Cable Car

Overview

A Cable Car is a street railway vehicle that carries no engine of its own. It is pulled along by a steel wire rope, the cable, that runs continuously in a conduit beneath the street and is driven from a central powerhouse. The car connects to that cable through a Grip Mechanism, a clamp the operator opens and closes by hand. The first line of this kind opened in San Francisco in 1873, and the surviving system there still works the same way. Because the cable moves at a fixed speed, the car has no throttle and no transmission. The operator, called the gripman, has only two decisions to make: grip the cable to go, or let go and brake to stop.

The Carbody is wooden, roughly 27 ft long, built on a steel-channel Body Sill Frame. It is split into an open front bay with outward-facing benches and an enclosed rear cabin. Two single-axle Truck Assembly units carry it on 3 ft 6 in gauge track. Those wheels only roll. They drive nothing, since every bit of tractive effort comes from the cable.

The Grip Mechanism

The grip is the part that makes a cable car a cable car. The gripman pulls the Grip Lever on the platform, and through a Grip Toggle Link and a Grip Cam Block that lever closes two Grip Jaw members onto the moving cable. The cable itself is never touched by bare steel that matters: the wearing surfaces are replaceable Grip Die inserts bolted into the jaw faces. A partial pull lets the dies slip on the cable so the car accelerates gently up to cable speed; a full pull clamps hard and the car is locked to the rope at the full 9.5 mph. A Grip Quadrant with a pawl holds the lever at the chosen position, and a heavy Grip Return Spring springs the jaws open the instant the gripman eases off. The dies take a brutal beating and are swapped out every few days; a Grip Take-up Screw takes up the wear between changes. Small Cable Guide Pulley sheaves steer the cable cleanly into and out of the jaws.

Grip Running Gear

Getting the grip down to the cable is its own problem. The cable rides in a conduit under the road, reached only through a narrow slot about 0.75 in wide between the rails. The Grip Shank is the vertical bar that drops through that slot, with a thin Slot Blade riding in the gap, the one part of the whole machine visible at street level. The shank hangs from a sliding Grip Carrier Frame under the body, kept centered by Grip Guide Roller rollers. Where two cable lines cross, one car must let its cable dip out of the way, and a Depression Bar pushes the rope down so the crossing line runs clear.

Braking

With no motor to brake against, a cable car carries four independent braking systems in its Brake System. The fastest input is the Cable Release Linkage: open the grip and the cable runs free, so the car simply coasts. For service stops the gripman uses the Track Brake, pressing long Pine Track Brake Shoe blocks of Monterey pine straight down onto the rail heads with the Track Brake Pedal. Under hard braking the pine actually scorches and partly fuses to the rail, so the shoes wear out in days and are treated as consumables. The conductor can add the Wheel Brake, cast-iron shoes drawn against the wheel treads by a Brake Hand Wheel and chain. The last resort is the Slot Brake: a steel Slot Brake Wedge driven down into the street slot, which jams the car so hard it sometimes has to be cut free afterward. All of it links back through the Brake Rigging of rods and levers.

Body and Trucks

The body framing is hardwood, with Oak Body Post posts on steel Steel Channel Sill sills, sheathed in tongue-and-groove Body Side Panel boards and topped by a raised Clerestory Roof for light and ventilation. Each end rides on a Truck Assembly built around a Truck Frame and a Wheelset of two Flanged Steel Wheel wheels pressed on an Axle Bar. Plain-bearing Axle Journal Box housings, each with a bronze Journal Bearing and an Oil Seal, support the axles, and Coil Spring truck springs cushion the Truck Bolster that carries the body Center Pin.

How the Gripman Works It

The crew stand at the Platform & Controls amidships. There is no controller and no throttle, only the Grip Lever, the Track Brake Pedal and the Slot Brake Lever for emergencies. Starting means slipping the grip onto the cable smoothly so passengers are not jolted; on a downgrade the gripman drops the cable entirely and rides the track brake to hold 9.5 mph. Approaching a stop, the gripman releases the cable and applies the pine shoes. The conductor signals with a Conductor Bell Cord, works the Wheel Brake, and collects fares at the Fare Box. A foot-rung Roof Gong, worked from the Foot Gong Treadle, warns traffic at every crossing.

Interior, Fittings and Variants

The Interior mixes outward-facing Open Bench seats with Reversible Seat Back backrests in the open bay and longitudinal Cabin Bench seating in the closed cabin, with Grab Strap straps for standees. Single-end cars must be turned on a turntable at each terminus because the grip and platform face one way; double-end designs avoid that. End fittings include Headlamp lamps, Route Sign boards, a brass Builder’s Plate and a slatted Wheel Guard (Pilot) wheel guard at each end to sweep the track clear. The whole vehicle is a study in doing one thing well: gripping a moving rope, and stopping safely once you let go of it.