Re: Brake booster diagnostic?

[Scott Fisher <sfisher71@domain.elided>]

Following up to this one for thread-sensitive archival
purposes.

Thanks to Joe Cantrell, Tony Sims, Will Owen and
several others for offering insights into the
diagnosis of vacuum-assisted brakes.  The results are
quite encouraging so far, but I wanted to follow up to
the digest at large to help others, including Mitch
Wolberg who's getting close to wrecking a perfectly
good parts car over the brakes. :-)

My symptoms were much like what Mitch describes: long
pedal travel, very soft feel.  I bled the system once
shortly after acquiring the car and it was *better*
but still not great.

On the AROO tour in May, the Berlina's brakes went
from having a long soft pedal to having a long soft
pedal with about half the braking action of my Spider.
 Scary.  So I put it up and set aside some time to
diagnose it.

Several people asked me if it was a booster problem,
and I realized I had no idea how to check, so I asked
the digest and got some good responses.

Here's how to see whether your booster is working
correctly:

With the motor off, pump the pedal a few times to use
up any remaining vacuum in the system.  Then press the
pedal down and hold it while you start the car.  If
the pedal drops down once you start the car, the
vacuum system is working.

A second set of tests (from auslander, er, stranieri
automobili): turn the car off, then pump the brake
pedal gently a few times.  The pedal should come up
higher each time for three or four pumps, then stay at
the higher setting.  This is because you're using up a
little more vacuum each time you pump the pedal.

My Berlina passed both of those tests easily, so on
Joe Cantrell's recommendation, I replaced the front
pads (his reasoning: pads, then rotors, have the
greatest effect on pedal position).  Why the fronts? 
That's all I had in the parts box, new Axxis Deluxe. 
(A set of new rear pads is on its way.)

Before continuing, a side comment: BOY, is it a breeze
to replace 115-series Alfa brake pads.  You need the
right-sized punch (thin, without much taper) to knock
the pins out of the calipers, but after that it's
incredibly easy -- remove the spring clip, slide the
pads out, lever back the pistons, insert the pads,
insert the spring clip, put in one pin, then bend the
spring clip and put in the other pin.

What I found on my Berlina: about 2mm of friction
material on the pads (that is, the "rivets" weren't
showing yet), but the worst glazing I've ever seen on
pads.  The rotors also looked as though they hadn't
had a lot of friction, and I'd just been driving the
car (took my son to lunch).  Both pads and rotors
looked polished and waxy; were they shinier than the
paint?  Could be... 

The left-outer piston was slightly stuck, in that I
had to use more force on it (significantly more) to
get it to retract than I did on the other three, which
moved fairly easily.  Tip: slide the old brake pad
back in as a spacer, you'll get better leverage with
your pry bar.

A word on brake pad replacement: the first time you
press on the pedal after replacing pads, the pedal
WILL go all the way to the floor -- something about
displacing the fluid in the calipers.  Two or three
quick pumps bring it back, but be sure to do this
BEFORE you try to drive the car.

Once the new pads were in place, I took the Berlina
out for a short (but slow) test drive.  There *was* a
slight improvement in brake feel... and a slightly
more noticeable one in effectiveness.  Then I
remembered about bedding in the pads.

Often, when I have replaced brake pads, the new ones
were marginally worse than the old ones on their first
drive around the block -- I remember, more than once,
wondering why I'd gone to the trouble when I only made
the brakes WORSE.  Of course, once the pads bed in,
they work a LOT better.

That's my experience so far: by the time I got back to
the driveway, the brakes were feeling decent, and by
the time I got back from picking up takeout Chinese
food for Saturday dinner, they were about 80% as good
as the Spider's brakes -- but STILL with a soft pedal
with a lot of travel.  I'll hold off on doing any more
bedding-in, and wait for the new rear pads to arrive;
I've got about 3, maybe 4 miles on the fronts.

One other comment: a couple of Berlina owners
suggested plugging the vacuum assist line at the
intake manifold, because they felt the brakes were
overboosted in stock form and preferred the feel of
the unassisted brakes.  Others have commented that
Berlinas seem to have softer-feeling brakes than other
Alfas; considering that the brakes in my Spider felt
soft to the point of weakness when I first drove it,
this could be a design decision on the part of Alfa's
engineers.  I would be very interested in hearing from
people who owned new Berlinas -- did they always have
this soft brake pedal?  (If the new brake pads are any
indication, there's certainly nothing wrong with the
way they work.)

--Scott Fisher
  Tualatin, Oregon
.
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