Re: Rear caliper rebuild

[Steve Manning <stephenm@ix.netcom.com>]

At 06:21 AM 6/10/98 -0600, you wrote:
>Hello all,
>
>I have a question regarding rebuilding rear calipers on a S4. My rear
>calipers have 62K miles on them and I will be pulling them off and
>disassembling them in an effort to get them powdercoated to match the big
>reds front. Vain, I know, but I am not in this to half ass it.
>
>I have rebuilt plenty of fixed calipers without parking brake functionality.
>I am assuming that the majority of the work on the rear floating caliper
>with the parking brake will be fairly straightforward. I already have the
>rebuild kit which consists of new piston seals, dust boots, and a special
>lubricant that the seals need to be soaked in for 45 minutes prior to
>installation.
>
>Do I need compressed air to get the piston out of the caliper? Or can I use
>the tool that is normally used to push (& turn) the piston back into the
>caliper body to pull it all the way out? Besides this is there anything in
>particular I should be watching out for?
>
>Thanks,
>Frank--

Frank - I've rebuilt one of the rear calipers on my '90 200tqw (upgraded
with V8/S4 calipers); it was pretty straightforward (except getting the
right rebuild kit, which was a pain - carefully check the sizes of the
piston seals & dust boots!)  I used compressed air to get the piston out.

The only thing that was difficult was the parking brake internals, which I
fixed because that was my main problem.  You may choose not to touch any of
those parts (and I never did find a picture or anything to help in the
Bentley).  The mechanism consists of a threaded rod (that the piston screws
on to) w/an o-ring, that moves the piston against the brake pads when it is
pushed by a 'cup' receiver that rotates when pulled by the parking brake
cables.  I know, not a good explanation, you have to see it.  There are two
keys to making this mechanism work:

1. The snap ring that holds the threaded rod to the piston body is intact &
in place.  Otherwise the rod will move, but not exert pressure on the
piston, and voila! no parking brake.  The snap ring is a b***h to get on;
there's no access for proper snap ring pliers.

2.  The o-ring that seals the threaded rod is working - it keeps the brake
fluid in the cylinder, and out of the external parking brake mechanism.
The end of the threaded rod that sits in the 'receiver' for the parking
brake lever must be lubricated.  My theory is that most frozen parking
brake problems happen because that o-ring leaks and corrodes the parking
brake lever.  Don't know if this is generally true, but I've seen it.

Hope this helps...........SLM

Steve Manning:  stephenm@ix.netcom.com
...Physical home: Metro D.C. area, USA
.....Virtual home:  http://www.stationwagon.com