Ok ,I'm at witts end here ( what little I have left) with what I will discribe as a driveline rotational vibration . Here's how eveything started , noise from rear at 160,000 , no issues prior , tore rear down and found bad pinion and carrier bearings scored , replaced all bearings and reassembled rear to specs. While I had the rear driveshaft out I replaced both u-joints . All parts are correct . Drive truck @55mph driveline vibration . Try to isolate better ,remove rear drive shaft ( while rear end is on jack stands ) and start and put in drive , notice vibration from front half of rear drive shaft where the suppoort bearing is located , good ,finally making progress , install new support bering and u-joint in front half of rear drive shaft , test drive , vibration has diminished but still there. A mechanic buddy of mine suggested that the driveshaft may need to be balanced , but what I have a hard time believing is that is the problem . Also I checked brakes , rotors, and front driveshat and everything is ok. Is there something else that I could be missing ??

 

do all u-joints move freely by hand

 

Yes , all u-joints are ok . I had some concern about one of the new ones that I installed , so I replaced it again and still no change , something else is going on but I just cannot put a finger on it .

 

just wondering if you have any updates on this issue....i have recentyl had all my unjoints replace and rear pinion seal replace by a mech....he said everything looked good but i get a slight vibration at 40 mph to about 60 mph and goes away....took the truck back to him and he said tires are out of balanace....but had the tires rebalanced and vibration is still there...bout to take it back to the mech and see if he can fix

 

The first place I would look is your lift (although it is mild). What happened to the driveline angles? Did they tilt the rear pinion up when they did the lift? This is not necessarily a good practice, but seems pretty common.

If you have u-joints at both ends of the shaft (not CVs), and the angles on each of the u-joints are not identical (or very close), you will get torsional vibe.

If you do a lift, that puts more angle on the top u-joint, and sometimes people will rotate the pinion upwards to avoid lengthening the driveshaft. This reduces the angle on the pinion u-joint. This is a sure recipe for torsional vibe. A GOOD driveline shop or a GOOD 4wd shop that does lifts will know this.

 

good point, but would the vibe just now appear after new u-joints installed. i am actually wondering if the mech. might not have aligned the two d.shafts properly. would that make a vibe.

 

Oh, sorry, overlooked that. But absolutely, the two ends of the shaft need to be "in phase" in order to cancel the u-joint torsional vibe. I think he would have only messed that up if he separated the slip yoke (does it even have a slip yoke?) and put it back together out of phase.

But maybe it is more likely you have a balance problem.

 

yeah its got the slipjoint. is there any way i can pull it all apart and rotate it till its right again.
balance problem is another thing i was thinking about. where can you go to get it rebalanced and approx. cost.
Thanks for the info!

 

the slip yoke should have a key tooth and only go together one way
if there is any wear in slip joint it can also viberate

 

guess that eliminates the slip yoke....could it have anything to do with installing the rear pinion or the barrings??

 

could likely be a needle laying in bottom of u-joint cup

 

After you put the ring and pinion together did you check the gear lash? What about bluing the gears to make sure that they are meshing properly?

 

i didn't put the pinion together, a local mech. did that for me as well as replace the u-joints.

what does bluing the gears mean??

 

Bluing is used durig a machining process to check for highs and lows. When you put the compound on the gear theeth then turn the ring and pinion a few times you will see how they are lined up. If the Pinion is in to far then the Outside of the Ring will remove the bluing (= excess wear) on those parts, if the Pinion is to far in then the inside of the Ring will remove the bluing, and if the Pinion is in the correct position then it will be right in the center. That is while shimming the Pinion during install. When installing the Carrier/Locker it needs to be shimmed left to right (drivers to passenger side). The bluing compound will just show a little bit of rub-off on the edge of the teeth if the ring isn't fully engauged; if the bluing is almost all gone then the ring and pinion are set to tight together. I don't have any pictures of what I am talking about, but it is illustrated in a Haynes manual. Another way to test if the Ring is set the right distance from the Pinion is to feed a strip of newspaper inbetween the two: If the news paper gets ripped then it is too tight, if the news paper gets creased it is just right, and if the paper doesn't crease it isn't tight enough. As for the backlash it should be set between .002" and .004" if I remember right. You put an indicator on a tooth of the ring gear then move it back and forth to check the slop in the gear mesh. Any good mechanic should have done this right. Since they were re-installing the same ring and pinion there should be no issue if they reused all of the same shims. Sorry for the long post. I hope this clears things up.