Berlina driveshaft followup (long)

["Watry, Andrew (LNG-SFR)" <Andrew.Watry@domain.elided>]

A couple people asked me to follow up with information on the driveshaft
problem I was having on my 2000 Berlina from a couple weeks ago, so here
goes.

Problem: 

The specific problem was that a had a flutter or rumble only when very
lightly on the throttle at freeway speed (above 50 mph), neither pulling
hard, nor coasting against the gears with throttle closed.  The problem
exhibited itself only when not really accelerating or decelerating, but just
lightly maintaining speed at a small throttle opening, like on a slight
downhill.  I took everything apart, and here's what I found.

Conditions Discovered:

* Rear driveshaft piece: one U-joint was old but OK, the other had one very
worn spider axis with the needles having dug their way into the journal and
taken a set in that orientation.  It didn't feel real bad before
disassembly, but looked bad once I got it apart.  Also on a couple journals,
the ends had worn pretty hard into the needle caps.  Guided by Glenn
Oliveria, I replaced both U-joints with OEM Alfa kits.  Also, the U-joints
were out of phase by one spline, so I reoriented the spline correctly.
According to a couple people, this should have caused big vibrations all the
time, but for some reason didn't.  The sliding spline was slightly worn, but
not more than normal. Kind of dry of grease. Rear section also had one old
dent in it, but I elected to put it back in as is.

* Front driveshaft piece: shaft bearing, rubber carrier, and front bushing
seemed fine. Donut is not new, but it seems OK.

* Trans yoke and ball: I'm glad I didn't assume the problem was just
U-joints, because the trans yoke on the output shaft turned out to be loose,
as in easily movable side to side by hand.  The nut was not even hand-tight,
though it had luckily bumped up against the lock plate.  I removed the nut,
replaced the rear seal, and put the yoke back on with a new lockplate and
locktite, and torqued it to 87 ft/lbs.  All that wobbling though seems to
have allowed the front driveshaft bushing to wear down the ball on the trans
shaft, from about .709" measured on two extra transes, to about .684" (.025"
wear) on this trans.  The wear is somewhat irregular.  I pondered my
approach to this problem a long time, finally deciding to just put it all
back together and see what the result was.  Changing the trans is a lot more
work.

* Differential yoke: having found the loose trans yoke and assuming it was
my problem, I wasn't inclined to check the diff yoke for tightness, but
Norman Racing assured me checking it with the castellated socket they loaned
me was worthwhile, so I did.  The nut had felt tight by a
screwdriver-and-hammer-tap check, but putting the right wrench on it allowed
me to turn it almost a quarter turn before it hit the torque wrench click at
87 ft/lbs.  Yikes.  I restaked the little soft lock parts on the nut (not
really useful, it seems, in preventing backing off).

Results:

Everything went back together without a problem in a couple hours. On
driving, the car has smoother take-off from rest than before, which I
viscerally attribute to the new U-joints.  The high-speed no-torque
vibration, the reasons for doing this in the first place, is now gone. I
think this must have been the loose trans yoke flailing around.  Conversely,
the car now has a slight whine in 5th gear that it didn't use to have.
Perhaps this is from the gear stack having been tightened up, now that the
trans yoke is tight and holding it all together properly.  I don't think the
diff. yoke was loose enough to cause problems.  It may be that I have
slightly more general rumble about 65 mph than before, but it could be that
I'm now more critical, because I'm looking for problems whereas before I
wasn't before.  Even though I marked everything and put it all back in the
same way, the shaft's overall orientation is now different, due to new
U-joints, different (correct) phase of the rear shaft, and tight front and
rear yokes. So my balance and straightness might be a bit off now. I'll
drive it awhile and see.  The only real fix for the worn ball is to rebuild
the trans with a new shaft, or replace the trans.  If I replace my trans,
I'll have the driveshaft checked for balance and straightness.

Moral:

Whenever you have a 101 through 115 driveshaft out, check the diff and trans
yokes for tightness if you don't know their history.  You can check the
front yoke without even removing the shaft by trying to pry it with a big
screwdriver or pry bar.  It should (obviously) turn around, but not wiggle
fore/aft or side to side.  One Alfa mechanic told me 1990-91 Spiders were
notorious for loose trans yokes right from the factory; the nut didn't
torque right for some reason.  Inspect and measure the ball and front
driveshaft bushing, and reassemble with plenty of grease and the rubber
cushioning/sealing piece.  Feel the U-joints, and make sure they are in
phase (lined up). Use only OEM Alfa U-joint kits.  Make sure the spline is
greased. Mark everything so you can put it all back in the same way.

Sorry to go on so long, but these driveshaft situations are never simple,
and the repair of this single particular problem revealed many things that
needed fixing, some potentially disastrous and dangerous.  Falling
driveshafts are bad.

Andrew Watry
Berlina Register
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