Caboose

Overview

A caboose is the crew car that for more than a century rode at the tail of a North American freight train. It carried the conductor and rear brakeman, gave them a place to ride, sleep, eat and keep the train paperwork, and gave the conductor a raised view along the train roofline to watch for trouble. It is a self-contained small building on wheels: a steel Steel Underframe carries the Body Shell shell, the Cupola rises from the roof for the lookout, two Friction-Bearing Truck trucks take the ride, and Knuckle Coupler couplers join it to the train. Inside, the Crew Interior, Heating Stove and Electrical System systems make the car habitable, the Brake System lets the crew brake the train, and the Marker & Signal Lamps tell following trains where the rear of this one is. The caboose has no traction of its own; it is hauled like any freight car, and almost all of its content is built around crew safety and observation rather than cargo.

Underframe and body

The structural spine is the Steel Underframe. A heavy Center Sill runs the length of the car and takes the buffing and draft forces that pass through every car in a train, two Body Bolster bolsters transfer the body weight down onto the trucks, and the Draft Sill & Pocket pockets house the coupler shanks and draft gear at each end. Open End Platform platforms with railings and rows of Grab Iron handholds let crew climb aboard and ride the steps during switching.

On top of the frame sits the Body Shell shell. A Body Framing skeleton of posts and carlines carries two Side Wall Panel panels, two End Wall walls, and the Roof Sheathing sheathing. Six Side Window windows light the interior, two End Door doors open onto the platforms, and a Roof Running Board roof walkway lets a brakeman move along the top to set hand brakes, a routine task in the era before train-line air brakes reached every car.

The cupola and crew lookout

The feature that makes a caboose recognizable is the Cupola, the raised glazed box on the roof. A Cupola Box sits above the main roofline with Cupola Window glazing on all sides, and a pair of elevated Lookout Seat seats let the conductor and brakeman sit high enough to see over the train. From there they watched for a hotbox, the smoke or flame from an overheating Journal Box plain bearing, and for shifted or dragging loads, both of which could derail a train before radios and trackside detectors existed. Bay-window cabooses replaced the roof cupola with a side bay for the same purpose at lower height.

Trucks, wheels and bearings

Each Friction-Bearing Truck is a two-axle truck built from cast-steel Truck Side Frame side frames and a Truck Bolster cross member whose center plate carries the body. Two Wheelset wheelsets, each a Axle pressed with two Steel Wheel steel wheels, run in Journal Box plain journal bearings packed with oil and waste. The ride is sprung by Coil Spring truck springs. Braking at the truck is by Brake Beam beams that press Brake Shoe friction shoes against the wheel treads. These friction journal bearings are what gave the caboose its safety mission: they ran hot when they failed, so someone had to watch the train, which is why the crew rode at the rear at all.

Braking and coupling

The Knuckle Coupler at each end is an automatic knuckle coupler. A cast Coupler Knuckle & Head head interlocks with the mating car, a Draft Gear pack cushions the pull and shove between cars, and a Uncoupling Lever lets a switchman part the cars without going between them. Braking uses the Brake System. The AB Control Valve reads pressure changes in the Brake Pipe & Angle Cocks train line, charges the Air Reservoir, and admits air to the Brake Cylinder, which pushes the rigging to the shoes. A Pressure Sensor gauge lets the crew read pipe pressure, and a Hand Brake with its Hand Brake Wheel and Helical Gear Pair gearing sets the brakes by hand when the car is parked. The air brake is fail-safe: if the brake pipe parts, pressure drops and the brakes apply on their own.

Crew quarters, heat and light

The Crew Interior is a compact home. A Conductor Desk holds the waybills and train log, Crew Bunk bunks fold down for rest on long runs, Storage Locker lockers stow gear, and a Galley Counter counter with a Water Tank and a Hopper Toilet covers meals and sanitation. Heat comes from the Heating Stove, a cast-iron Cast-Iron Stove Body burning coal or oil, vented through the Stove Flue & Roof Jack roof jack, fed from the Fuel Bin and guarded by a Heat Shield. Power comes from the Electrical System system: a Axle Generator driven off an axle by a Drive Belt charges the 12 V Battery, which feeds Light Fixture lamps through the Electrical Control Panel. Finally, the Marker & Signal Lamps hang Rear Marker Lamp red lamps and Class Lamp class lamps on Lamp Bracket brackets, marking the rear of the train. Modern end-of-train telemetry devices later took over that last job, which together with reliable roller bearings and trackside hotbox detectors is why the caboose largely disappeared from regular service.