TM 55-203
Figure 3-1. AAR standard 4-wheel, coil spring, cast bolster car truck.
b. Axles. A car axle is a solid axle with either solid
3-5. Underframe
The underframe is the framework which receives the
holds the wheels to gage, it also transmits the load from
buffing and pulling stresses and carries the combined
the Journal bearing to the wheels. The extreme ends of
weight of the car and lading. The underframe consists of
the axle are known as journals; these are turned to size
all the framing below the floor, including the sills (center
and then burnished to a polish. That portion between the
and side), platforms, bolsters, crossbearers, crossties, end
wheel seat and the back journal fillet seats the dust guard
sills, striking plates, and required safety attachments.
and is therefore known as the dustguard collar. The
(See chapter 5 for discussion of underframe assemblies,
wheel seat follows the dustguard collar.
The axle
etc.)
diameter at this point is fixed by regulations covering
standard axle dimensions and condemning limits
3-6. Draft Gear
(minimum diameters and maximum lengths for which an
The draft gears located at each end of the car connect the
axle will be continued in. service). Wheels and axles are
coupler to the underframe. The ends of the draft gear
fully discussed in paragraph 4-3 through 4-11.
bear against the shoulders of the draft casting or lugs,
which are riveted or
3-2
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