[urq] G60 problem

[Eric Renneisen]

If you looked very closely at the pictures of my '86 on the way back
from Vancouver, you might have noticed that the left front wheel seemed
exceptionally dusty.  I suspected that the caliper was sticking, even
though the PO told me they were factory new G60s.  I am also still
getting some front end vibes, despite the PO replacing the A-arm
bushings.  I decided to investigate today.  As I tried to pull the
caliper off, I could tell something was wrong.  It took quite a bit of
effort to get it free.  Here's what I found:

http://home.comcast.net/~eric.renneisen/left3.JPG

Notice how one piston is corroded inside and the other is relatively
clean.  The clean one was the sticking.  When the brake pedal was
released, the smaller piston would retract, which would allow water
inside, and therefore more corrosion.

After some wrestling, I got the problem piston out.  Here it is:

http://home.comcast.net/~eric.renneisen/piston1.JPG
http://home.comcast.net/~eric.renneisen/piston2.JPG
http://home.comcast.net/~eric.renneisen/piston3.JPG
http://home.comcast.net/~eric.renneisen/piston5.JPG
http://home.comcast.net/~eric.renneisen/piston6.JPG

Definitely a problem.  The corrosion is more than can be polished away.
The caliper looks OK inside except that the lip between the dust boot
and the piston seal is heavily corroded.  Even with the seal removed,
the clean section of the piston is reluctant to move against that lip.
It can probably be cleaned up, though.

What's weird is that the dust boot seemed intact.  Somehow, moisture got
in between the boot and the seal and ate away at the piston and the
outer lip of the bore.  I'm convinced that this is the cause of the
front end vibrations (either directly, or the seized piston caused the
rotor to warp).

Hopefully a new piston isn't too expensive.  Any advice on the corrosion
between the dust boot and the seal?  Can I just clean that up with a
dremel?

Eric Renneisen
'94 S4
'90 CQ
'86 urq
'85 urq
Chattanooga, TN