SP5103 Wrote:
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> Most, not all, were built as A-1-A type
> flexicoils. This gave them the same axle loading
> as a 80-85 ton locomotive or car. Many of those
> Canadian branches had light rail but it wasn't
> politically possible to abandon them or always
> financially feasible to upgrade them.
>
> The disadvantage to an A-1-A freight design, is
> that only 2/3 of the locomotive weight is
> available for adhesion. Compared to a comparable
> SW1200, they only had 2/3 of the starting tractive
> effort, but their low hp (1200) meant their
> continuous tractive effort was likely right around
> the nominal minimum 25% adhesion.
>
> As the light rail branches were
> sold/abandoned/upgraded, there was no longer an
> operational advantage to having a fleet of
> locomotives with light axle loading. CN had
> several rebuild programs which resulted in many of
> them being rebuilt with salvaged B-B flexicoils.
> The basic electrical circuit required no changes
> as it was already four-motor.
>
> Similar situation existed elsewhere. Pacific Great
> Eastern (BCR) bought Alco RSC2/3 units, retrucked
> them to B-B as track improved. Milwaukee had some
> Alco RSC3 and SW1s with mu to run some of their
> prairie branches. SP's first big Baldwins were
> 5200-5202 DRS-6-4-1500 (A-1-A) and two were on the
> Toledo branch until it was upgraded, then ran out
> of southern Arizona until two sold with the
> Nacozari line and third was scrapped. SP also had
> a a few 44 tons and large fleet of 70 tons (as did
> CN) whose use declined as light rail/bridge lines
> were sold/abandoned/upgraded. SP still had
> SW1-SW8-SW900 units until they were no longer
> needed. There were still a few places the SW1500s
> ran in deference to lighter rail, as well as the
> first order of SD9s (scattered in low 4300s when
> rebuilt) that were lighter (as were the early C-C
> Baldwins).
>
> The reason that the GMD1s survived so long is that
> there was still a use for them, either on light
> rail as A-1-A or where a low hp road unit works
> just fine. Compare that to UP who sends out
> numerous locals with a pair of GP60 or SD40/60
> units where one smaller reliable bidirectional
> unit would work fine.


Wow dude! Thanks for the killer reply.