I finished installing the rear driveshaft conversion kit on my 04 Discovery earlier today. Traffic finally died down enough to take it on a test drive at highway speeds and it has a really bad vibration starting at about 55 and continuing well into the 60's. I decided to get off at the next exit before something really bad happened. There is no noticeable vibration at lower speeds.

I'm sure I installed the spacer, and I torqued the the flange bolt down to 74 ft/lb per the AB instructions. I used my Milwaukee impact driver (max torque 125 fl/bls) to tighten the 3 of the 4 nuts on each end of the drive shaft. The 4th nut had to be tightened with a box end wrench but I cinched those down tight as well. I only now noticed that the AB doc says those should only be torqued to 35 ft/lb. I definitely intend to go loosen those bolts and re torque them to spec. Other than that about the only thing I can think of that might be causing this would be the "clocking" between the 4 bolts on the e-brake hub being off that of the rear differential. I'd bolted up the front end of the driveshaft first but had some difficulty getting the rear to line up so I jacked the rear off the ground and rotated the wheels and flange until the bolt holes on the flange lined up with the bolt holes in the drive shaft. I really can't see that causing the high frequency vibration I'm getting but thought I should mention since I know sometimes things get weird with rotating masses.

The pinion did wiggle a little bit when I tested it, but nothing crazy. It didn't wiggle at all if I put a little pressure on the nose of the pinion to push it back into the diff and tried to move it again, so I didn't think much of it.

Prior to doing this work there was a pretty mild vibration that came on at about 65, but nothing like this. I attributed it to the severely cracked rotoflex, which is why I bought the rear drive shaft conversion kit. To give a frame of reference to the vibration prior to this work, it was about as much vibration as I would feel coming through the seat in my '01 7.3L F-250 at idle. Sort of a slight buzzing coming up through the seat bottom. What I'm feeling now feels more like the time I lost some needle bearings working on a u-joint when I was a kid. The AB unit comes completely assembled so i'm sure *I* didn't lose any needle bearings in the U-joints

I'd like to get a plan of action together for tomorrow afternoon so I can get under there and get some things done before it gets too dark and cold. Where would you guys start?

 

Do you already have a new or rebuilt and freshly greased front shaft? (including the centering ball in the middle of the DC joint?) It seems odd that you have the vibration before and after a new rear set-up. Makes me think it might be something else which is why I'm asking about the front. Also did you grease the new joints in case they were overlooked from AB?

 

I did the front drive shaft about a month an half ago (including the Moog 6005 bearing inside the Hoykes joint). The vibration before was just a slight buzz. This is way more prominent. There was grease on the zerks for the new driveshaft but that's a good a idea, I'll add more while I'm out there.

 

Just got back from a test drive. This afternoon I loosened and retorqued the drive shaft bolts to 35 ft/lbs per the AB instructions. I also loosened and checked the new flange and I think that was the problem.

I think what happened was the flange wasn't actually fully seated on the pinion. I don't like hammering seals or bearing races into place unless there's absolutely no choice. I feel that the risk of damage to a seal or race is too high. Since I often work on my stuff late at night if ruin something I'm dead in the water, until I can get a replacement. To prevent this I like to use smooth even pressure of a screw and appropriate sized disc to draw the seal in by tightening the screw and letting the disc apply even pressure across the width of the seal. In this case I didn't have an appropriate sized disc to tighten against the seal to drive it in nice and smoothly so I improvised. I used the new flange and metal dust cover to get the seal started nice and square in the bore. I was then going to remove the flange, and use a hammer and a piece of PVC pipe as a drift to drive the pinion seal all the way home. I somehow lost track of what step I was on and ended up not doing that second part so when I tightened the flange to 72 ft/lbs it wasn't really 72 ft/lbs on the pinion shaft. The dust seal was pressing on the pinion seal which had some additional resistance.

Long story short; I used the pvc pipe drift to drive pinion seal home and then re-installed the flange and torqued to 72 ft/lbs. I know there's a difference because before I started work today the dust seal on the flange was just proud of the lip of the bore on the diff. After driving the pinion seal all the way in and then re-torquing the flange, the dust seal is now just below the lip of the bore on the diff. In total maybe 1/16 to 1/8th of inch more engagement on the splines of the pinion. A test drive after and the severe vibration is all but gone.