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Brake pad wear sensors - Do we need them?

3.7K views 17 replies 5 participants last post by  GearheadGreg  
#1 · (Edited)
Have you ever driven your 107 or other classic car enough for the brake light to come on?

I am just putting finishing touches to my W123 brake job and found that I couldn't find the spare sensors I thought I had :)

Led me to wonder why I needed them at all! New brakes will likely see under 40k miles in next 10 years. By that time (or earlier) they may take my license away! Or one of us may expire (me or car?)

I put one on each side as a compromise ;) None available locally.
 
#4 ·
Sounds like you will perform what the sensor is supposed to do...? When the pad wears down far enough, it grinds the senors away, breaking continuity of an electrical signal, then the dashboard lights up. If you cut wires, MB will tell you time to replace your pads by lighting up the idiot lamp.
When I replaced my pads, lucky me- the wires were not broken. I folded them, zip tied, and did not remove anything at all. Many 1000 miles later, they're doing fine.
 
#5 ·
Sounds like you will perform what the sensor is supposed to do...? When the pad wears down far enough, it grinds the senors away, breaking continuity of an electrical signal, then the dashboard lights up. If you cut wires, MB will tell you time to replace your pads by lighting up the idiot lamp.
When I replaced my pads, lucky me- the wires were not broken. I folded them, zip tied, and did not remove anything at all. Many 1000 miles later, they're doing fine.
I think you have that backwards. The sensors cause the brake light to go on when the pads wear through and the sensors get grounded against the rotors.
 
#6 ·
I'd like to learn what happens. As I was told, there's actually two wires inside and it's the wire-duet's job to get severed, breaking continuity, not a single wire getting it's insulation rubbed off and grounding the circuit. I was told don't cut em unless I can live with the dash light, (or in his case, remove the light too because racecar). When do you plan to do the maneuver? You said you have spares so the procedure is reversible.
 
#7 · (Edited)
I'd like to learn what happens. As I was told, there's actually two wires inside and it's the wire-duet's job to get severed, breaking continuity, not a single wire getting it's insulation rubbed off and grounding the circuit. I was told don't cut em unless I can live with the dash light, (or in his case, remove the light too because racecar). When do you plan to do the maneuver? You said you have spares so the procedure is reversible.
I already have - No brake light. There is just one wire - this is on an '85 W123. Different car, but same era. According to vendor sites, sensor is the same on 380SL and even on my 72 107.
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I have no spare sensors and none are available locally, so going with one each side and the other socket protected with a cut off bad sensor. Other than filling the connector sockets, I see no need for the sensors on this old car! Or on my 107, for that matter :)
 
#10 ·
When I switched calipers on my 1999 E320, I was missing one wear sensor. Like you, it was unlikely I would ever see the wear sensor activate in the future. I also check my brakes for wear every time I rotate my tires (~6 to 7K miles).

I did eventually replaced it though as it bother me knowing it was missing and the part was less than $5.
 
#11 · (Edited)
I will likely buy sensors some time when ordering on-line. Some places want crazy prices for them $10 at NAPA here for one type. Others on-line have them for $0.77!

I seem to recall that our E320 has three sensors - one on each side in front and one on one side at back. Some cars apparently had one in front and one in back. But my W123 (and likely 107) has 4 sensors in front - none in back.

Another snippet - Apparently the sensors can cause AM radio interference. Mercedes bulletin says to cut them off! And then says "As of Model Year 2006 (806), the 50% brake wear sensor has been eliminated from series production vehicles."

I guess that answers my question :)
 

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#14 ·
I finally got the wheel off of mine & took a picture. I do have two wires going to my caliper. I do confess my information came from a Porsche guy, that when I sent home an image and asked, he elaborated 'one wire or two going to the caliper, not the sensor wires themselves?' He said both systems came on Porsches:the single was a wire you can cut, as it grounds-out through the rotor, and the 2-wire was a series-circuit & do NOT cut that one.. the ziptie trick is what he does for racetrack as they swap pads every weekend.
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#15 · (Edited)
I finally got the wheel off of mine & took a picture. I do have two wires going to my caliper.
I have those same two wires on my 107&123. One goes to one pad and the other to the other one. They are single wire sensors that are designed to ground out when pads are worn. I can understand the misunderstanding :)
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#18 ·
My Porsche friend that gave me the info races with mid 80's 944's. He was certain that we had the same calipers and same everything (brakes), actually. His racing class is strict with OEM,which is why he has to keep the sensors intact, otherwise he said he would omit the whole system. I'm confident he's not using your '05 sensors. It sure looks like your sensor would be a series circuit though.