Is there a reason that most electric MU cars don’t use knuckle couplers? The Long Island Railroad EMUs use a coupler that has a knotched pin, with a receptical next to it.Tjis requires the railroad to have locomotives with these couplers postioned outside the East River Tunnels to rescue stranded MUs.
Most transit operations use an automatic coupler that includes all it’s air and electrical fittings in the coupler housing. It elminates needing to go inbetween to cut in and out air hoses and other fittings, amongst other benefits.
The N2a coupler also has zero free play. so nearly no slack in couplers other than play in drawgear.
To add to dutchrailnut’s comments, I am most familiar with the old MU electrics on the IC’s Chicago suburban operation. These cars were not connected by cables but rather relied on mere contact of electrical control connections between adjacent cars. This was made possible only by having zero slack couplings which could not be achieved with knuckles. Trains were made up of two car sets, a power car and a trailer. Thus trains of 2, 4, 6 and 8 cars could be hastily made up and broken down without having to connect and disconnect control cabling. There was no draw bar slack and none was required since each set of two cars had its own motor power. I presume that MU cars of other railroads and subways relied on the same system.
Mark
From what I understand knuckles are also a little more picky about how they’re set up after coupling/uncoupling - is the pin up or down? Many of the reduced slack or slackless couplers were spring loaded, which meant that they were always ready to couple/uncouple and you didn’t have to worry about weather the pin fell or not. Just wait till you heard the thunk and go.
Also, knuckles are designed to have a degree of vertical play built into them - if one knuckle is a few inches higher than the other knuckle, it will still couple, the higher knuckle will just not be touching the lower knuckle for a few inches. This means that freight cars with variations in knuckle height can couple without hassle or problems, avoiding having to maintain very strict height tolerances. The knuckles can slide a little bit up and down while coupled (in theory, I think you could lift a car right out of a train, straight up, assuming no air connections.) If there are electrical control lines that need to meet up evenly, a knucle will not do this, because there’s nothing on it to evenly match the height of the coupler on both cars. Many of the transit style couplers guide the actual connection into place, allowing for a tight connection of electrical control lines. This means that transit coupler heights may need to be kept within tighter clearances, but it makes making and breaking trains a lot easier, and shouldn’t be as hard with couplers that don’t have as much slack tossing them around under the end of the car.