“Did the MCB or later the AAR mandate how much brake effort a car should have, presumably based on loaded weight?”
As recommended by the AAR’s Brake and Brake Equipment Committee the Arbitration Committee added the following to Interchange Rule 3 in June of 1937.
Rule 3, Section (b), Paragraph (9). Braking Power: On and after January 1, 1938, all freight cars offered in interchange having single capacity brakes shall have a nominal braking ratio
of not less than 60% nor more than 75% of the empty car weight, based on a brake cylinder pressure of 50 lbs. per square inch, except refrigerator cars weighing 53,000 lbs. or more, which shall have a nominal braking ratio of not less than 50 nor more than
60 percent of the empty car weight, based on 50 lbs. per square inch brake cylinder pressure. In Interchange.
The date of compliance was extended (annually) and minor revisions were made to the rule until the final compliance date of January 1, 1956 as announced in 1955 Supplement No. 1.
The 1956 Rule 3, Section (b), Paragraph (9):
All freight cars offered in interchange having single capacity brakes shall have a nominal braking ratio of not less than 50% nor more than 75% of the empty car weight, based on a brake
cylinder pressure of 50 lbs. per square inch, except refrigerator cars that are not equipped with one-wear or multiple-wear wrought steel wheels, which shall have a nominal braking ratio of not less than 50 nor more than 60 percent of the empty car weight,
based on 50 lbs. per square inch brake cylinder pressure. In Interchange.
Guy Wilber
Reno, Nevada
