High freq.vibs after rear uni replacement.

So I have no lift in the rear,new tires,truck had a nasty vib at 57mph.pass seat waving type of vibration.no noises,just shaking.rear uni was notchy so I replaced it.didn't remove center support,just unbolted flanges and removed rear part of the shaft.marked the flanges and out it on the bench.turns out it was a beast,frozen caps and corrosion.yea it was fun.when I was fighting the joint the slip yoke did come out.I put it right back in, but I'm not sure it it was in the correct spline......after that I market it and just removed the yoke and replaced the joint.now I marked the flanges,but with all the wrestling I lost my rear most mark on flange going to the third member.had the mark on the flange at the cb so I know it's good,but the rest is just a mess.NOW I have a high freq.vib around 40.like a tickle really,can feel in gas peddle too.so should I rotate just the third member flange?disconnect both the flanges and rotate the whole rear assembly 180*?

 

If you got the slip yoke close, you can run a strung to see if all the yokes line up.

 

If you got the yokes backward from what they were before, yeah you may have extra vibes, and rotating may help

 

It can't be off that much,i was holding the ds and the yoke at the same time when I pulled it out.I will pull a string on it 22morrow evening to see if the flanges are out of phase.

 

Take a hammer and tap the flange and shaft all around the new ujoint caps to release any tension on the ears that happened during the joint install.

Drop the whole shaft and take it for a drive. That will isolate the issue to the shaft, which it is 99% likely to be. But you can also be more sensitive to the vibe since you are watching for it, and it may have been there prior.

What brand ujoint did you install? If zerk on the cap did you install it so that the zerk is in line with the slip yoke zerk and cv zerks? Are you positive that you got the snap rings in completely?

 

Skf uni,zerk is on cap,not sure about alignment.the vib I have been fighting is strong shaking at 57mph.this is like a tickle through the steering wheel and pedal.off and on.this is a learning curve for me,i will pull it in this evening and check my mounting flanges to see if both are in line(bolts straight up and down)

 

You can see where the shaft originally came in contact with the flange. Should have some sort of stain or marking from its original location.

 

Ok so I talked to my local shop.he had me check my phasing,seems the rear (at the slip yoke)is out of phase with the front.if so just by one spline.when I crawled under there,the rear is flat(ears on each side are inline with axle shafts. the yoke at the bearing are not flat(tilted to one side).will pull the yoke off and align as good as I can this evening.I'll check uni for tightness while doing this.hope this works......

 

Ok so after phasing in the rear yoke,still vibes continue........I'm going to rotate the whole assembly 180* 2morrow evening.the joint seems to be in correctly.all caps are seated properly,not over tight,moves without any notchyness.like the one I removed.but I will say this,if this next attempt doesn't work it will be going to my local guys.I have done these repairs before,but the trucks that I usually work on are not in as bad of shape as this unit.

 

Worked on it a bit today,seem rotating the third member around did the most.I disconnected the flange at the bearing and rotated it 180*...no change....I reset that and while I had it disconnected I pulled the slip yoke(still attached to third)rotated it 180*...no change....reset that back....but I disconnected the third to reset it,while I was there I rotated the third to line up with next set of holes.90*I guess....I did notice at this time the rust that stopped the flange from seating 100%flat.....now I didn't clean it with my grinder at this time I just tighted bolts up real good.....his made the biggest change yet.don't get me wrong on really smooth pavement it is still there.but I'm making progress....thank God too....I am going to clean the thirds flange and rotate another 90* and test some more 2morrow...

 

Finally just sent the whole ds off to have it balanced.I added a new center bearing to avoid them telling me it was that.it didn't change the vibs either....Well they said all joints are good,csb is good and all the shaft needed to balance it was double yoke,off csb turned 180*.........I still feel something,but I got the bypass and truck will travel 75mph with 2 fingers........next is the rear diff cover...