70 mph vibration lt1

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Sep 20, 2012 | 04:32 PM

chris_14kingz28

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70 mph vibration lt1

i have a vibration in my car i have a 1997 trans am WS6 126k all stock motor. at 70 mph the car has a vibration. I can't see out of my rear view mirror.the vibration is worse when i let off the gas and decelerate. and from 0-70 it is smooth no vibration. It shakes the entire car. I thought it was the rear-end so i got a moser 12 bolt. still vibrates so i put a new drive shaft in the car and it still vibrated. i just went through putting a new clutch in the car. still the same problem i have no clue where to look next. the transmission shifts great i have had different shops look at it and they swear its not the transmission. i have took the tires and breaks off the rear of the car and drove it on jack stands and same speed it vibrates every-time.

i need some help of where to go next??

thanks chris

Sep 20, 2012 | 06:29 PM

Dave357LT1

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I'm gonna guess two outa balance driveshafts. Take if off and have it checked.

Sep 20, 2012 | 06:35 PM

chris_14kingz28

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I have a new spohn drive shaft and I have also tryed one out of a friends car that has no vibration and it still did the same thang.

Sep 20, 2012 | 07:17 PM

LilJayV10

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From: Evansville,IN

Have you tested it with the driveshaft out? I know that might sound stupid but that would eliminate the driveshaft/rearend.

What kind of motor/trans mount are you using?

Sep 20, 2012 | 07:28 PM

chris_14kingz28

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I've had 3 different drive shafts in it and it still vibrates and one came out of a friends car who don't vibrate at all Poly trans mount and factory motor mounts

Sep 20, 2012 | 08:09 PM

ale76051

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Do you have a T56?

Sep 20, 2012 | 08:12 PM

KFtransam

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From: Crown point, IN

Couldn't Hurt to check those motor mounts, have a buddy brake torque it a little "not enough to break the tires" while you check to see how much motor movement you have in the engine bay

If its moving more than a quarter inch or so that could very well be your problem

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Sep 20, 2012 | 09:01 PM

chris_14kingz28

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I checked the motor mounts and it don't move hardly any.. Yes it is a poly tranny mount and yea I have took the spacer out of it.. Still vibrates... This is not a tremble in the wheel this is taking a jack hammer and putting it under the car and at 70 mph turn it on and see how hard it can aggregate me.. and yes it is a t56

Last edited by chris_14kingz28; Sep 20, 2012 at 09:13 PM.

Sep 20, 2012 | 09:24 PM

#10

LilJayV10

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From: Evansville,IN

Do you feel it in the wheel or in seat?

Sep 20, 2012 | 09:25 PM

#11

chris_14kingz28

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In the seat

Sep 20, 2012 | 09:47 PM

#12

baycityrides

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wheel weight... i had this same thing happen in my old 6 banger camaro... i never thought it would be a wheel weight had moved... have them checked!!

Sep 20, 2012 | 11:58 PM

#13

ale76051

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From: DFW, TX

I had the same issue, it ended up being the 5-6 gear pack spinning on the output shaft. They're pressed on the shaft but come loose over time

Sep 21, 2012 | 06:41 AM

#14

chris_14kingz28

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the thang about wheel weights it dose it on jack stands with no tires in the car.. and when i run it through the gears 4th 5th and 6th are all in the 70+ mph range aould 5th and 6th make 4th gear vibrate

Sep 21, 2012 | 07:05 AM

#15

z_speedfreak

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From: limbo

stock tq arm mount? check that out

Sep 21, 2012 | 08:13 AM

#16

wrd1972

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From: Central Kentucky

OP,
Drive at 70MPH in 4th and note if the vibe is there. If its vibe free, shift to 5th and note if its there, Then go to sixth and do the same thing.

If you are vibe free in 4th but detect vibes in 5th and 6th gears only, you have T56 wear and tear so go here:
https://ls1tech.com/forums/manual-tr...vibration.html