A new form of e-brake failure

[Paul Heneghan]

Hello everyone,

I've got a new type of handbrake problem (car is a 1984 Audi 80 quattro -
similar to a 4KSQ, rear brakes also similar to Audi 100 or 5K) which I've
never seen before and which doesn't appear to be documented in the archives.

I'm familiar with all the usual forms of problems, usually resulting in no
handbrake operation at the caliper:
seized handbrake cables
rusted parking brake mechanism operating shafts
rusted threaded shaft piston

I've even plagiarised the works of others, added my own caliper rebuild
experiences and published a fairly lengthy web page on this topic at
http://heneghan.members.beeb.net/audi/parkingbrake.html

The new problem is a self-adjusting mechanism that apparently allows the
piston to retract when the handbrake is put on.  The handbrake mech. should
press on a lozenge-shaped rod (about 15mm long) which in turn should press
on a small piston at the end of the very large threaded shaft.  This screws
into the piston which pushes the pads together.  There is a self-adjusting
mech. in the piston which allows it to very slowly unscrew itself (the
external part of the piston doesn't need to rotate, only the internal part)
outwards to compensate for pad wear.  In my faulty caliper, it is possible
to press on the piston and push it back into the caliper without needing to
rotate it which implies a collapsing or reversing self-adjusting mechanism.
This cannot be right, can it?

Any help gratefully received.

Paul



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