[Amc-list] Re; Drilling brake drums.

["John Elle" <johnelle@xxxxxxxxx>]

I did a little web searching on this subject too and it comes back to me
as a mixed review. The technical answers seem to support that it is a
waste of time and money. 
On rotors, the cross drilling serves to vent the out gassing of hot pads
which if not controlled cause the pads to sort of hydraulic across the
rotors. However you only get brakes hot enough to cause the materials to
out gas in racing conditions. It is ( at least according to some web
sites) highly improbable that street rotors will get that hot. 
Drilling drums is argued that if you run through a flood, they will
drain quicker. Having had the experience my self on multiple cases,
water never had any problem getting in or out of drums. While they were
wet if you dragged the brakes a bit after leaving the flooded area, they
dried out rather quickly and would not cause a problem. 
As far as drum brakes failing due to heat, that was a typical failure
mode and I have experienced that too. It was always my understanding
that heat caused the drum to expand thus reaching a point where the
travel supplied by the wheel cylinder was exceeded so the wheel
cylinders capability of supplying pressure to the brake shoes was
greatly reduced. Even under the condition of over heated, they did not
get anywhere near the temperature of a disc brake assembly that was
working normally or even hard. Of course when the wheel cylinder of the
drum system tried to work under these conditions you would loose travel
with the brake pedal. 
I would be willing to bet that those who are actually reporting improved
operation of drum brakes when holes are drilled in the surface of the
drum are;
1. Trying to sell you the process of drilling holes. (Translated the
objective was to remove $ from the pocket.)
Or 
2. The brakes needed work anyway and when the effort was expended to
rebuild the brakes with quality materials they worked better than they
did before and it made no difference at all whether holes were drilled
or not.  A situation I find to be quite common in many areas.
 
Front brake design though is a significant factor in how the car stops.
For example the dual wheel cylinder system used in Chrysler cars on or
about the 1960's was quite iffy in the capability of stopping a speeding
Plymouth as compared to the dual servo system many other cars used at
the same time. But Buick around the same time interval had massive
finned drums on the front that had a reputation for doing and
outstanding job of woeing up those big heavy Electra 225s and is still
the front drum conversion of choice if building a street machine for
both looks and performance if you want to build something with drums. 
For what it is worth, that is what I come up with. 
Or you could use the cooling systems my Uncle used for his off road
logging trucks that clambered up and down the cut out temporary dirt
roads in the hills of Oregon. You mounted a 50 gallon water tank behind
the cab and dribbled water over the big huge drums they had then and
still do. About half way down the hill you would stop and refill the
water tank so you could have brakes for the rest of the trip. ;-)
John. 
 
 
 
 
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