Member Since: 03 Nov 2013
Location: SE England
Posts: 45
How does the brake wear sensor actually work?
Ok, so it clips into the inner pad, I know that much.... but how is it actually working? As in how is it making an electrical short circuit when the pads aren't worn and then open circuit when they are worn? Does the plastic body of the sensor get pushed out leaving the brass contact behind on the pad until it breaks contact with terminals in the sensor head? That's the only conclusion I can come to
If so, how does the pad moving sideways, as it wears, push the sensor body outwards? Is there a ramp on the carrier that it rides up? Would be nice to know though... I should have looked closer when I changed the pads
Thanks
9th Jun 2016 1:21 pm
Disco_Mikey
Member Since: 29 May 2007
Location: Dundee, Scotland
Posts: 20844
Wear sensor is closed circuit. When the pad wear, it breaks the circuit (open circuit) which brings the light on My D3 Build Thread
Member Since: 03 Nov 2013
Location: SE England
Posts: 45
I agree whole-heartedly, but how does it 'actually' break the circuit is my question
9th Jun 2016 1:50 pm
Sydney
Member Since: 11 Aug 2013
Location: St Neots
Posts: 903
It wears out on the disk.De-Tango
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9th Jun 2016 1:57 pm
Martin Site Admin and Owner
Member Since: 06 Nov 2004
Location: Hook Norton
Posts: 18563
There's a "pip" (blob) on the surface of the wear sensor, this points at the disc.
The pip contains the sensor's wire link very close to the surface.
As the pad wears, the pip gets closer and closer to the disc, until it touches. It then wears away, and the internal wire is broken.06 D3 SE / 15 LR D90 XS SW / 88 LR 90 Td5 / 68 BMW 2000 ti
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9th Jun 2016 1:57 pm
V8burble
Member Since: 03 Nov 2013
Location: SE England
Posts: 45
Oh ok, so if you wait until the wear sensor light/warning comes up then your sensor can not be reused as it's been worn through on the pip side.... that's a bit rubbish, I preferred my thought
9th Jun 2016 2:08 pm
Martin Site Admin and Owner
Member Since: 06 Nov 2004
Location: Hook Norton
Posts: 18563
If you keep an eye on your brakes and change them before the sensor pip is worn off, then the sensor can be reused.
Just don't lose the metal clip as they tend to ping off and disappear. It's worth keeping the clip from any old sensors.06 D3 SE / 15 LR D90 XS SW / 88 LR 90 Td5 / 68 BMW 2000 ti
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9th Jun 2016 2:11 pm
Brian_DL13
Member Since: 25 Aug 2013
Location: Teesdale
Posts: 1418
Also be aware that (as I found out to my cost) there is only 1 (maybe 2?) wheels fitted with the sensors. Apparently they assume that all the pads will wear at the same rate
9th Jun 2016 3:05 pm
DrRobH
Member Since: 10 Oct 2015
Location: Hampshire
Posts: 927
I have a brand new Genuine front wear sensor for a 2012 Sport going spare. I would imagine it's the exact same part....Visitor from fullfatrr.com
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9th Jun 2016 7:29 pm
V8burble
Member Since: 03 Nov 2013
Location: SE England
Posts: 45
Thanks for all the replies everyone, most illuminating and as usual I've learnt something new again today.
I shall be doing the rear pads and discs in a couple of week's time, that should be interesting, I shall have to follow the brake bible for the EPB business for sure
9th Jun 2016 9:39 pm
V8burble
Member Since: 03 Nov 2013
Location: SE England
Posts: 45
DrRobH wrote:
I have a brand new Genuine front wear sensor for a 2012 Sport going spare. I would imagine it's the exact same part....
Thanks, but my sensor is just fine, appreciated though
9th Jun 2016 9:41 pm
Apache
Member Since: 16 Oct 2011
Location: Yorkshire
Posts: 692
It probably won't be after you remove it to change brakes. They become brittle and frequently self destruct on removal. The more care you take the more likely they are to break (in my experience).
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9th Jun 2016 10:05 pm
Sheepy
Member Since: 20 Feb 2013
Location: Bedfordshire
Posts: 630
Yep, I'm with Beanie - replace them with a wire to short the sensor and fool the car into thinking the sensor is ok and then do visual checks more regularly.
My rear pad with the sensor wasn't worn enough to alert me although it's partner pad in the caliper was almost at the backing plate!
I now check all four calipers regularly, much better approach in my opinion.
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