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Discussion Starter #1 (Edited)
Noticed some changes in engine vibration in the 1800-1900 rpm range that change with amplitude day to day. Today it is running exceptionally smooth so I decided to check the drive-line alignment. I dropped plumb bobs off three points in the drive train to check total alignment. I dropped one bob forward of the front crank pulley, the next at the forward end of the drive shaft and the third at the rear of the drive shaft. When I sight along the three lines the middle line at the forward end of the drive shaft is about 1/2" off of perfect alignment. My question is, does this make any difference in drive line vibrations being out on horizontal alignment? The vertical alignment is good. I occasionally feel something like a lifting mount somewhere if I let the clutch out too rapidly. Sometimes after some hard and heavy loaded runs the vibrations are more pronounced and then go away after several days of running unloaded. I don't see any evidence of a torn mount or loose bolt. Any ideas here?
 

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I had something similar in my 91 Dodge with the NV4500. I also noticed the shifter had more of a rocking motion whenever I shut the engine off along with the torque wind up when I left the clutch out. Problem turned out to be one of the transmission mount bolts had vibrated loose and stripped out the mounting threads in the tail housing.
 

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I originally installed the wrong depth throwout bearing. I knew that I did and planned on changing in a few weeks. The clutch fork was jammed against the face of the tranny. Two weeks later, 60 miles from home, the engine vibration finally caused some slack and it sounded like the tranny was going to climb out of the truck! FYI my engine/tranny/xcase are offset to passenger side several inches, only line back up with driveline out back.
Carl
 

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For shaft alignment I took a heavy camrea tripod and put the center tellescopic pole in the tripod from the bottom. Then I put my cheap laser level on the camrea mount so I can let it right down to the floor. Then set a tape measure up on the floor with the hook on the center of the pinion. Place the laser dot on the same inch mark as you have from the center of crank to the laser. Now all you need is to measure from the output shaft, keep in mind the output should be a bit high so you have some movement up and down with load and without. That movement should go below center as much as it will go above when fully loaded. The laser has took all the mess out of strings and eye balling. I've had soom of the best success that I've had driveshaft shops comment on how quiet they run.
 

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I think you guys are missing the point of drive line phasing.
If the engine is offset to one side the transmission should be square with it (offset the same amount). The output of the transmission should not be pointing at the rear axle u-joint if the motor has been offset. Some axles do not have the pinion in the center of the axle. This is no sweat for the u-joints. If the front of the engine is offset 2" then the transmission output shaft should be offset the same 2". We all know the pinion shaft is square with the axle. It is pointing straight toward the front of the truck. The idea of the whole driveline phasing is to make everything parallel. The same thing for the vertical alignment. If the motor is pointing up 5 degrees then the rear axle yolk should be pointing up 5 degrees. It has to be parallel. Sight an imaginary line down the center of the crank through the tailshaft of the transmission. Sight another imaginary line down the center of the pinion shaft. Those lines need to be parallel for u-joints to survive and not have vibration. If the engine is put in the center of the frame and the axle has the pinion in the center of it then there will be a straight line from front to back when viewed from the front. A u-joint will run better if it has a small angle in it than if it is dead on straight.
 

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excellent description of driveline phase. to add to it i hope . if you have ever taken a ujoint out of your tool box and added a six inch extention on each end when it is kept straight each end of the extension turns even and at the same speed all the way thru 360 degrees. now put a good bend in it and turn it one revelution you can see the ujoint parts speed up and slow down during one revelution . when two ujoints don't have matching angles they won't cancel each others speeding up and slowing down in one revelution. and it gives you a vibration and shorted ujoint life. if this was too confusing i am sorry.
 

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Discussion Starter #10
Thanks everyone for the input. I corrected the 1/2" of horizontal driveline misalignemnt at the rear of the transfer case. This fixed the vibrations I was experiencing around 1800 rpm. I also loosened the engine mounts and reset the engine down to make sure they were settled in correctly. The adjustments also fixed a shudder I had when letting the clutch out in second gear. I hate using 1st gear; it's such a granny gear.
 
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