Anatomization of Brakeswitch .. after a shift lock error!


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It happened out of sudden, out of nowhere. I was referring to the incident where my shift gear was stucked at Park position, as I was trying to drive off to pick up my parents in-law. Darn, I was mumbling to myself, “I hope this is not a sympton of aging car”, as my dear bora is reaching its 3rd year birthday in a month time.

As a car-idiot, and having hear alot of horror stories about auto transmission problems and overhaul, I was quite nervous, given that the first sympton of the problem (stuck shifter) had some relation to transmission. Is this a beginning to the mirror history of my old peugeot, where mechanical & electrical issues cropped up one after another every month, as if they were well planned for. And … my last car problem related incident was flat battery a month ago.

With alittle panicky, I rang Autospritze’s Dennis and Heng. It was Sunday morning, and I guessed it was a little early for them, after a long 6 days of hectic work. I rang up Raymond subsequently, and while he was also unsure about the cause of the problem, he accurately suggested non-stop stepping of the brake pedal to get the shift gear out of the Park position. While doing so for few minutes, Autospritze’s Heng responded to my earlier SOS call. He was in Malaysia, he too suggested the same thing, and true enough, after some preservance and patience, I felt the shift gear was finally unlocked momentarily when the brake pedal was stepped. Not wanting to miss this “momentary” opportunity, I quickly shift the gear to Drive position, as fast as I can, just like how the cowboys would draw their gun in split seconds in those cowboy show!

Not wanting to get myself in the stucked position again, I pulled up my e-brake whenever I want to stop my car while the gear is in D mode. At this moment, Autospritze’s Dennis had also just waken up from his beauty sleep, and he suggested that I bring the car to his workshop for repair the next day, and from the sympton of the problem and workaround, we all suspected that the brake switch is faulty.

The function of brake switch is two fold. When a brake pedal is depressed, it triggers two thing via the brake switch, which sense the depression and power the brake light. It also triggers a shift gear unlock signal, so that the shift gear can be unlocked from its current position. It’s a safety feature in all automatic-transmission based vehicles, whereby the gear must not be able to shift freely from “N” and “P” position to other mode.

True enough, a replacement of a new brake switch solved the problem.
A further check with VWvortex via its search engine, using “brake switch” as the search key words, return numerous threads that articulate the same problem as I had gone through, as well as the desire fix. A big thumb up for VWvortex, for its great knowledgebase, although I did not benefit from it directly in this particular incident problem (Now I would really appreciate accessing Vwvortex using my GPRS in the future!)

One particular thread in VWVortex actually threw in some insights with regards to the detail technical cause of the problem. Intrigued by the insights, I decided to do a full anatomization of the faulty brake switch, for the sake of knowledge gain, and of course the itch to tear out the parts!

The steps to anatomize the brake switch

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1. This step is optional, but it makes the subsequent steps alittle more easier. First of all, remove the pin cover, by prying the pin cover groove alittle (as shown by the red arrow) so that the the pin cover can be slotted out in the direction indicated by the green arrow.

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2. Push in the pin stopper as shown by the red arrow, and push it out in the direction by the green arrow. When the pin is pushed out alittle, use a pen knife or equivalent to push the edge of the pin as shown in the diagram on the right.

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3. Pull out the pin as shown in the diagram. The fault lies on the pin itself, so subsequently steps are not necessary, but it facilitate a better understanding of the what, why and how of the problem and resolutions.

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4. You will notice there’s two tiny stopper, one on each side of the cylinderical-shape part. One of them is at where the pen-knife is pushing, in the diagram on the left. When the stoppers are pushed in slightly, pry and push up the round cover as shown in the diagram below.

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5. When the cover is taken out, a spring will sprung out, remove the spring

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6. Push the thin rod at the other end of the cylindrical block, and that pushes out the plunger as shown in the diagram below

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At this point of time, all the sub parts of the brake switch are dis-assembled, and it’s time to diagnose the mechanical/electrical function of the brake switch, and its point of failure.

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Item 6, I called it plunger, and the plunger rod actually stays in contact with the brake pedal mechanism. When the brake pedal is depressed, it will push the thin rod.

Item 2, with the spring, it creates some tension as the brake rod is being pushed by the brake pedal mechanism. Once the brake pedal is released, it also release the tension of the spring, which will then pushes the “brake connector rod” (item 6) back to its original position.

Item 1, 5 and 4 are just covers, serve no working functionality.

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Item 3, is the brake switch pin that connect and complete a circuit for the brake light and shift lock. Upon further inspection of the pin, I noticed that the back of 4 pins are aligned perpendicular to with the 2 horizontal metal strips. There is 1 tiny stopper on the otherside of each of these 2 metal strips. The 1st 2 pins are in contact each of the 2 metal strips respectively, creating a close circuit. When there’s something that pushes either of the tiny stoppers, it will result in open circuit for the affected pin.

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One of the circuit indicates turning on of brake light and shift lock, while the other indicates a turn-off.

The diagram above simulates how the item 6 (brake connector rod) stays in contact with the tiny stoppers on the pin via a notch at the bottom of connector rod.

Now, there are two possible point of failure.

PoF #1 One is where the two pins are not staying in contact with the corresponding metal strip, when the tiny stopper is not pressed down. You can inspect this possible point of failure when you take out the pin. In my case, the construction of the pin is still in working condition, so this is unlikely the point of failure.

PoF #2 The other is where most of the Vwvortexers commonly faced. The contact point between the pin and the metal strip is bad due to oxidisation of the metal. In my case, I notice that the metal strips are badly oxidised already, hence, even if contact is made, there might not create a close circuit.

Solution ? either you clean the oxidised contact surface with alcohol, or you invest US$15 for a new brake switch.

Other references

1. Brake switch removal (from car)
2. JE’s Brake switch repair

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