I have been wondering how the parking brake lever works.
People have had it fail, and it was not clear to me what failed.
This is how it works:
1. Here is an overview of the passenger side of the parking brake lever assembly.
The pin which loops over the black lever is installed to keep the tension spring from unwinding. It is removed after the cables are connected.
2. Here is an overview of the driver's side of the parking brake lever assembly.
3. A more detailed view of the various parts.
The tension spring is attached to the cable drum.
It keeps about 20 pounds pull on the cable when the parking brake is released. This removes the slack from the system.
The cable drum is made from two pieces, with one piece extending under the clutch spring.
The clutch spring is wound around the drum tightly enough to be a friction fit on the drum.
One end of the clutch spring extends from the bottom of the spring, and is anchored to the parking brake lever.
Lifting the lever causes the clutch spring to wind even more tightly around the drum, so the drum rotates with the lever, which pulls on the brake cable.
4. As the lever is pulled up, the clutch spring, being anchored to the lever, rotates, tightening itself on the drum.
This drags the drum around with it, pulling the cable.
The clutch spring tail moves away from the stop, which is actually the thing that allows the clutch spring to wind itself tighter on the drum.
5. Here the lever has been raised as if to apply the parking brake.
The spring clutch tail has also rotated away from the stop.
If you were to pull on the tail, toward the camera, it would unwind the clutch spring, making its diameter bigger, thereby releasing the cable drum. The lever position would not change, though. It would move freely as long as you followed the rotation with the spring tail.
When the lever is returned to the down position, the clutch spring tail also rotates toward the stop. It hits the stop just before the lever bottoms out. This releases the clutch spring, and the tension spring is free to rotate the cable drum, maintaining 20 pounds tension on the cable.
6. Here you see what breaks when you go to apply the parking brake, and hear a loud SNAP!
The lever will then be free to move, and no torque will be applied to the cable drum.
An ineffective parking brake could be caused by any one of several things:
Shoes out of adjustment
Broken clutch spring arm
Slipping clutch spring
Broken tension spring