The trucks under SD40/45s were a revised design different from those
used on SD7/9s. The original SD40/45 trucks (1966) had four large
(about 11 inches) brake cylinders mounted under the truck frame between
the wheels. These brake systems were single shoe per wheel and used
composition brake shoes, among the first such applications on
locomotives Earlier SDs used traditional clasp brakes with two cast
iron shoes per wheel and six brake cylinders. Independent brake
cylinder pressure was raised from 45 psi to 72 on the single shoe
application. The braking characteristics of composition shoes are
considerably different from cast iron shoes. Crews had difficulty
getting used to them. They didn't brake as well, particularly at slow
speeds. The original underslung mounting arrangement was troublesome
and relatively high maintenance. In addition, there was a problem with
the hand brake. It could be set against the air in the brake cylinder
which if it bled off would allow the hand brake to release.
By the time that the Q ordered their SD45's in 1968, these negative
conditions were rather well known. The Q and a few other RRs, (notably
Norfolk and Western) specified a traditional clasp brake cast iron shoe
arrangement on their locomotives. NP and GN both had very early SD45s
and continued to ordered the original arrangement, which, by 1969, was
modified. The first modification was three cylinders low and one high
at one corner of the truck. The hand brake was connected to the lever
of the high cylinder, eliminating the bleed off problem. As further
problems occurred with the low slung cylinders, all four were
eventually raised to the high corner positions. In 1972, the truck was
totally superseded with the high adhesion Dash 2 truck. These were also
available with single shoe or the clasp brake arrangement, but all
brake cylinders were always high mounted.
As for the photos of Unit No. 527 on p.33 and 114 of Mike Spoor's Vol.
#2, (also on p.111), you had better look again, There are definitely
three brake cylinders on the side of each truck, just the way the units
was built. The photo on p.114 is particularly clear. The center
cylinder is a immediately below the jacking pad on the locomotive frame
at each truck.
Bill Barber
On Saturday, January 11, 2003, at 07:35 AM, BRHSlist@yahoogroups.com
wrote:
There is 1 message in this issue.
Topics in this digest:
1. SD-45 trucks
From: "Jerry Krueger <jakrueg@n...>"
<jakrueg@n...>
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Message: 1
Date: Sat, 11 Jan 2003 12:03:27 -0000
From: "Jerry Krueger <jakrueg@n...>" <jakrueg@n...>
Subject: SD-45 trucks
There's been recent talk about both Kato and Proto2000 issuing SD-45
models on HO. It's got me thinking about doing a Q unit in premerger
green and black. After going there some books and some online
research, all the pictures show the SD-45s with 3 brake cylinders on
there trucks. Pictures of ther roads sd-45s show the typical 2 brake
cylinder trucks. See pictures in Mike Spoor's Vol 2, page 33 and
page 114.
I believe the Q was one of the first roads to purchase the Sd-45s
from EMD, did EMD originally use trucks from SD-9s or SD-24s and then
switch to a 2 brake cylinder design? Where these trucks from traded
in units? From a modeling standpoint, could I use the
trucks/sideframes from a SD-9 or SD-24, are the axle spacings the
same. All the reference material I have (drawings in mags) show the
2 brake cylinder design.
Any help is appreciated.
Jerry Krueger
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