I'm getting ready to replace the front pads on my 83 240D and was wondering about the sensors. How do they work? I worked on one car and the sensors had a wire that was cut when the sensor touched the rotor, requiring replacement. (Toyota i think) My light is coming on when I apply the
Brakes. will I have to replace the sensors also?
Jon J

83 240D 147K
81 240D 325K

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Jon J.
81 240D

Not necessarily.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

They are cheap enough. I would do it anyway.

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USUALLY. the wires are near impossible to remove without breaking them. it can be done, but they are not expensive. also, they get worn when they contact the rotor, so they are likely needing replacement anyway.

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$1.25 for the sensor. 1983 Mercedes Benz 240d BrakeProduct Subcategories - Peachparts

I'd use the link (or order the sensors) to get an idea of how the connect and where to pull them from.

Read up on cleaning the caliper and lubing the sides of the pads.

That must be the $1.25 versions!!! I still have the original sensors in my '82 300D. They have been in and out a number of times in the past 29 years.

The sensors work by a wire contacting the rotor after a certain amount of wear, tripping the idiot light. By this time the sensor is damaged. Therefore,

If the light has come on when you replace the pads, you will need to replace the sensor.

If the light has not come on when you replace the pads, you will not have to replace the sensor.

Jon J

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Jon J.
81 240D

I have reused my sensors for years and they work fine. Just be careful pulling them out of the brake pad hole. 81 300SD.

Mine were worn through the wires. I was quoted a price of $65 each by the idiot at the authorized stealer. Because of the "price " I thought it was a much more expensive proximity switch . that was the reason for the how does it work question. (unanswered) I have a very limited amount of time to work on my car and its 85 miles to a good parts house. So the more I know the better. Oh well they are cheep and easy to replace. (now I know)
Jon J

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Jon J.
81 240D

It's real simple. When the pads wear through to the "sensor," the end of the wire makes contact with the rotor, completing the ground circuit for the warning light.

Like a lot of things, it's a matter of degree. It depends on how long you keep driving after seeing the light for the first time.

It was clearly stated in one of the above posts. If you are replacing the pads before the sensor turned on the light it is highly likely that they are easily reusable. If the light has come on, then it has worn through the insulation on the sensor and it would be best to replace it. I've had good luck reusing ones that had not worn through.

Use a thin coat of dielectric grease on the post when securing the connector.

Hope this helps.

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[QUOTE=LarryBible;2841914]It was clearly stated in one of the above posts. If you are replacing the pads before the sensor turned on the light it is highly likely that they are easily reusable. If the light has come on, then it has worn through the insulation on the sensor and it would be best to replace it.


That was my post I made AFTER i did the brakes. Yep that's me alright I recognize the name. You're right it is clear,,,,, now.
Jon J

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Jon J.
81 240D