At some terminals, you will notice the conductor pulling on a lever in the street. This lifts the cable upward so the grip can grasp it. At other terminals and at other locations on the system , you will see a noticeable dip in the tracks. This lowers the car, and its grip, to the level of the cable underneath, allowing the grip to grasp the cable.
Among other locations, this happens in both directions where the Powell and California cable lines cross. Adhering to the original cable tradition, the California line, which was built first in is entitled to the upper cable. The Powell Street cable cars, by contrast, must drop the cable from the grip before they cross the California Street tracks.
To prevent the possibility of this happening, there is an alarm system and mechanism under Powell Street on either side of the California tracks to physically force the Powell cable from the grip if it is held too long. This can damage both the cable and the grip. Fortunately, because of the skill of the gripmen this almost never happens.
Watch a Powell gripman approaching this corner, particularly headed north from Market Street. The gripman has to crest the hill firmly gripping the cable. Then, with one hand clanging the bell to keep crossing automobiles from getting in his way, he throws the grip lever forward with his other hand just in time, then coasts with a clatter across the California tracks. Another type is known as the stationary depression pulley. This arrangement requires the cable car gripman to release the cable from the grip as it passes over.
Steel plates or bright yellow lettering painted on the street warn the gripman to "Let Go". Letting go of the cable is necessary when two cables intersect at a crossing, the car passes a particular type of turn called a let-go curve, or when the gripman must release one cable and pick up another. If the gripman did not "let go", then substantial damage would be done to the cables and grip itself. To keep this from happening, these points have a bumper bar and bell feature to ensure safety and prevent damage to the system.
If the grip is not "dropped" at the Let Go notice, then the cable will raise the bumper bar, dropping counterweights, and turning the pulley against the cable, which rings an alarm bell to alert the errant gripman to drop the cable. If for some reason the cable is still not dropped, then the bumper bar forces the cable out of the grip, causing damage however to both grip and cable, but preventing more serious and extensive damage to the system.
The powerhouse is then notified of the incident and inspects for damage to the cable. While snapped cables are very rare, the occasion broken strands do occur. In this situation the cable must be fixed immediately, because a broken strand caught in the grip has been the cause of accidents in the past.
At the powerhouse, the cable passes through a strand alarm, which catches protruding strands and sets off an electric gong, notifying the crew, who can then repair the damage. Once the car has cleared the let-go, the gripman must pick up the cable again. After the let-go point, there is a dip in the tracks, which enables the grip to grab the cable without stopping. Another method is to use the cable lift level, at terminals or areas where the track dip is not available.
The car operator lifts up the level and the pulley in the slot raises the cable into the grip. Major cable innovations occurred in the s with such inventions as the steel cable and the detachable grip. During this time period, cable was largely used for industrial purposes. Cable was first adapted for human transit in the form of cable cars, with cities such as San Francisco and Chicago pioneering this mode.
As transit technology shifted to electric power, these systems became largely obsolete. At this point, around the s and 40s, cable, for the movement of people, shifted to the recreational market, where it continued to grow and innovate until the last few decades. If the gripman fails to adjust the grip properly for the grade two things can happen. Too tight and he can't sink the grip fully. Too loose and the car does not grab the cable tightly enough. In either instance, the car starts slipping on the cable.
The gripman must stop and, on the conductors bell signals, back the car down to the bottom of the hill, adjust the grip and try it again. There is considerable wear on the mild steel dies which are the part of the grip that actually close on the cable.
They act a bit like a clutch in a motor vehicle but the dies wear out in about four days. If they wear out while the car is in service, the grip is replaced on the street.
In March Muni started to replace its existing grips with a new design that was bigger, heavier, and safer than the prior model. Each of the new grips contains pounds of steel and five pounds of brass. Almost pounds of that steel is in high-strength castings. The new grips have more parts than the former grips — 62 different types of parts and separate pieces. How the Powell and California lines cross. The Powell cars heading towards Market Street coast across California Street, picking up the cable by means of a dip in the track, or "take rope" as it is sometimes called.
Northbound Powell Street cars coast downhill three blocks before picking up the cable at Jackson Street. The Cal Cable line, which had the prior franchise, had the right to run its cable above the Powell Street company's, avoiding the problems associated with letting go and picking up the cable.
The blueprint below illustrates how the Powell Street and California Street lines cross. The lower cable is the Powell Street, showing that Powell Street grips must be released from the cable before passing over the California Street line.
The stationary depression pulleys force down and hold the Powell cable below both its normal distance below the street and that of the California cable.
Powell cars at the "Let-Go" plate must have their grip disengaged from the cable. The bumper and bell provide a warning to the gripper, if they have failed to "Let-Go. Photo: The cable car intersection of Powell and California is controlled by a signal tower. This is necessary since the grip person on an uphill car cannot see automobiles or cable cars on the other street and may not have time to make an emergency stop at the intersection.
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