[200q20v] RE: [s-cars] Big Reds (actually Blacks)

Michael (Prospeed Motorsports) michael at prospeedmktggrp.com
Tue Nov 6 08:45:35 EST 2001

I really don't want to start a pis_ing match here... But this is very
incorrect. While it is correct both calipers use the same mounting
configuration and they use different sized rotors... Everything else is
completely incorrect. The two pads have DIFFERENT SIZED backing plates.
In fact the backing plates don't even look the same. I have both in
stock and will post photos later to illustrate. If you install a 993
(S4) pad into a Big Red, it will not be held securely and will flop
around. A Big Red pad is too tall for a S4 caliper. Again I will post
photos later to illustrate.

And FWIW, if you were to attempt to use an S4 caliper with a 993tt rotor
the theoretical mounting height difference would be 9 mm not 4-5 mm. And
even if you made up for this difference in the mounting adapter, you may
run into radius issues in the caliper. The S4 caliper has a radius for a
304 mm diameter rotor and the 993tt caliper has a radius for a 322 mm
diameter rotor. I just checked the two calipers and rotors and it
appears there would be a clearance issue with the smaller caliper on the
larger rotor.

My other .02 here is, no offense meant to Scott, but these rotors and
calipers were designed to work as a system, with specific components
matched to work with other specific components. Not using the pieces in
the correct manner with the correct parts can lead to system failure. I
recall going through this a year or so ago on this list to the point
that I gave up and left the list completely. For instance, as I recall,
and I may be slightly off on my recollection, but BIRA was doing a kit
that used a Porsche caliper designed for a 32 mm thick rotor with an A8
rotor that, as I recall started as a 30 mm thick rotor. The significance
of this is Porsche and Brembo clearly state the wear limit on the rotor
is 2 mm. Meaning when the rotor is down to 30 mm thick it is done...
Throw it out and get a new one! Why? Because that is the design limit of
the caliper. If you run a 30 mm rotor done to 28 mm and you have half
wore pads, you run a SERIOUS risk of first ripping the dust seal,
allowing crap to get into the piston bore(s) ultimately destroying the
caliper from a scratched bore that will no longer seal, and/or the
caliper piston hyper extending and breaking the inner pressure seal.
This would cause a failure in brake hydraulic system.

I know... I know... There are many folks out there that are running
these (and other) setups that are perfect in design. I can only
ask..."Is the risk worth it to you?

BTW, as I don't sell adapters for any Audis, I have no vested interest
in this conversation other than I hate to see incorrect info being

I will post the photos later to illustrate my earlier points.

Michael G. Wachholz
Prospeed Motorsports

952.249.1169 office
952.475.3267 fax

400 Pond Ridge Circle
Wayzata, MN 55391

mailto:michael at prospeedmktggrp.com

> -----Original Message-----
> From: qshipq at aol.com [mailto:qshipq at aol.com]
> Sent: Tuesday, November 06, 2001 8:06 AM
> To: michael at prospeedmktggrp.com; adm1txs at ups.com;
> KBATTPO at yahoo.com; t44tq at mindspring.com; s-car-list at yahoogroups.com
> Subject: Re: [s-cars] Big Reds (actually Blacks)
> Both are right IME/O.  Tom probably more.  The difference in
> the 993 vs the 993tt is the rotor size vs the caliper mounting tabs as
> points out.  That said, Michael is right that the pad is smaller on
the non tt
> version.  However, both pads use the same backing plate, and drop into

> either caliper. The difference is really the rotor application, NOT
> caliper application. All that's required of the 993 caliper to replace
a tt
> caliper is 4 5ml mod washers and 4 993tt pads, btdt.
> You must also be careful to make sure that you order the tt
> pad if that was what you designed your application for.  A local
> screwed up and ordered the smaller pads for one of my customers (hence
> know it "drops in"), which resulted in a huge ridge on the larger
> and bucking of the top of the pad against that ridge.
> Igor, if you are making your own brackets, any machinist can
> add or subtract the 5ml from the caliper mounting dimension.
> Scott Justusson
> 993tt calipers and pads '87 44tq
> Tom Saltino writes:
> The 993 and 993tt calipers are very much the same calipers. 
> The turbo pads drop right into the non-turbo caliper.  the
> difference is in the small "ears" where they mount to the
> car.  The turbo calipers are about 5-6mm are taller to
> accommodate the larger diameter rotor.  You could have
> someone fab a bracket that will compensate for the difference
> and still use the larger turbo rotor w/ the non-turbo caliper.
> Tom
> MW writes:
> The 993 & 993tt calipers are NOT the same. They even use
> different pads. The tt pad is approximately 12.5 mm taller
> (just measured them as I have both here) They have different
> part numbers although the mounting is the same. On Porsches
> you use the exact same adapter to fit the S4 caliper (what
> you are referring to as the 993 caliper, first was seen on
> the 87 928 S4) as for the Big Red (993tt caliper) which was
> actually first seen not on a 911 but on the 93 928 GTS.
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