Vibration at speed
10-12-2007, 10:12 PM
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Vibration at speed
I need some help troubleshooting a vibration I have. I am not talking about a tire imbalance vibration but something I think is in the driveline.
The vibration first showed itself when I lowered the truck using 2" drop shackles in the rear. The vibration first shows up at 47 mph then mostly goes away until 60 and then gets progressively worse the faster I go. The 47 and 60 mph vibration is like a 60Hz frequency and then becomes a constant buzz as speed rises. At 100 mph (at the track of course) the entire truck is buzzing. I removed the drop shackles and replaced them with brand new stock shackles and bolts torqued to spec. Vibration still present. I swapped the engine and transmission and transfer case, not because of the vibration, and I had all four U-joints replaced and both driveshafts balanced. The front shaft was slightly out of balance and corrected while the rear was spot on. The Vibration unfortunately is still present. I really can't think of anything else that would be the cause. Hopefully someone out here has experience the same or similiar issue and been able to resolve it.
The vibration first showed itself when I lowered the truck using 2" drop shackles in the rear. The vibration first shows up at 47 mph then mostly goes away until 60 and then gets progressively worse the faster I go. The 47 and 60 mph vibration is like a 60Hz frequency and then becomes a constant buzz as speed rises. At 100 mph (at the track of course) the entire truck is buzzing. I removed the drop shackles and replaced them with brand new stock shackles and bolts torqued to spec. Vibration still present. I swapped the engine and transmission and transfer case, not because of the vibration, and I had all four U-joints replaced and both driveshafts balanced. The front shaft was slightly out of balance and corrected while the rear was spot on. The Vibration unfortunately is still present. I really can't think of anything else that would be the cause. Hopefully someone out here has experience the same or similiar issue and been able to resolve it.
10-12-2007, 10:32 PM
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OK I thought about that but didn't pursue it since I went back to the stock shackles. I also removed the 2 inch lift block that comes with the 4wd trucks but that shouldn't change the driveline angle I wouldn't think.
What should I be looking for for a maximum angle between the rear end and the driveshaft?
Any reason to check the front driveshaft? I can't think of one. The front end is higher than original since the new motor and transfer case is lighter than what I took out but that doesn't change the front driveshaft angle. The halfshafts are nearly straight also.
What should I be looking for for a maximum angle between the rear end and the driveshaft?
Any reason to check the front driveshaft? I can't think of one. The front end is higher than original since the new motor and transfer case is lighter than what I took out but that doesn't change the front driveshaft angle. The halfshafts are nearly straight also.
10-14-2007, 10:00 AM
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I lowered the front by taking the torsion bars down and the rear by removing the 2 inch spacer block and then 2 inch drop shackles. I have since removed the drop shackles so I am only 2/2 drop front and rear. It has been aligned twice since being lowered with the second alignment requiring no adjustment. Since I am RCSB I don't have a carrier bearing. I bought an angle finder last night and will be checking it today. I will post the angle.
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10-14-2007, 12:36 PM
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The driveshaft angle is 5 degrees and the pinion angle is 2.5. Based on the article posted above I think that my base pinion angle is positive. With the angle finder on the yoke I have to rotate it clockwise to get it to register 0. So I am thinking that I have 2.5 degrees of positive pinion angle. Could that be right? The thing is all stock supension other than dropping it 2 inches front and rear but that shouldn't have changed the pinion angle. If I were to switch back to the drop shackles the pinion would be nose down (not sure the exact angle) because the rear of the springs is placed in a lifted position within the chassis. What is confusing me is that the vibration didn't change after the switch back to the stock shackles.
10-15-2007, 12:44 PM
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A Member here "CHEVY6000VHO" Had the same thing. He did just drop shackles, picked up a vibration the he could NEVER get rid of. even after putting it all back to stock. ultimatley causing him to get rid of the truck. He tried everything, even a carrier bearing relocate, Good Luck...
10-15-2007, 01:22 PM
#10
Its in the working angles. 1* working is the target. Both ends.... not just at the rear. By changing the height of the rear end in relation to the end of the transmission it screws all the working angles up. I had the same thing. Wound up raising the rear of the tranny with spacers about 1/2" and think wound up with 2* shims in the rear.
It took 6 weeks of work, trial and error, to get mine mostly lined out.
It took 6 weeks of work, trial and error, to get mine mostly lined out.