The above diagram shows the pedal as if you were looking at it as it sits in the car from the driver's side. It's as if you're looking at the side of the car from the driver's side door with the side of the car cut away. The numbers below don't correlate to diagram above--they are order of operations:
- The pedal and switch are pressed by the driver they move towards the firewall.
- The "slack" or "play" that exists where the pedal stub (diagram part #2), and the push rod meet (diagram part #1) is shifted (yellow shaded area)
- The push rod moves a few millimeters into the switch.
- The spring is depressed
- The plunger inside the spring is now pushing against the (hot) metal blade which makes contact with the brake light side of the switch (diagram part #5)
- The circuit is now closed and power travels to the brake lights
The Problem
The flat side of the master cylinder push-rod (part #1) was not quite thick enough to make enough contact with the switch to push the hot side of the switch into the brake light side of the switch. There could have been different ways to remedy this issue.
- Drill out the hole in the push rod to create more slack or play so that it traveled further when the pedal was pressed.
- Add some weld to the flat part of the push rod so that when it started moving into the switch it could make enough contact to trigger the brake lights.
- Add a shim between the push rod and the switch so that the push rod could make enough contact to trigger the brake lights (similar to #2)
The Solution
For me it seemed easiest to try solution #3 (adding a shim between the push rod and switch). I also had to cut off about 1 coil from the spring, but I had tried that first anyways before getting to the shim solution. If I had used a thinner shim I probably wouldn't have needed to cut off a coil from the spring.
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| Shim Front View |
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| Shim Side View |
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| Shim Installed on Switch |
The shim was crafted out of an aluminum "L" bracket that I had sitting on a shelf in my garage. I just used a hacksaw to cut it to the length and width that I needed. I left enough length to bend both ends to wrap around the switch to ensure it didn't fall off. If I had a thinner metal or even a grinder to make the metal thinner I could have gotten by without needing to shorten the spring. I installed the switch back on the brake pedal/push rod although I don't have the plastic washers that go on either side of the switch.
Now the circuit is closed as I lightly press the brake pedal. This is important since it takes very little pedal travel for the car to stop now that I've got the power booster installed.
I took the liberty to buy the "DISC BRAKE" rubber pedal to replace my standard brake pedal since I expected to spend money on a new brake light switch anyways.
