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Discussion Starter #1
rear drive shaft,

driveshaft has been shortened and spun balanced to 3k rpm by a reputable shop, put on a sterling 10.5 from an 05 sd a while back and have never been able to go past 65 mph without a very fast/fine vibration almost like a cell phone set on vibrate.

it is throttle sensitive, as in if i let off the throttle at 60, the vibration will start and then go away when i give it gas, and return if i go past 65.

to the best of my ability,

i checked the angle of the transfer case shaft which read -3 degrees, driveshaft was at 15 degrees and the pumpking was a +5 with three leafs in the pack, sitting on the factory ford 3" blocks sitting on my shop floor which is pretty flat but anyway.

i made a set of custom 2 degree wedges with a hole in the center and inserted it between the leaf pack and the 3" block with the larger end of the taper pointing torwards the front of the vehicle which then put the pumpkin at +3 degrees (in other words i had to lower the pumpkin to get it at positive 3.

now the vehicle vibrates at 45-55mph and smooths out at 60+mph then vibrates again past 70.

i've tried many different angles, even dropping the pinion an additional 2 degrees to conpensate for axle wrap but still did the exact same thing and its driving me nuts because i can't drive my rig down the highway and have to go slow so i don't ruin something.

can anyone tell me what i'm doing wrong? ive read article after article on pinon angles and how to set them up, it is a single driveshaft, as in single cardan setup.

it runs best with no shims or anything of the sort under the leaf packs and when the tc pinion is at -3 and the pumpkin is at +5. it still vibrates but will start to vibrate at 65 while pushing the gas and vibrate if i let off the gas until the rig slows to around 55 or until i blip the throttle and take out the vibration.

i'm totally at a loss on what to do next, could my angle finder be off on the tc since there really is no good way to check it?

from what i've read almost all vehicles are set up with a -3 degree engine downward angle which would put the tc angle right at -3 degrees which is what i get on my angle finder, my rear end with the 2 degree shims puts the rear end at exactly +3 degrees which would make it 0 pinion angle......correct? and still vibrates. what am i missing????

u joints are super tight, no weights have flown off of the shaft when they balanced it yet, axle came from a running truck that had no issues with vibrations at all.:cry
 

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I scrape on both sides
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just curious, when was last alignment and tire balancing? had a similair vibration pattern going before i balanced my 33's
 

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Discussion Starter #3
the truck has been this way after several alignments and two sets of wheels and tires and tons of tire balancing which is another topic........these km2's for some reason just don't balance out.

i want to build a set of latter bars but don't want to make them until i figure this vibration out first.
 

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I scrape on both sides
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well, the driveshaft could still be balanced, but put in upside down... just something i was taught in a junior college ford program... so who knows if/ they know what theyre talking about or not
 

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is it possible, that who ever put ur u joints in got a needle bearing out of place i had this happen befor on a s-10. a needle bearing came out and went into the luberication hole and caused a minor vibration at high speed. just a thought. good luck
 

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Discussion Starter #6
they did keep the joints strait as in both are parallel with each other.

does the yoke going into the transfer case only go one way? as in there is a special slot? i had it marked with a crayon when i removed it but when the cut and welded and re-balanced the shaft the marks were gone that i made so i had to guess where the yoke goes in AND guess where the driveshaft bolts to the rear end.............will and can those make that big of a difference?
 

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River rat,

You ever find the issue?? Have been fighting a vibe issue myself.
 

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This a great article on drive shafts: http://www.pirate4x4.com/tech/billavista/PR-shaft/index2.html

I have not been able to stop a high speed vibe in the rear drive shaft of my F150 since switching to 4:11 gears (it's spinning faster now). It got better when I got the angles on the u-joints within 1/2 degree of each other but it is not satifactory. I am going to install a drive shaft with a double cardon joint to eliminate the vibration and cut down the angles on the u-joints. I will need to add the angle shims to get bring the pinion up. In reading the article, the u-joint life is cut in half at the 5 degrees which is what they are currently running. It just makes sense to set-up a double cardon shaft. I also have not had the vibration issue with that set-up in the past. There are some obvious benefits to raising the pinion with a double cardon u-joint even if you only wheel it lightly.
 
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