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Old 07-22-2011, 10:46 AM
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bad vibration while driving

I have a 81 malibu with a new 400 a 350 turbo with a 3500 stall 4.11 gears when i start accelerating i feel a vibration in my car it feels like its in the back part of the car it starts at like 1500 rpm and when im in 3rd gear between 2000 n 2800 it really gets to vibrating i can feel it in my seat and it vibrates in the rear package tray. it goes away a little at 3100 in drive. if i stop dead in the road n stomp it and go through the gears i dont feel it. it very annoying. it did this prior to me installing my new engine. i have since replace motor mounts 2 new harmonic balancers. this car was raced before i got it and it looks like the pinion angle is angled way down from where it should be. any help would be appreciated thanks

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Old 07-22-2011, 02:32 PM
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Got the right flywheel on it? 400 is external balance.
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Old 07-22-2011, 02:34 PM
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Quote:
Originally Posted by dgcantrellsr
Got the right flywheel on it? 400 is external balance.
X2 could very well be the problem.
Have you checked the u-joints ?


Cole
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Old 07-22-2011, 03:27 PM
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Cross member

Is your rear transmission mount good? Have you or anyone else ever jacked the car up using the rear transmission mount or crossmember as a jacking point?

First, check to see if your rear transmission mount is good. If you have used the transmission mount or crossmember as a jacking point, you bent the crossmember and the drivshaft angle is now incorrect. Go to a frame alignment shop that has eye bolts cast into the concrete floor. They will chain the crossmember down to the floor using the eye bolts and then jack the car up by the proper jacking points and pull the crossmember down and back in the correct angle to the rear end.

A common symptom for the problem I outlined:

The car has a vibration that starts about 40 to 50 MPH and gets worse until about the speed reaches 80 - 90 MPH then the vibration suddenly diminishes and the ride is smooth again. The vibration diminishes because at 85 MPH or so, the body has risen high enough to bring the driveshaft into correct alignment with the rear end. That seems to be a common problem with 1964 through 1970 GM A-body vehicles when the crossmember is used as a jacking point.
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Old 07-24-2011, 06:28 PM
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i found out my upper control arms have been shortened and boxed if i put the factory control arms on it wont that put the angle of the pinion where it needs to be
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Old 07-24-2011, 06:32 PM
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Quote:
Originally Posted by 81malibuman
i found out my upper control arms have been shortened and boxed if i put the factory control arms on it wont that put the angle of the pinion where it needs to be

You need to check your pinion angle and see where it's set at now..
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