Re: [CBQ] 1960s red+black MU diesel lashups

["Winton" <runextra@gmail.com>]

Keep in mind that locomotives GP/SD9 and earlier had different dynamic brake 
systems and different multiple unit air brake systems than those on GP20s and 
later models.  In other words the two groups would not fully multiple unit with 
each other. Early units used a Field Current Loop dynamic brake control while 
later units used a Potential (voltage) Control system. The Field loop control 
needed a second MU socket on the locos for the 3 wire Field Current.  The early 
MU air brake system used a brake cylinder pressure equalizing hose that the 
newer units do not have. The newer units use an Application & Release MU hose 
(similar to the older Cylinder Equalizing hose but not quite the same thing) 
plus an Actuating hose instead. So you have two things that caused problems 
when trying to MU the older units with the newer units.  Now having said all 
that, some CB&Q GP30/35 (dont recall if I ever had any GP40s this way) had both 
sets of MU air hoses and had the earlier field loop Dynamic Brake sockets. They 
had electrical switches on the back cab wall that could be set when building 
loco consists to select the proper needed DB control system.  But the loco 
consists had to be built in specific unit order for all this to work. The 
relatively few early 2nd Generation CB&Q units are the only units I saw during 
my career that had that dual Air Brake & Dynamic Brake control system 
capability and I had a lot of foreign unit power back in the day. However, of 
course none of the above prevented Chinese Red GP/SD9s to be mixed with 
Blackbird GP/SD9s. 


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