> As I recall, an SD45 only had one step of transition, while the SD7s and 9s
> had three. Early SD45s also had shunting steps
Yeh, the early SD45s had 6 different shunt conditions in series-parallel and 4
steps of shunt in parallel! Parallel shunts could go to the same 6 steps as
series-parallel _IF_ the engineer was brave enough :-)
Now count both forward transition & shunt steps plus reverse transition and
shunt steps and that is a lot of detecting and relays clacking!
Around the Sheridan/Gillette, WY area in the 1970-1980s low speed loading of
coal trains before computers required locos equipped to lead and trail a
"Pacesetter" box. This was a separate easily removable metal box maybe 9x9x5
inches that mounted on top of the control stand and had 2 screw-on cables that
connected to the back of it. Flipping a switch on the lead loco to Pacesetter
Operation caused the main generators/alternators fields on all units to respond
to a varying voltage control signal on an "optional" MU cable wire. That signal
was supplied by the Pacesetter box and it varied according to loco speed. The
Pacesetter could control speed to within less than 1/10th of a MPH. Loading
coal at 0.25mph was not unusual. The pacesetter had various knobs to set the
speed and a meter to show the loco was operating at the set speed.
Some times you'd get a unit that was not equipped for pacesetter operation.
These units would continue to load normally and had to be isolated while
loading coal. MILW units and others were like that. If it was the lead unit
then you had to go back to a pacesetter equipped trailing unit and load coal
from there.
One night I got an officer special out of Billings, MT to Sheridan. It had a
new SD40-2 and a new GE C30-7 for power. The first car of the train was a power
car for lights & heat. The carmen plugged in the MU cable between the 2nd loco
and the power car. Unbeknownst to anyone on the train crew or the RFE that act
set up the GE to trail a pacesetter. Apparently a conficting use of the same
"optional" MU wire. After departure I soon realized I only had one loco
operating. I could not maintain the Train Order schedule with the 18 car
passenger train. So when we arrived at Sheridan 2 helper units were added to
the point for the trip to Gillette. The problem was finally figured out at
Alliance or Lincoln. The MU wire that set up trailing units for Pacesetter
operation was apparently the same wire that was used on passenger locos to
control the steam generators on trailing units. Those locos had toggle switches
and lights in front of the fireman's seat for that purpose. So when the carmen
had plugged in the MU cable between the freight units and the heater car the
heater car screwed things up on the trailing GE.
So you see, even in modern times there are occasionally problems with
incompatible MU wiring.
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