Cobra surge brakes on mountain grades.

My new (to me) Ventus C came with a decidedly old Cobra trailer. When
I pulled the wheel drums (one was cracked) the surfaces resembled a
dirt road after the spring run-off. I replaced drums and brake shoes
and was back in business. My first towing adventure included the long
downgrade into Calestoga at the end of which I stopped for gas, and
casually rested my hand on a Cobra wheel hub in an experimental sort
of way. EEEyooouuuugh! I barely avoided second-degree burns.

Why had this happened, I wondered? I drive a stick shift Volvo and had
followed my usual practice of engine braking with intermittent use of
the car's brakes. A little thinking convinced me that the Cobra didn't
know this. Once the surge brakes were applied, they stayed on so long
as no acceleration was applied to the Volvo. The message of the wheel
hub was that the surge brakes had been engaged all the way down that
grade.

Fortunately, another mountain lay ahead of me, and after towing to the
top of Mt. St. Helena, I applied a new technique to the down grade -
tapping the accelerator briefly after each application of the brakes
so that I could feel the surge piston disengaging. Sure enough, when I
stopped at the bottom for a (very cautious) testing of the wheel hubs,
they were only mildly warm.

Most of us know enough to tie down the Cobra's hand brake, which has a
nasty habit of springing shut during a bumpy tow, but I've never heard
anything about handling surge brakes on mountain grades. Is this new
lore, or have I misses something that everybody knows?

Matt Herron