Diesel "C" truck sideframes

The term "C" truck refers to a 3 axle truck where all axles are powered. Typically these trucks are found on switcher and road-switcher trucks, because the 3rd axle allows the load of the locomotive to be spread over more axles, and, for modern trucks, allows additional adhesion. Modern in this case is probably after about 1960.

The models and variants

Alco double-equalized trimount truck

Several versions of this truck, with a 12 foot, 6 inch wheelbase, were produced by Alco. The early version, found on the PRR RSD-5, featured a large brake cylinder mounted between the pair of axles with a larger space; A later version, found on the Pennsy's RSD-12s, C-628s and C-630s, had 2 brake cylinders mounted at the outsides of the truck. The shape of the equalizers also varied, sometimes have a straight lower edge, sometimes sloping up toward the center of the truck. These were very similar to the truck found under early GE 6 axle units.
Atlas/Roco RSD4

Commonwealth cast trucks

One well-used design was a Commonwealth-style, cast, straight-equalized truck made by GSC. It has a 13 foot wheelbase, and featured plain bearing journals. Baldwin, Lima, and F-M all used this design, which rode poorly on rough track. It was, however, not designed for high speed operation. Some of the Baldwin AS-616s, some of the RT-624s, and all of the Lima centercab transfer units of the Pennsy were equipped with these trucks. Stewart made the only known model of this truck.

Baldwin double-equalized trimount truck

Later Baldwin models using C trucks were equipped with a double-equalized, roller-bearing truck, also made by GSC. It was similar to the Alco double-equalized design, but used more springs and deeper equalizers. The wheelbase is unknown to me. Some later Baldwin units, including late-production AS-616s and RT-624s of the Pennsy. There are no known models of this truck.

GE double-equalized trimount truck

Early General Electric 6 axles models used another design of trimount truck, this one with equalizers whose lower edge was curved upward near the center of the truck. Two brake cylinders were mounted at the outer ends of the truck. Pennsy's U25Cs (as well as their E44s) were delivered with these trucks. The Rivarossi rendition is the only one known.

Fairbanks-Morse single-equalized trimount truck

Fairbanks-Morse designed their own C truck, featuring a light, single-equalized design with a 13 foot wheelbase. It was roller-bearing equipped. It replaced the Commonwealth cast truck, and was found under Pennsy H-24-66 Trainmasters. Athearn's Trainmaster features a somewhat crude cast metal rendition of this truck.

EMD Flexicoil truck

Produced in several versions, the Flexicoil truck featured roller bearings and had a 13 foot 7 inch wheelbase. It was available in the following phases:
Had evenly spaced axles and high mounted brake cylinders. Had two "teeth" on the underside of the base casting between each pairing of axles. Used on SD7 through early SD35 and also on ay 40-Series units that had clasp brakes until mid-1968 (including an entire order of UP SD45s). PRR SD7s, SD9s and SD35s were equipped with these. The Proto 2000 SD7 and SD9 come with a nice rendition. The Athearn SD9 also has one. The Atlas/Roco/Con-Cor SD24 and SD35 have one with axle spacing which instead matches the E8 A-1-A truck.
The same as above, but with low mounted brake cylinders. EMD's last two SD35Xs had this casting.
The same as C1 but with one brake shoe per wheel. Strictly a rebuild used on some Conrail SD50s.
This was a low brake Flexicoil, and was used from late SD35 production to mid SD40/45 production, around mid-1967. All PRR SD40s and SD45s through 6169 were delivered with these trucks. The Kato SD40 (and possibly SD45) has one; Train Station Products makes an aftermarket version for the Bachmann SD45 (and presumably the same version for the Athearn)
Bachmann Spectrum SD45 with Train Station Products sideframes
This had a high outboard cylinder, and the inboard low cylinders are raised above the predecessor C2L. The high cylinder was on the left side, and only one side of the truck had this arrangement, the other had two low mounted cylinders. It was used late 1966/early 1967 to mid-1968 on orders with single-shoe brakes.
This was used starting in mid-1968, and had 2 high mounted cylinders at the outer ends of the truck. PRR SD45s from 6170 through 6234 (the last) were equipped with these. The brake pad setup on one side was a mirror image of the other, instead of being symmetrical. The Bachmann SD45 comes with a version of this truck as shipped. (The Spectrum version is slightly less crude than that on the older, Bachmann Plus, version.)
This version had 3 high mounted brake cylinders and double-clasp brakes. It was used first in mid-1968 on some UP SD45s. The IHC SD35 comes with a model of this truck.
This was a lightweight, export version also used on some Milwaukee SDL39s.

GSC FB-3 truck

This truck, one model of FB-3 made for GE, has a wheelbase of 13 feet, 7 inches. Early versions had two low mounted brake cylinders, while later ones (actually made after the design was sold to Rockwell) had high mounted cylinders at the ends of the truck frames. An intermediate version, made by GSC before the designs were sold to Rockwell, also had high cylinders, but were of a different casting. Five sets were made for Southern U30Cs. Atlas offers the late version, whereas the PRR U28Cs used the early one. This was used interchangeably on GE 6 axle units with the Adirondack version. FB-3 stands for "Floating Bolster, 3 axle". One axle has a single brake shoe; That one is always closest to the short hood.
Atlas U33C(with late "GSC")

Adirondack FB-3 truck

This truck, also made for GE, has a wheelbase of 13 feet, 7 inches. It also was available with low or high brake cylinders. Atlas produces a low cylinder version, which fortuitously is also the type found on Pennsy's U30Cs. Later versions had 3 brake cylinders and clasp brakes, an entirely different base casting which more closely resembles the GSC truck but has the casting holes offset toward the outside axles instead of being centered. Train Station Products makes an Adirondack which is a cross between the early and late Adirondacks, but will not fit on Atlas trucks.

Alco Hi-Adhesion truck

These trucks, with a wheelbase of 13 feet, 7 inches, were designed by Alco to reduce weight transfer, thus reducing wheel-slip problems on high horsepower models. No PRR units were delivered with these, but the Alco C-636s delivered to the PC and ordered by the PRR were so equipped.


original version used on SD60MACS
Version used on SD75s and later (late '95) SD70s
Larger wheelbase to acommedate the 45" wheels used on all SD80MACS, and Phase I SD90MACS different snubbers also.
Version on SD90MAC-H-IIs (don't shoot) I don't have the faintest clue what the difference is, I just heard/read it is different.

EMD HT-C truck



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