Terrible vibration at 20mph under power (1 Viewer)

[claiborne86]

Hello everyone, I have a 1996 lx450 that has been an ongoing project for the past year. I am going to list what is modified and recent maintenance. These will clear up the usual culprits.
Part time kit and Spartan lockers f/r
Full f/r axle job
Adj panhards
Ome 3”heavy
Metal tech rear control arms upper and lower
Delta radius arms
U joints
All tre and
Things I have checked
Hub play
Visual inspection of u joints
Re-torqued every fastener .
Greased everything.

Now to the symptoms. Vehicle develops a shake that starts at 20mph. It is very violent and persists until 40mph and the. Reduces some but doesn’t go away. It is hard to tell if it starts in the steering wheel or the seat. It is also only while under power. When you let out it stops. Tires are the damn Patagonia’s that are fairly new. Vehicle does have a fair amount of pinion play in the rear axle but I’ve seen worse without these issues. Caster angle on rear axle is perfect also.

Any helps or suggestions would be appreciated.

 

[robnicko]

Check the sliding joints on your driveshafts, either over greased and hydro locking, worn slip joints, old hardened grease.
Remove one at a time and lock centre diff to see if problem goes away in 2wd
or
Remove zirks from slip joints and see if it goes away, this will releive pressure if hydro locked - Note that removing the zirks will make a bit of mess though when the grease flicks out

Had a similar issue a few years back, symptoms very similar to what you describe (shook the seat, steering wheel & dash and dissapreared when backing off throttle) and the problem ended up being old hardened grease bunched up in the rear DS slip joint. I removed the DS, separated at the slip joint, cleaned out all grease, it was packed in and hardened like clay.. - If you do this make sure you mark your DS at the slip joint to ensure its put back the way it was
Upon installation what I did was fill the slip joint with new LMM grease then remove the zirk and unbolt from the diff. I then compressed the DS slip joint towards the transfer case to push out the excess grease and while compressed put the zirk back in. Then I extended it back to the diff, bolted up and has been trouble free since

 

[Rusty Marlin]

Check your phasing on the U-joints and propeller shafts.
Back in my youth I ripped a driveshaft out of my Dakota after changing the U-joints and got the phasing wrong.
Shook like you describe, I tried to turn around after a 1/4 mile test run and broke the yoke off.

 

[claiborne86]

Check the sliding joints on your driveshafts, either over greased and hydro locking, worn slip joints, old hardened grease.
Remove one at a time and lock centre diff to see if problem goes away in 2wd
or
Remove zirks from slip joints and see if it goes away, this will releive pressure if hydro locked - Note that removing the zirks will make a bit of mess though when the grease flicks out

Had a similar issue a few years back, symptoms very similar to what you describe (shook the seat, steering wheel & dash and dissapreared when backing off throttle) and the problem ended up being old hardened grease bunched up in the rear DS slip joint. I removed the DS, separated at the slip joint, cleaned out all grease, it was packed in and hardened like clay.. - If you do this make sure you mark your DS at the slip joint to ensure its put back the way it was
Upon installation what I did was fill the slip joint with new LMM grease then remove the zirk and unbolt from the diff. I then compressed the DS slip joint towards the transfer case to push out the excess grease and while compressed put the zirk back in. Then I extended it back to the diff, bolted up and has been trouble free since

Thanks man, I pulled the driveshaft and found a bad u joint that looked and felt fine until pressed out. Thank you for the responae