Drive line vibration

[72GMC51]

I have the truck together and have test driven it several times, the problem is a vibration that seems to get worse the faster I go. Had the drive shaft balanced and new joints installed. How would you check a two piece drive shaft angle, I thought because it was two piece that the rear end trany angle did not matter because of the carrier bearing, if this is not right how do you set the angle since the drive shaft flexes in the middle. Also any ideas as to what might cause the vibration, I lowered the truck 3" in back and 2" in front installed sway bars on both ends and had a eaton posi with 4:10 gears installed and I have 700r4 trany (which I am having issues with getting the TV cable adjusted properly).
Thanks
JC

[mbgmike]

you can run the motor without the driveshaft attached and run it up to driving rpms and see if it vibrates. if it does run it without the trans attached and see if it still does. it could be an unbalanced flex plate.

[69 longhorn]

A driveline "vibe" can make you nuts chasing it (been there). I agree, that the 1st thing you need to do is decide if its in the shaft, or the engine. If you can rev the eng in park or nuetral, & feel the vibe, its in the engine, or flexplate/converter. if thats the case, i would mark the converter & flexplate for location, then unbolt the converter & push it back from the crank.start it up..... if you still have a vibe, you know its in the flexplate, or the engine balance. if the vibe goes away, you need to try indexing the converter to a different spot on the flexplate, & bolt it back up(you have 3 spots on a chevy to try). If you dont find the Vibe in the engine, its time to play with the d shaft. The front 1/2 of the shaft should be pretty much straight off the trans output shaft(you might go about 1/2 degree to work the grease into the U joint). the rear 2 u joints need to egual, but opposite angles. from there, you need to know that the 4.10 gears that you added spin the shaft much faster @ any given speed than say 3.07 gears, & if there is a little problem in the shaft it will be more noticeable. One trick old rodders do, (assuming alll the above checks out), & the balance is good on the shaft.....unbolt the shaft from the rear diff, & rotate it 180 degrees ,& bolt it back up. it doesnt make a lot of sence.......but sometimes this helps. Best of luck, 69L

[jhwkns]

are you sure it's not the tires?

[69 longhorn]

Originally Posted by jhwkns

are you sure it's not the tires?

Yes, that is very possible, that problem could be in a tire, or an axle 69L

[Big Block]

I had a bad rear axle bearing that was causing vibration. I had the drive shaft balanced, install a new engine and trans and still had vibration. A bent rim or out of balance tires can also cause vibrations. Good luck tracking it down. B.B.

[MrC1]

My experience has shown that a vibration like yours that just can't be found by the normal initial means (DS checking, bearings, tires, etc.) always turns out to be the pinion angle, or u-joint angle. Since you said you just lowered it, the liklihood is even greater.

[86swb]

I had the same problem once and come to find out it was a bad tire. I was lucky. That was the first place I checked.

[masterbeavis]

soemtimes binding the bearing cap on a ujoint will cause vibration (read improper installation) When you take the driveshaft off, twist the cross, if it is really tight, the caps are pressed in too tight.

[72GMC51]

I have not had much time too work on the 72 I am getting my newest ride 94 GMC 1/2 Extended ready to take a ride to Chicago to look at a 91 z28. But I did run the engine up through the rpm range in nuetral and I can feel the vibration not as bad but its there. Thanks for all of the replies.
JC