Drive line vibration

[Eagle Jeeper]

Hey guys I just got my jeep running again and did an "at speed" test run today and found I have a pretty good driveline   vibration when I step on the gas and it goes away when I let off.  SOme history I have an AMC 360\tf727\dana 300 setup with a double cardon joint drive shaft to the rear with the pinion pointing straight at the tcase.  THere is some play in the spines of the drive shaft I do have to get fixed.  Is that enough to give you a vibration.  THe drive shaft is custom I don't know if its been balanced or not should I get this done it was fabbed at the 4x4 shop who did some work for me.  I can almost guess that it not.  Why does it go away when I let off the accelerator.  Any direction or help would be good.

Thanks

[Mudpig97]

Murray get that driveshaft repaired and balanced then try it.  The amount of splines sticking out of that slip yoke will give ya too much play.  Not being balanced will also factor in.  Good to see you got it out of the garage.  There is more torque on the driveshaft when your on the trottle than when you aren't.  When you're off the throttle the rear end pushes back and it may be alot less plus the sloppy splines may staighten out more.  Once that guy repaires it properly you'll see a world of difference.

[Eagle Jeeper]

I thought as much.  Thanks

[hps4evr]

as well when yuo're in the gas the rear pinion will want to rise and cause some u joint mis-alignment. im guess you went with a spring-over set-up? cause if you did then ya might wanna look into a traction bar. off road if you get heavy with the skinny pedal you will find the rear springs will wrap and blow the driveshaft up. at leats then you wont have to worry about balancing it

[Eagle Jeeper]

SO if i understand right if i have a trac bar I don't need to balance my drive shaft.

[rangerdanger]

The driveshaft needs to be balanced or it will vibrate. When they set the pinion angle for the spring perches did they take into account that the pinion will rise under acceleration? that could cause a vibration too (having that trouble myself)

[red95jeepyj]

or your pinion angle is wrong or binding happened to me when my skidplate rusted out and my tranny dropped about 3 or 4 inches

[Eagle Jeeper]

I feel really good about the pinion angle and the axle wrap was minimal in the situation I was in I'm sure its in the drive shaft it was built too short and has some play I'm going to get it fixed up next week and we'll see whats what.