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Vibration at starting 3,500 to 4,000 rpm setting still and or driving

Old 03-07-2019, 08:18 AM
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Vibration at starting 3,500 to 4,000 rpm setting still and or driving

Ok everyone im having issues figuring out this problem. I have a 97 firebird formula lt1 and I have a vibration starting at 3500 rpm to 4000 rpm and then smooths out and is more intense at 3900 to 4000 rpm. I have replaced both motor mounts and trans mount, I just replaced the clutch as wheel with a new flywheel and yes the vibration was there before the clutch was replaced but mine was slipping hints why I replaced it. I have replaced the harmonic balancer pulley, and i have run a misfire monitor while driving and reving to 4000 in neutral. I have checked spark plug gap and all im lost on this one guys i need some help..... Thanks in advance

Last edited by Dsharitz; 03-07-2019 at 08:19 AM. Reason: Spelling
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Old 03-12-2019, 01:49 PM
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Re: Vibration at starting 3,500 to 4,000 rpm setting still and or driving

Got you PM requesting help on this thread. Didn't respond earlier because you were jumping all over asking people on old threads if they figured out a similar problem, even though Shoebox and I told you the OP hadn't been on the site in years, and to post a new thread specific to your problems.

Let's start over.

When does the vibration occur? Does it do it with the car standing still, while revving the engine, with the clutch disengaged? Does it do it out on the road with the engine under load, clutch fully engaged? Or both? You imply both, since you checked for misfires under both conditions, but let's be perfectly clear.

Did running the misfire monitor (GM enhanced parameters count by individual cylinder?) confirm there were no significant misfires?

When you replaced the clutch, did you resurface the flywheel? Was the flywheel badly heat scorched? Was the pilot bearing replaced?

Was the old harmonic damper (it is NOT a balancer) damaged? Was the rubber ring connecting the inner and outer halves cracked, allowing the outer (pulley) ring to slip on the hub ring? Is there any wobble/runout to the damper, indicating a bent crank or bent hub? When you replaced the damper, how did you position it relative to TDC mark? Shouldn't make a difference, but worth asking.

Have you checked the motor mounts for damage?
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Old 03-27-2019, 07:38 AM
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Re: Vibration at starting 3,500 to 4,000 rpm setting still and or driving

Does with the car standing still, while revving the engine, with the clutch disengaged and engaged, while driving under a laod it does it as well. When i misfire monitored the car it was not misfireing at all and i checked each cylinder, i put brand new acdelco mounts on it (motor and trans), yes the old damper was damaged and i could spin it by hand but still the same vibration. Now i did have a friend who has an 03 cobra with the t56 and he said it seems similar to his issue he had, (twisted input shaft). i have had time totake my trans out yet to check but i will if you guys think i should soon. im just kinda at a loss and its almost race season so i really dont ant to take her down the track this way ... thanks in advance for any input
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