UFO brakes "warping"

[Joseph Yakubik <75363.2524@compuserve.com>]

Being the owner of a US spec '91 200qw with the UFO brakes and having read some
of the "It's gonna happen, they're crap..." and "No, I quite like mine..."
posts; I'll throw out my opinion.

After driving my car in Europe for about a year I started to experience a shimmy
from the front end.  This was at the 50k mark on the car, and I assume the
original rotors and pads.  Not wanting to subsidize the dealer for work that is
really, really easy. (Pad change UFOs is simpler than normal calipers). I did it
myself.

First:  buy the rotors as an exchange part.  They have the same part number,
just with an "X" on the end.  This knocks off over 40% of the price.  Don't
expect to see the part listed as an exchange on the 200 fiche.  Tell the dealer
to look at the V8 fiche.

Buying the pads may or may not be a dealer only option.  I haven't found them
anywhere else, but I've heard there are suppliers.  Keep the backing plates,
there are one or two listers out there trying to have carbon pads made up and
can use these.

Install is simple, follow the Bentley, use the Sears $9.95 piston compressor
tool.  Both sides: rotors, pads, sensors = 45 min, max.

The sensors work on a continuity principle.  If either side loses continuity the
alarm goes off.  The system is serial, and goes through the left side first.
Unplug this connector, check one side for power, the other for continuity to
ground.  If both sides are okay it could be the sensor you just pulled.

Care and feeding:  as has been posted the past few days, cooling is important.
I don't have any trouble keeping the ducts open and clear, but I don't use my
car as a snowplow or U-boat.  I have driven in the ice storms across the lower
mid/southwest.  It's tough to avoid crud build-up. 

My personal opinion on the "warping" is that it doesn't warp.  When I removed
the old discs I had "imprints" or "shadows" from the old pads in the discs.  I
think that if the rotors get too hot and you leave the pads in contact too long
some pad material "bonds" to the rotors.  Your brakes will then grab or feel
like a shimmy when the pads come in contact with the "bonded" section.  This
also jives with the "don't park or stand on the brake with hot brakes" and "a
few 80 mph to zero stops make the warping go away".

How to fix this problem:  dunno, better rotors (cooling, less porous alloy?) or
better pads (higher temps?).

Reference point:  Mine started "shimmying" at about the same time my pad warning
went off.  I seated the pads, but not as aggressively as I had on my old Jetta.
No wobbles, shimmys, grabs, etc in the last 20k miles.

Joe Yakubik