G60 brakes

[Phil Rose]

At 12:23 PM -0700 7/8/02, Bernie Benz wrote:
>  > From: Phil Rose <pjrose at frontiernet.net>
>>  Date: Mon, 8 Jul 2002 10:34:30 -0400
>>  To: Bernie Benz <b.m.benz at prodigy.net>
>>  Cc: 200q20V mailing list <200q20v at audifans.com>
>>  Subject: Re: G60 brakes
>>
>>  At 9:47 PM -0700 7/7/02, Bernie Benz wrote:
>>>  Phil,
>>>
>>>  If the externals of your G60s, the guide pins, were found to be
>>>in such poor
>>>  shape, do you assume that the internals are any better?
>>
>>  One guide pin out of four was in bad condition.
>IMO, impossible.  You must have an unrealistic defination of what
>constitutes a "bad condition".
>Examples:  A positively frozen guide pin(s), as you described, would cause
>the outboard pad to be ineffective, shifting all braking force and wear onto
>the inboard, piston loaded pad.  Contrast this to a stiff guide pins
>condition, in which the outboard pad would apply with high hyd. pressure but
>would not release, so would drag until it wears free.  This must be your
>stated second caliper condition, there is no other plausable rational for
>uneven pad wear which is excessive on the outboard pad.

No, Bernie, it's neither "impossible", implausible nor irrational--
if you'll (re-)read what I wrote.

The guide pins on the second (passenger side) caliper were not
"stiff" at all. This I can state unequivocally since their operation
was carefully checked when I removed and regreased them. What I
encountered (and described) was that the inner pad had become
"jammed"--i.e., stuck tight in the carrier and unable to be forced
against the rotor; and this apparently caused most of the braking
force to be applied via the outer pad. The inner pad's problem
resulted from corrosion and accumulations on the upper and lower
flats of the carrier, making the pad very difficult to remove--let
alone operate properly. Before a new pad could be inserted (let alone
slide freely), the upper and lower carrier bracket surfaces required
considerable scraping and cleaning. Oh and FWIW, there was no problem
retracting any of the pistons (using hand pressure) for the new pads.

In the first caliper, the pad wear happens to have been quite even
(inner vs outer), which suggests that the guide pin freeze-up may
have been a fairly recent ocurrance. You, living in Nevada, may not
realize--or possibly have forgotten--how quickly corrosion can occur
in the salt belt; although I don't for a minute believe that these
brakes had rigorous maintenance. On that we agree.


>
>A fluid flush is at best a preventative against further, future
>deterioration of the hydraulic system.  It can not correct existing
>problems, such as frozen, sludged up, or not retracting pistons.
>IMO,
>having a "new" 11 year old car without hard service history, one must assume
>the worst, that the fluid has never been changed and that the hyd system is
>all sludged up and pistons are not retracting properly.

See above--I believe there's no evidence to support your grim,
long-distance diagnosis.
While I can't assert the front brakes are yet at 100% (or that they
wouldn't benefit from a full rebuild in the not-distant future), I
beleve thay are of providing a reasonable margin of safety right now.

>   Please, do a full
>bore hydraulic overhaul, all 4 calipers, before letting your wife "drive it
>around town".

At least _we_ won't be driving with paper-thin rotors and pads. ;-)

I do appreciate your advice and concern.

Phil
--

Phil Rose
Rochester, NY
mailto:pjrose at frontiernet.net