RE: GTV & Alfetta rear brakes

["John Fielding" <johnf@domain.elided>]

In AD V8 #688 Biba had this to say in reply to Brian Shorey's response to the problem.


Let me start with defining what I meant by 'over-engineering' the rear
brakes for these cars:

I doubt if one could over-engineer the cooling of the rear brakes.

However, my concern is one could over-engineer the 'stopping power' of
the rear brakes (whether hot or cold) and while solving the heat problem
one might well upset the front / back braking balance especially under
panic / very aggressive braking conditions.

Should I have gone through all of the 'basics' and was still having
problems, as mentioned before, I'd strongly consider installing some
sort of air ducting system to the rear calipers / discsor?

On page 77 of David Owen's 'Alfa Romeo Alfetta GT' book there is a photo
of a very nasty and aggressive Alfetta GT at the '75 Elba Rally (which
Alfa won). On it is a massive rear ducting system and one would assume
it is solely for the rear inboard brakes (although the transaxle might
also have benefited).

Dunno, but bet there is at least someone out there who has solved the
problem without resorting to 'out-board' rear brakes or perhaps even
vented discs in the rear.

Could well be wrong, but would assume they made the fronts work harder
so as to rely on / heat up the rears less and perhaps also used rear air
ducting.

Biba
Irwindale, CA USA

As far as overcooling the rears I think this is very possible.  Did you see how Formula 1
teams were taping up the front brake ducts during qualifying for the San Marino GP?  Brake
pads have an optimum working temperature range, too cold and they don't work, too hot and
they also don't.

Increasing the gripping power of the rear brakes IMHO is a wrong move, the setup & balance
of the car will be adversely effected during heavy braking making the tail more likely to
unstick and swing around causing a spin.  Ask me how I lnow that :(

The brake proportioning valve on the Alfetta,  I suspect it is the same as the GTV cars,
works by closing off the rear brake lines when the line pressure exceeds a certain amount.
Unlike my Fiat Uno Turbo where the brake proportioning valve actuator rod is connected
between the body and to the rear beam axle.  As the nose of the car dips under braking the
rear of the body rises and pulls the valve shut so preventing rear lockup, and it
automatically adjusts for extra load/passenger weight in the rear.  IMHO a better scheme
than the Alfa system.

As far as ducting air to the general area of the rear brakes and transaxle, I think that
too much air around the transaxle is unlikely due to the shape of the floorpan and under
floor airflow path.  A great deal more air will help the transaxle keeping the oil within
reasonable temperatures.

On my Alfetta race car I chopped two slots into the boot/trunk floorpan.  If you examine
the floorpan there are two rectangular depressions, one above each rear brake, I took an
anglegrinder and cut these out, but more for easy access to the adjusters and to make
changing pads simpler.  However since then the rears have behaved a lot better, maybe
psychological who knows?

My 02c worth.

John
Durban
South Africa
Alfetta 1.8L turbo
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