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Old 09-27-2011, 06:23 PM
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rearend vibration

i have a vibration in my car somewhere and its really annoying! it sounds and feels like its in the rear suspension. changed all bearings and races except front pinion bearing! my factory upper control arms have been cut and shotend 2" and my pionion angle is way down is this where my vibration is coming from? i feel it at 2200 rpm and above in all gears. really bad in drive kinda vroom vroom sound like its something in a rotation. my drive shaft has been shortened also. i didnt have it done previous owner did. tranny is 350 turbo with 3500 convertor. need help with any info.

took motor out had a loose motor mount on engine but i dont think thats what it would be
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Old 09-27-2011, 06:49 PM
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Quote:
Originally Posted by 81malibuman
i have a vibration in my car somewhere and its really annoying! it sounds and feels like its in the rear suspension. changed all bearings and races except front pinion bearing! my factory upper control arms have been cut and shotend 2" and my pionion angle is way down is this where my vibration is coming from? i feel it at 2200 rpm and above in all gears. really bad in drive kinda vroom vroom sound like its something in a rotation. my drive shaft has been shortened also. i didnt have it done previous owner did. tranny is 350 turbo with 3500 convertor. need help with any info.

took motor out had a loose motor mount on engine but i dont think thats what it would be
Could be a number of things. Here are a few.

1. Bent Wheel
2. Tire/Wheel Balance
3. Bad/Worn Tire or Tires
4. Driveshaft not balanced
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Old 09-27-2011, 07:25 PM
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geometry ?

With modified arms have you checked center line angles, crank shaft-trans shaft angle vs pinion angle and the angles of the drive shaft . wrong angles will cause vibration.

Last edited by timothale; 09-27-2011 at 07:31 PM.
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Old 09-27-2011, 07:30 PM
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U joint phase ?

Shortened drive shafts have to have the U joints aligned, When I shorten a drive shaft I lay it on the work table and use a long piece of angle iron and scribe lines on the shaft and end yokes and make sure they are aligned before welding it back together. . If a factory drive shaft has a lot of balance weights from the factory balance process I won't use it to make a shorter one.
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Old 09-28-2011, 02:50 AM
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UCA's shortened 2"? Is it lowered that much?
Driveline angles are probably causing the problem.
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Old 09-28-2011, 04:06 PM
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yes upper control arms are shortened almost 2". they are factory ones also. really hard to change u joints unless turned a certain way to un bolt
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Old 09-28-2011, 09:19 PM
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Check your pinion angle. It should be parallel to the trans output shaft. If the trans output shaft is angled down 3 degrees then the pinion angle should be angled up 3 degrees. It sounds to me like you have your pinion angle set way too negative and that is where your vibration is coming from. You'll also be chewing up "U" joints on a regular basis with that setup.

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Old 09-28-2011, 09:26 PM
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I had a vibration around the same rpm in my chevelle and come to find out it was the drive line out of balance. But sounds like you have a lot more going on with modifications. Good luck and these guys gave you some great suggestions!
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