307 and 410 at Santa Ana Junction
Jack Finn Collection
A two-car train headed by Pacific Electric no. 307 and trailing Metropolitan Coach Lines no. 410 rattles its way across the tracks at Santa Ana Junction headed south for Lynnwood and Bellflower.
Jack Finn Collection
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Can anyone comment on the possible performance difficulties caused by two mismatched cars – the 307 and 410? The 307 was a so-called hot rod with a higher speed gearing than the ex-IERR 410 as well as higher hp motors. I recall reading in an old Interurbans issue that the 300’s had a top speed of 55 mph whereas the IERR cars were only capable of 45 mph. Can someone educate me further on this?
Essentially each car does what it can, and there isn’t a problem. A car with a low numerical ratio of ring gear to pinion, (capable of higher speed) will not accelerate as fast as as a car with a higher numerical ratio, which doesn’t have as high a top speed. The issue of traction motor overspeed (not car overspeed) is almost non-existant among MOST of the later cars. These two cars would accelerate slightly faster than the slow one, and would go slightly faster than the slow one by itself, but not as fast as the faster one by itself. Think of a trailer with one or two powered cars, the whole group just accelerates slower, and has less top speed. A traction motor will produce its most torque at low speed with full field current, and its highest speed with a good part of the field shunted out.
Traction motor gearing and horsepower differential was a real problem with diesel-electric freight locomotives in the early 50s coupled to later locomotives. A higher speed freight locomotive, or passenger locomotive, has a higher minimum speed, the speed where the traction motor current drops below the maximum continuous allowable at full throttle. When this locomotive is run with a lower speed unit, with the lower speed unit leading, the lower speed unit’s loadmeter will be out of the red zone, while the faster geared one trailing will still be in the red zone if somebody went back to look. Overheated traction motors would result if something wasn’t done to either reduce the tonnage, or obtain more power.