Subject: UFO brakes on S4 1992

[C1J1Miller@aol.com]

Theo Malpassuti writes (to the quattro list):
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Hi all.
I am the current owner of an S4 1992, unlucky equipped with UFO brakes.
Is there any owners of 1992 S4 mounting the UFO?
regards, Theo
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UFO brakes are the unique internal caliper disc brakes developed by Audi for 
the '90-'91 V8, and the '91 200q (in the USA; used on earlier models 
overseas).  They are nicknamed UFO because of the appearance of the front 
brake rotor.  On UFO equipped cars, looking at the front wheels, you can see 
the metal basket that connects the rotor to the wheel hub.   See: 
http://www.digiweb.com/~wolffb/quattro/ufo.html

The concept was that by mounting the caliper assembly inboard instead of 
outboard, you could get more braking area with a larger diameter disc without 
increasing the size of the wheel.  Audi wanted to keep the unsprung mass low 
as well as increase the choices of tires available, and retain the larger 
sidewall on a 15 vs. 16 inch tire,
which increases comfort.  (There were more performance tires in the 15" size 
back in '88 or so when the system was developed).

A downside of this design is difficulty in finding aftermarket wheels that 
fit, especially without going to 16" or 17" wheels. Many of these cars 
suffered from warped front discs after just 20k miles.  However, many also 
had no problems...

Audi offered to replace the UFOs with regular 5000/200tq discs and calipers, 
and in some cases the G60 S4 disks and calipers, but only after a history of 
warped rotors on a car. This was to prevent expensive and frequent 
replacement of the front discs. 

The replacement involved replacing the entire front suspension.   The 
retrofitted cars do lose some braking power as the regular discs are only 
10.9 inches in diameter (about 17% less swept area than UFOs). 

Audi issued a technical service bulletin to dealers detailing the parts 
required to make this change... however, only cars under the original 
warrantee were allowed the "no cost" retrofit, and only after repeated 
problems.  The mounting system and possibly the discs were revised several 
times during production.  However, if you had issued a complaint (or several) 
during the warrantee period, and this was not resolved, you might have an 
argument for Audi to help pay to fix the problem.  If the issue is only that 
the brakes are worn out, don't expect anything.  I think cost for UFO system 
components are around $100 for a set of pads, and $375 per brake disc ($850 
plus labor for new front brakes, not including calipers, if needed).

The retrofitted braking system's disc swept area is about 17% smaller than 
the UFO system, and many who have completed the change feel they lost some 
braking power.  Advantages to the G60 system is the lower unsprung weight, 
and lower cost for brake work.  Additionally, most of the "brake upgrades" 
(larger calipers and rotors) require the G60 strut setup as well as minimum 
16" diameter wheels, with a notable exception being a bolt-on kit for UFO 
struts available through 2Bennett Brothers in California.  Sorry, no 
information on their kit; I have not heard from anyone who's used it.

A group of enthusiests are trying to make a more economical bolt-on kit for 
the UFO struts, but so far, it is not ready.  Stay tuned...

The technical service bulletin for the retrofit should be available through 
Audi, or on the Alldata CD-ROM (and referenced through their web site).  I 
believe the "retrofit kit" is no longer available through Audi, as they 
haven't been performing the change-overs for years.

If the symptoms you are seeing involve the steering wheel shaking under 
braking, you should have the front suspension mounts (bushings) inspected for 
wear, and replaced if needed.  The quattro list fix for warped front brake 
rotors is perform about 3 high speed sudden braking sessions in a row (to 
heat up the front rotors), then driving for a while to allow the brake rotors 
to cool evenly.  This often fixes the problems for a while.

I would also recommend pulling a front wheel, and removing the disc for 
inspection.  Several sets of UFOs that I've inspected have a rust issue where 
the inner and outer edge of the disc rusts, and the rust travels down towards 
the inside of the disc under the brake pads.  This leaves a nearly 1/2 inch 
inner and outer layer of polished rust, that can be chipped away rather 
easily, exposing the rust under the polished portion.  On the discs I've 
inspected, this surface is slighly raised, and wears the brake pads unevenly. 
 (This may be more prevalent with use of road salt in winter). This rusted 
area would lead to pulsating brakes, and reduced braking ability.

If you decide to switch over to the standard G60s used on the S4, I'd 
recommend getting a used set of front struts, as it will be much more 
economical.

Sorry for the length of the post, but this is a frequent question on the list 
(some one mentions UFOs, then 10 people ask what's a UFO, then....).  More on 
my site below, under repair, then brakes.
hth, chris miller, windham nh, c1j1miller@aol.com
'91 200q20v with UFOs, http://members.aol.com/c1j1miller/index.html