5.7. COUPLER MAINTENANCE
Regulations cover all phases of maintenance requirements on couplers; however, most of them are minor
in relation to the two important requirements discussed in the following subparagraphs. These two requirements
deal with the proper coupler height from the rails and the amount of play in the knuckle.
a. Coupler height. If the coupler is too low, cars do not couple properly; then, when they are moving, it is
possible for them to uncouple. Coupler height is measured from the top of the rails to the center of the face of
the coupler knuckle using the tool shown in figure 5.6. Because of the difference in weight pushing downward
on the car, different measurement requirements exist for empty and loaded freight cars. On empty cars, the
knuckle centerline must be raised to 34 1/2 inches if it is 32 1/2 inches or less from the top of the rails. A
coupler on a loaded car must be adjusted to 33 1/2 inches when the knuckle centerline drops to 31 1/2 inches or
less. The height of a coupler can be adjusted by adding shims beneath the truck springs, or between the center
plates on the truck and the body bolsters, or both.
b. Coupler knuckle play. Excessive knuckle play causes the distance from the knuckle to the guard arm to
be too great when the coupler is in a locked or closed position. When this occurs, the coupler parts from its
mate. In chapter 2, the full name of the wheel-defect gage was given; part of its name is worn coupler limit.
Figure 5.7 shows this gage being used to measure coupler knuckle play. If the opening between the knuckle and
the guard arm is too large, one of three things may be causing the defect: the guard arm may be out of contour
and the entire coupler may need to be replaced; the knuckle pin or the knuckle pin hole may be worn and either
one or both of the parts should be replaced; or the knuckle face or the lock fulcrum may be worn and the
knuckle should be replaced or the lock fulcrum built up by welding. If two or more of these causes exist at the
same time, it would probably be safer and cheaper to replace the entire coupler.
5.8. FOREIGN COUPLERS
Although most of the rolling stock in North America is equipped with automatic couplers and draft gear
that absorbs both pulling stress and impact shock, most foreign countries do not have railway cars so equipped.
The hook-and-link and Willison couplers are found in most oversea areas except in Korea, Japan, and China
where AAR automatic couplers are used. Because military railway