There was recently a thread which speculated on why Santa Fe bought 4-unit F3's and 3-unit Alco-GE and Fairbanks-Morse diesels for passenger service after World War II, and thereafter kept the fleet of E-units east of La Junta. One reason was that 6,000 horsepower locomotives other than E-units could pull a passenger train on the 3.2% grades without a helper engine. That one is obvious. The reason the E-units were not suitable, even if m-ued into 6,000 horsepower consists, is that they had such comparatively high continuous speed requirements that they would have been in the short time ratings for the traction motors every trip, unless they had a helper.
As speed diminishes on an ascending grade, the traction motor amperage increases, producing more heat in the traction motors. Traction motors don't have winding, like open-frame Lionel postwar motors. Instead they have copper commutator bars "cemented" radially around the center with "plastic" filling the spaces between commutator bars. If excessive heat develops, expansion of the commutator bars may loosen the "plastic's" ability to hold tightly, and centrifugal force can pull the commutator bars outward, with resulting destruction.
I used my 1952 ATSF Operating Manual for Diesel Locomotives to get the following figures, which demonstrate the reasoning behind the decision to keep the E-units on the plains and off the mountains.
CLASS BUILDER MODEL MINIMUM CONTINUOUS SPEED (MPH)
50 Alco-GE DL-109 34 (2-units, 4,000-hp)
80 EMD E8m 31 (2,000-hp - used generators/traction motors from E1's)
11 EMC E3/E6 28 2 units, 4,000-hp)
51/52 Alco-GE PA-1 23 (3 units, 6,000-hp)
90 FM/GE Erie-Blt. 23 (3 units, 6,000-hp)
16 EMD F3 22.5 (4 units, 6,000-hp)
37 EMD F7 18 (4 units, 6,000-hp)
300 EMD F7 18 (4,500-hp bobtails)
100 EMC FT 14.5 (65 MPH blue freight units sometimes used w/boiler car)
325 EMD F7 14.2 (80 MPH rednose dual-service 4,500-hp bobtail units)
200 EMD F7 11 (65 MPH blue freight units, some of which had steam generators)
Unless otherwise noted, the gear ratio was good for somewhere above 100 MPH, which was the maximum authorized speed for Santa Fe passenger trains until around 1960, when it was lowered to 90. My manual was issued just after the last 4 rednose FT's had been regard back to 65 MPH. When the rednose FT's were geared for 100+ MPH, their minimum continuous speed would have been somewhere in the mid-20's.
There was an additional reason for keeping the E-units on the plains. If you go up one side of a mountain, you have to go down the other side. Santa Fe pioneered the use of dynamic braking on passenger trains, and insisted that Engineers use it, to reduce the cost of brake shoe and wheel wear, as well as to avoid unnecessary heating of wheels, which allowed higher speed on descending grades. The E3, E6, E8m units, as well as poor old DL-109 50, did not have dynamic braking.
The E1A units remained on San Diegan and Golden Gate trains in California, until they were traded back to EMD in 1952-53 on the E8m's which recycled the GE electrical equipment and therefore were not comparable to true E8's. The E8m's worked these assignments for about a year after delivery. When there were enough F7's available, Santa Fe just put a couple of bobtail F7's to work on the Golden Gates and rotated overland units to San Diego during layovers at Los Angeles, and the E8m's joined the other E-units east of the Rockies. The Denver trains did use E8m's, but were only 3 or 4 cars long, and did not lug down below 31 MPH on the ascending grade. The San Diegans did have to climb a 2.2% grade from Sorrento to Linda Vista but it only took 10 minutes and did not put the E8m's into the short time rating.
I hope this helps forumites understand the reasoning behind Santa Fe's business decision to use the E-units on flat or undulating territory, where they could give excellent service, and to replace them with locomotives that could handle mountain territory at less cost.
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