Well many good points have been addressed here.
As far as rotors and drums go in vibration diagnosis, there are 2 differnet vibrations you can get..a vibration caused by an out of balance or a vibration caused by excessive lateral run out (apply pulsation).
When describing a rotating vibration, any componant that rotates at the same speed as the tire and wheel assembly can cause a "tire related" vibration.
Brake vibrations are usually called pulsations, they occur when the brakes are applied.
Brake vibrations are caused by excessive lateral runout of the friction surface.
Lateral runout can be caused by improperly torqued lug nuts.
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The rotors were turned at 9000 miles due to braking vibration. Then at 16,000 they were replaced for a braking vibration.
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The reason for this was improperly torqued lug nuts and a pulsation occurs 3000-6000 after the lugs were tightened.
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The intermediate drive shaft on these units cause the drive line to shimmy no matter what you do. If you go to a 1 piece drive shaft the problem goes away.
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Some GM light trucks come with a 2 piece driveshaft, the working angles and phasing must be dead on to prevent vibrations.
Some of these concerns have been eliminated by installing a 1 peice driveshaft.
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Guys that have put spring assist or Air Bags on there truck that were suffering from this vibration have said that after the Air Bag or Spring Assist is installed the vibration goes away
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Some of the vibrations may be related to a launch shutter or spring wrap up.
By changing the suspension geometry, you can change the frequency of a vibration (the vibration is still there, just at a different speed or intensity)
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I have a vibration in my truck that begins right on acceleration at about 20 km.hr.
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This could be a launch shutter and by changing driveline angles it could be eliminated.
The pinion nose rises as the truck is excellerated this causes the driveline angles to change, by lowering the pinion nose 1/2 degree, you could eliminate the concern.