and shattered the Flywheel. I was able to tell that because at some point in time every now and then the car wouldn't start unless you pushed it a couple of feet by hand. Kind of funny isn't it?

DON'T DO NEUTRAL DROPS!!!!!!

i tore the rear end out of a camaro doing that back in high school

are you sure that the vibration is engine related?? I have a 91 firebird that had a road harmonics problem that worsened at certain RPM's as well. I replaced all of the old rubber bushings on the front suspension with polyeurothane bushings. What happens is when these rubber bushings wear out there is slack in the entire front suspension. make sure that its the engine before you go and drop the trans.
watersd1 91 firebird 383 sbc

So DONT drop it into neutral while in DRIVE right???? Because you helped me out alot!!! lol

transam ownr
a neutral drop is when you are stopped yuou rev up the motor in neutral and drop it into drive without taking your foot off the gas

unless you were being very sarcastic in that case im dumb

I have this exact same problem, just put in a new crate motor along with a new harmonic dampener and have the same vibration problem. it doesnt matter wether the car is in park or gear. Ive trouble shot all the same items as described in the upper posts, Ive also replaced the torque converter but not the flywheel.

is it possible to have an unbalanced crank or piston/crank assembly? Could I possibly have the distributor 360 deg. out and still have it run? Has the original poster solved the problem?

Any help would be greatly appreciated as Im out of ideas except to pull the motor.

sounds like the clutch is slipping or needs to be tightened. it might be engaging your tranny while idling. does it do the same thing in neutral or no?